Los semáforos , semáforos , semáforos o robots [1] son dispositivos de señalización colocados en intersecciones de carreteras , cruces de peatones y otros lugares para controlar los flujos de tráfico. [2]
El primer semáforo del mundo fue una señal encendida de gas operada manualmente instalada en Londres en diciembre de 1868. Explotó menos de un mes después de su implementación, hiriendo a su operador policía. [3] Earnest Sirrine de Chicago patentó el primer sistema de control de tráfico automatizado en 1910. Utilizaba las palabras "STOP" y "CONTINUAR", aunque ninguna de las dos estaba iluminada. [4]
Los semáforos siguen un código de color universal que alterna el derecho de paso otorgado a los usuarios con una secuencia de luces o LED de iluminación de tres colores estándar:
- Luz verde
Permite que el tráfico avance en la dirección indicada, si es seguro hacerlo y hay espacio al otro lado de la intersección. [5] [6] [7] - Rojo luz
prohíbe cualquier tráfico de proceder. Una indicación roja intermitente requiere que el tráfico se detenga y luego proceda cuando sea seguro (equivalente a una señal de alto ). - Luz ámbar (también conocida como 'luz naranja ' o 'luz amarilla ')
Advierte que la señal está a punto de cambiar a roja, y algunas jurisdicciones requieren que los conductores se detengan si es seguro hacerlo, y otras permiten que los conductores pasen por el intersección si es seguro hacerlo. En algunos países europeos (como el Reino Unido ), el rojo y el ámbar se muestran juntos, lo que indica que la señal está a punto de cambiar a verde. [8]
Una indicación ámbar intermitente es una señal de advertencia. En el Reino Unido e Irlanda , una luz ámbar intermitente se usa solo en los cruces de pelícanos , en lugar de la señal combinada rojo-ámbar, e indica que los conductores pueden rebasar si no hay peatones en el cruce.
En algunos países, las señales de tráfico entrarán en modo intermitente si el monitor de conflictos detecta un problema, como una falla que intenta mostrar luces verdes al tráfico en conflicto. La señal puede mostrarse en ámbar intermitente en la carretera principal y en rojo intermitente en la carretera lateral, o en rojo intermitente en todas las direcciones. La operación intermitente también se puede utilizar durante las horas del día en las que el tráfico es ligero, como por la noche. [9]
Historia
Antes de los semáforos, la policía de tránsito controlaba el flujo del tráfico. Un ejemplo bien documentado es el del Puente de Londres en 1722. [10] Se asignó a tres hombres la tarea de dirigir el tráfico que entraba y salía de Londres o Southwark . Cada oficial ayudaría a dirigir el tráfico que salía de Southwark hacia Londres y se aseguraba de que todo el tráfico permaneciera en el extremo oeste del puente. Un segundo oficial dirigiría el tráfico en el extremo este del puente para controlar el flujo de personas que salían de Londres y se dirigían a Southwark.
El 9 de diciembre de 1868, [11] se instalaron los primeros semáforos no eléctricos con luz de gas fuera de las Casas del Parlamento en Londres para controlar el tráfico en Bridge Street, Great George Street y Parliament Street. [12] Fueron propuestos por el ingeniero ferroviario JP Knight de Nottingham, quien había adaptado esta idea de su diseño de sistemas de señalización ferroviaria [13] y construidos por los ingenieros de señales ferroviarias de Saxby & Farmer. La razón principal del semáforo fue que hubo un desbordamiento de tráfico tirado por caballos sobre el puente de Westminster que obligó a miles de peatones a caminar junto a las Casas del Parlamento. [14] El diseño combinaba tres brazos de semáforo con lámparas de gas rojas y verdes para uso nocturno, en un pilar, operado por un agente de policía . La linterna de gas fue girada manualmente por un oficial de la policía de tránsito con una palanca en su base para que la luz adecuada se enfrentara al tráfico. [15] La señal tenía 6,7 m (22 pies) de altura. La luz se llamaba semáforo y tenía brazos que se extendían horizontalmente y ordenaban a los conductores "Parar" y luego los brazos bajaban a un ángulo de 45 grados para decirles a los conductores que procedieran con "Precaución". Por la noche, una luz roja indicaría "Alto" y una luz verde significaría "Precaución". [10]
Aunque se dijo que tenía éxito en el control del tráfico, su vida operativa fue breve. Explotó el 2 de enero de 1869 como consecuencia de una fuga en una de las líneas de gas debajo del pavimento [16] e hirió al policía que lo operaba. [17]
siglo 20
En las dos primeras décadas del siglo XX, los semáforos de semáforo como el de Londres estaban en uso en todo Estados Unidos y cada estado tenía su propio diseño del dispositivo. Un ejemplo fue de Toledo, Ohio, en 1908. Las palabras "Stop" y "Go" estaban en blanco sobre un fondo verde y las luces tenían lentes rojas y verdes iluminadas por lámparas de queroseno para viajeros nocturnos y los brazos eran de 8 pies (2,4 m ) sobre el suelo. [18] Fue controlado por un oficial de tráfico que haría sonar un silbato antes de cambiar los comandos en esta señal para ayudar a alertar a los viajeros del cambio. El diseño también se utilizó en Filadelfia y Detroit. [19] El ejemplo de Ohio fue la primera vez que Estados Unidos intentó utilizar una forma más visible de control de tráfico que implicaba el uso de semáforos. El dispositivo que se utilizó en Ohio se diseñó basándose en el uso de señales de ferrocarril. [20]
En 1912, se colocó un dispositivo de control de tráfico en lo alto de una torre en París en la intersección de la rue Montmartre y el bulevar Montmartre . Esta señal de la torre estaba a cargo de una mujer policía y ella operaba una caja de metal giratoria de cuatro lados en la parte superior de una vitrina de vidrio donde la palabra "Alto" estaba pintada en rojo y la palabra "Adelante" pintada en blanco. [21]
Eléctrico
Un semáforo eléctrico fue desarrollado en 1912 por Lester Wire , un policía de Salt Lake City , Utah , que también usaba luces rojas y verdes. [22] El 5 de agosto de 1914, la American Traffic Signal Company instaló un sistema de señales de tráfico en la esquina de East 105th Street y Euclid Avenue en Cleveland , Ohio. [23] [24] Tenía dos colores, rojo y verde, y un timbre , basado en el diseño de James Hoge, para advertir de los cambios de color. El diseño de James Hoge [25] permitió a la policía y las estaciones de bomberos controlar las señales en caso de emergencia . El primer semáforo de cuatro vías y tres colores fue creado por el oficial de policía William Potts en Detroit , Michigan en 1920. [26] Ashville , Ohio afirma ser el hogar del semáforo en funcionamiento más antiguo de los Estados Unidos, utilizado en un intersección de vías públicas desde 1932 hasta 1982 cuando se trasladó a un museo local. [27] [28] Muchas imágenes de semáforos históricos aparecen en una página de Trivia de señales de tráfico. [29]
La torre fue la primera innovación que utilizó el semáforo de tres colores y apareció por primera vez en la ciudad de Detroit , donde se construyó el primer semáforo de tres colores en la intersección de las avenidas Michigan y Woodward en 1920. El hombre detrás de este tres- El semáforo en color era el oficial de policía William Potts de Detroit. Le preocupaba cómo los agentes de policía en cuatro señales de luces diferentes no podían cambiar sus luces al mismo tiempo. La respuesta fue una tercera luz de color ámbar, que era el mismo color que se usa en el ferrocarril. [14] Potts también colocó un temporizador con la luz para ayudar a coordinar un conjunto de luces de cuatro vías en la ciudad. La torre de tráfico pronto usó doce focos para controlar el tráfico y la razón de una torre en primer lugar fue que en ese momento la intersección era una de las más transitadas del mundo, con más de 20,000 vehículos diarios. [30]
Los Ángeles instaló sus primeros semáforos automáticos en octubre de 1920 en cinco ubicaciones de Broadway. Estas primeras señales, fabricadas por Acme Traffic Signal Co., emparejaron los brazos del semáforo "Stop" y "Go" con pequeñas luces rojas y verdes. Las campanas desempeñaron el papel de las luces ámbar de hoy, sonando cuando las banderas cambiaron, un proceso que tomó cinco segundos. Para 1923, la ciudad había instalado 31 dispositivos de control de tráfico Acme. [31] Los semáforos de semáforo de Acme se usaban a menudo en los dibujos animados de Warner Bros. Looney Tunes y Merrie Melodies para obtener un efecto cómico debido a su fuerte campana.
El primer sistema de señales de tráfico interconectado se instaló en Salt Lake City en 1917, con seis intersecciones conectadas controladas simultáneamente con un interruptor manual. [32] El control automático de los semáforos interconectados se introdujo en marzo de 1922 en Houston , Texas . [33]
En 1922, las torres de tráfico comenzaban a ser controladas por temporizadores automáticos. La primera empresa en agregar temporizadores en los semáforos fue Crouse Hinds. Construyeron señales de ferrocarril y fueron la primera empresa en colocar temporizadores en los semáforos en Houston , que era su ciudad natal. [34] La principal ventaja del uso del temporizador fue que ahorró dinero a las ciudades al reemplazar a los oficiales de tránsito. La ciudad de Nueva York pudo reasignar a todos menos 500 de sus 6.000 oficiales que trabajaban en la brigada de tráfico; esto le ahorró a la ciudad $ 12,500,000. [34]
Después de presenciar un accidente entre un automóvil y un carruaje tirado por caballos, el inventor Garrett Morgan presentó una patente estadounidense para una señal de tráfico. [35] La patente nº 1.475.024 [36] se concedió el 20 de noviembre de 1923 para el semáforo de tres posiciones de Morgan.
Los primeros semáforos en Gran Bretaña se instalaron en Piccadilly Circus en 1926. [37] Wolverhampton fue la primera ciudad británica en introducir semáforos automáticos en 1927 en Princes Square en el cruce de Lichfield Street y Princess Street. [38]
Melbourne fue la primera ciudad de Australia en instalar semáforos en 1928 en la intersección de Collins y Swanston Street.
El sistema de doce luces no estuvo disponible hasta 1928 y otra característica del sistema de iluminación fue que se colocaron capuchas sobre la luz y se pulió con chorro de arena cada lente para aumentar la visibilidad diurna. [39]
Tanto la torre como los semáforos se eliminaron gradualmente en 1930. Las torres eran demasiado grandes y obstruían el tráfico; los semáforos eran demasiado pequeños y los conductores no podían verlos por la noche. [20]
En 1949, el primer semáforo del continente asiático se instaló en Haifa , Israel . [40]
El primer semáforo en el sur de la India se instaló en Egmore Junction, Chennai en 1953. La ciudad de Bangalore instaló su primer semáforo en Corporation Circle en 1963. [41]
El control de los semáforos dio un gran giro con el auge de las computadoras en Estados Unidos en la década de 1950.
Gracias a las computadoras, el cambio de luces hizo que el flujo de Crosby fuera aún más rápido gracias a la detección computarizada. Se colocó una placa de presión en las intersecciones para que una vez que un automóvil estuviera en la placa, las computadoras supieran que había un automóvil esperando en el semáforo en rojo. [42] Algo de esta detección incluyó conocer el número de autos en espera contra la luz roja y el tiempo que esperó el primer vehículo en la roja. [43] Uno de los mejores ejemplos históricos de control computarizado de luces fue en Denver en 1952. Una computadora tomó el control de 120 luces con seis detectores sensibles a la presión que miden el tráfico entrante y saliente. El sistema estaba instalado en el distrito comercial central, donde la mayor parte del tráfico se encontraba entre el centro de la ciudad y las partes norte y noreste de la ciudad. La sala de control que albergaba la computadora a cargo del sistema estaba en el sótano del edificio de la ciudad y el condado. [43] A medida que las computadoras comenzaron a evolucionar, el control de los semáforos también mejoró y se hizo más fácil. En 1967, la ciudad de Toronto fue la primera en utilizar computadoras más avanzadas que eran mejores en la detección de vehículos. [43] Gracias a las nuevas y mejores computadoras, el flujo de tráfico se movió incluso más rápido que con el uso de la torre. Las computadoras mantuvieron el control de 159 señales en las ciudades a través de líneas telefónicas. La gente elogió a las computadoras por su capacidad de detección. Gracias a la detección, los ordenadores pudieron cambiar la duración de la luz verde en función del volumen de coches en espera. [44] El auge de las computadoras es el modelo de control del tráfico que se utiliza ahora en el siglo XXI.
Los temporizadores de cuenta regresiva en los semáforos se introdujeron en la década de 1990. Los temporizadores son útiles para los peatones, para planificar si hay tiempo suficiente para cruzar la intersección antes del final de la fase de caminata, y para los conductores, para saber la cantidad de tiempo antes de que se encienda la luz. En los Estados Unidos, los temporizadores para el tráfico de vehículos están prohibidos, pero ahora se requieren temporizadores para peatones en señales nuevas o mejoradas en carreteras más anchas. En algunas ciudades, incluida Filadelfia , los automovilistas también pueden utilizar los temporizadores para peatones para saber cuánto tiempo queda en el ciclo verde, porque cuando el temporizador para peatones llega a cero, la señal se volverá ámbar simultáneamente.
Tipos y colocación de colores.
Un semáforo vertical típico tiene tres aspectos, o semáforos, frente al tráfico que se aproxima, rojo arriba, ámbar abajo y verde debajo. Generalmente se ilumina un aspecto a la vez. En algunos casos, un cuarto aspecto, para una flecha de giro, por ejemplo, está debajo de los tres semáforos o aspectos en intersecciones de tráfico vial más complicadas.
Aspectos únicos
El semáforo más simple comprende uno o dos aspectos de color que advierten a cualquier usuario del derecho de paso compartido de un posible conflicto o peligro.
- Rojo intermitente: tratado como una señal de alto . Esto también puede indicar que la carretera está cerrada. En Francia y el Reino Unido, el rojo intermitente exige una parada absoluta, en el cruce de una línea de ferrocarril, una pista de aeropuerto, un puente giratorio o una estación de bomberos.
- Ámbar intermitente: precaución, cruce o peligro en la carretera más adelante.
- Verde intermitente: varía según la jurisdicción. El verde intermitente puede dar permiso para seguir recto y girar a la izquierda frente al tráfico opuesto (que se detiene con una luz roja fija), puede indicar el final de un ciclo verde antes de que la luz cambie a ámbar fijo o ( como en Columbia Británica, Canadá o Ciudad de México, México) indica que la intersección es un paso de peatones.
En los Estados Unidos, las luces intermitentes rojas o ámbar, conocidas como balizas de control de intersecciones , se utilizan para reforzar las señales de alto en las intersecciones. [45]
Aspectos duales
Estos tienen dos luces, generalmente montadas verticalmente. A menudo se ven en cruces de ferrocarril, estaciones de bomberos e intersecciones de calles. Parpadean en ámbar o blanco cuando no se espera tráfico cruzado, y se vuelven rojas para detener el tráfico cuando ocurre tráfico cruzado (por ejemplo, los camiones de bomberos están a punto de salir de la estación). A veces también se utilizan para la medición de rampas , donde los automovilistas ingresan a una carretera de acceso controlado durante el tráfico pesado. Por lo general, solo un vehículo en la rampa avanza cuando la señal se muestra en verde. En algunos casos se permiten dos o tres por green.
Tres o más aspectos y posicionamiento de aspectos
La señal de tráfico estándar es la luz roja sobre la verde, con ámbar en medio.
Cuando la señal de tráfico con tres aspectos está dispuesta horizontal o lateralmente, la disposición depende de la regla de la carretera . En los países del carril derecho, la secuencia (de izquierda a derecha) es rojo-ámbar-verde. [ cita requerida ] En los países del carril izquierdo, la secuencia es verde-ámbar-rojo. [ cita requerida ]
Algunas veces se agregan otras señales para un mayor control, como para el transporte público y los giros a la derecha o izquierda se permiten solo cuando la flecha verde está iluminada o específicamente prohibidos si la flecha roja está iluminada.
Ciclos de señales de tráfico
Generalmente, al menos una dirección del tráfico en una intersección tiene las luces verdes (aspecto verde) en cualquier momento del ciclo. En algunas jurisdicciones, durante un breve período de tiempo, todas las señales en una intersección se muestran en rojo al mismo tiempo para despejar el tráfico en la intersección. El retraso puede depender del tráfico, las condiciones de la carretera, el diseño físico de la intersección y los requisitos legales. Por lo tanto, las señales modernas se construyen para permitir el "todo rojo" en una intersección, incluso si la función no se utiliza.
Algunas señales no tienen una fase "completamente roja": la luz se vuelve verde para el tráfico cruzado en el instante en que la otra luz se pone roja. [nota 1]
Otra variante en algunos lugares es la lucha de peatones , donde todos los semáforos de los vehículos se vuelven rojos y los peatones pueden caminar libremente, incluso en diagonal, a través de la intersección.
Variaciones
En la provincia canadiense de Quebec y las provincias marítimas, las luces a menudo están dispuestas horizontalmente, pero cada aspecto tiene una forma diferente: el rojo es un cuadrado (más grande que el círculo normal) y generalmente en pares en cada extremo del accesorio, el ámbar es un diamante y verde es un círculo. En muchos estados del sur y suroeste de EE. UU., La mayoría de las señales de tráfico son igualmente horizontales para aliviar la resistencia del viento durante tormentas y huracanes. [46]
Las señales de tráfico japonesas siguen en su mayoría la misma regla, excepto que las señales de "continuar" se denominan 青 ( azul ), que históricamente eran de hecho, pero esto causó complicaciones con la regla internacional "verde para continuar", por lo que [47] en 1973 se emitió un decreto por el que la luz "go" debería cambiarse al tono de verde más azul posible, haciéndola así más ecológica sin tener que cambiar el nombre de 青 (azul) a 緑 (verde).
En Gran Bretaña, los semáforos normales siguen esta secuencia: [48]
- Rojo: deténgase, no continúe
- Rojo y ámbar: prepárese para continuar, pero no continúe todavía
- Verde: continúe si la intersección o el cruce está despejado, no se le permite bloquear la intersección o el cruce
- Ámbar: deténgase, a menos que no sea seguro hacerlo.
Uso de señales de tráfico en vías navegables, en vías férreas para el tráfico ferroviario
El estándar de tres aspectos también se utiliza en las esclusas del río Upper Mississippi . El rojo significa que está atravesando otro recipiente. Ámbar significa que la cámara de la esclusa se vacía o se llena para igualar el nivel del recipiente que se aproxima. Después de que se abre la puerta, verde significa que la embarcación puede entrar.
Las señales de ferrocarril, para detener los trenes en su propio derecho de paso, utilizan la posición opuesta de los colores; los dos tipos no se pueden confundir. [ cita requerida ] Es decir, el verde en la parte superior y el rojo en la parte inferior es la ubicación estándar de los colores de las señales en las vías del tren.
Luces de cruce de peatones y ciclistas
Australia y Nueva Zelanda
En Australia y Nueva Zelanda, la secuencia de luces para peatones es:
- Hombre verde: seguro para cruzar la intersección
- Hombre rojo intermitente: continúe cruzando si ya está en la intersección, pero no comience a cruzar
- Hombre rojo: no cruces
Algunos semáforos en las capitales (por ejemplo , Sydney , Melbourne , Brisbane , Perth y Adelaide ) tienen temporizadores de cuenta regresiva para los semáforos de peatones, generalmente una cuenta regresiva desde el 30 cuando apareció el hombre rojo intermitente. Se han instalado temporizadores de cuenta regresiva en algunas luces de cruce de peatones en Auckland y Christchurch, contando desde 15 segundos.
Algunos cruces controlados por semáforos tienen una secuencia de luces que detiene todo el tráfico vehicular en el cruce al mismo tiempo y les da a los peatones acceso exclusivo a la intersección para que puedan cruzar en cualquier dirección (incluso en diagonal). Esto se presenta de manera destacada en el distrito financiero de Sydney, fuera del ayuntamiento, y en otros lugares donde los peatones abundan, como Redfern, cerca de la Universidad de Sydney. Esto se conoce como lucha de peatones o baile de Barnes en algunos lugares. En Nueva Zelanda, estos pasos de peatones se pueden encontrar en el distrito central de negocios (CBD) de Auckland , Wellington , Christchurch y Dunedin .
The Barnes Dance lleva el nombre de un ingeniero de tráfico estadounidense, Henry A. Barnes. Barnes no afirmó haber inventado el sistema, pero fue un firme defensor de él, habiendo observado las dificultades que enfrentó su hija al cruzar la calle para llegar a la escuela. [49]
Varias intersecciones en Wellington, Nueva Zelanda, tienen figuras alternativas del hombre verde. Ocho intersecciones cerca de los edificios del Parlamento tienen siluetas de la sufragista Kate Sheppard , [50] mientras que cuatro intersecciones a lo largo de la calle Cuba tienen siluetas de la artista drag y activista por los derechos LGBT Carmen Rupe . [51]
Asia
La secuencia de luz china es:
- Verde: seguro para cruzar.
- Rojo: no cruce.
- Ámbar (fijo, después del verde, antes del rojo): continúe cruzando solo si no puede detenerse de manera segura.
- Ámbar intermitente: cruce con precaución (se usa a menudo en cruces de poco tráfico o después de la medianoche).
La secuencia de semáforos de peatones japoneses es:
- Hombre caminando azul / verde: seguro para cruzar; los ciclistas pueden cruzar o girar a la izquierda en la dirección del tráfico.
- Hombre caminando azul / verde intermitente: no empiece a cruzar; Termine de cruzar o regrese a la acera.
- Hombre de pie rojo: no cruces
Para obtener más información sobre la situación en Japón, consulte日本 の 音響 装置 付 信号 機 (en japonés) .
Europa
El enfoque europeo para un cruce señalizado es utilizar un aspecto dual o, más raramente, triple [52] con una lente oscurecida de un peatón pictograma . Para los ciclistas, se utiliza el mismo enfoque, con la lente oscurecida para un cuadro de bicicleta. No es raro ver lentes con ambos símbolos. La mayoría de los países europeos usan naranja en lugar de ámbar para la luz media.
La secuencia de luces del ciclista es:
- Verde: seguro para cruzar.
- Ámbar: continúe cruzando solo si no puede detenerse de manera segura.
- Ámbar intermitente: cruce con precaución (se usa a menudo cuando las luces no funcionan o se apagan).
- Rojo: no cruce.
En Alemania, la República Checa y algunos otros países de Europa Central, una combinación de luces rojas y naranjas se ilumina justo antes de la fase verde. La secuencia de luces del ciclista es la siguiente: [ cita requerida ]
- Verde: seguro para cruzar.
- Naranja: continúe cruzando solo si no puede detenerse de manera segura.
- Naranja intermitente: cruce con precaución, obedezca la señalización (se usa cuando las luces no funcionan o se apagan).
- Rojo: no cruce.
- Rojo y naranja: no cruces, prepárate para el verde.
La luz está oscurecida con un pictograma de peatón.
Los semáforos para peatones de Ampelmännchen se han convertido en una señal nostálgica de la antigua República Democrática Alemana . En Alemania, la multa por cruzar un semáforo en rojo si es atrapado es a partir de 2019 entre 5 y 10 €. [53]
En el Reino Unido, Irlanda, dependencias de la Corona británica y territorios dependientes, y antiguas posesiones como Hong Kong, se muestran a los peatones dos o más de las siguientes señales:
- Una imagen fija de una persona que camina verde: cruce la calle
- Persona que camina en verde intermitente: continúe cruzando si ya está en el cruce, pero no comience a cruzar. Algunas señales utilizan una pantalla de cuenta atrás numérica de color ámbar, en lugar del hombre verde intermitente, que indica a los peatones el tiempo que queda para cruzar la calle. [54]
- Hombre de pie rojo: no cruzar / no empezar a cruzar
En el Reino Unido no se comete una infracción directa si un peatón no obedece las señales de cruce y muchos semáforos generalmente solo usan dos imágenes fijas: una persona que camina en verde y un hombre de pie rojo, siendo este el caso general cuando el cruce es en una carretera. El cruce y las señales para peatones están en combinación con las que controlan el tráfico vehicular. Las luces intermitentes de color ámbar y las imágenes en los cruces de peatones se utilizan cuando los semáforos de vehículos realizan la única función de detener el tráfico de la carretera para permitir que los peatones crucen una calle.
El mismo sistema se utiliza también en Suiza , Hong Kong y Macao .
América del norte
En los Estados Unidos, el aspecto más común es el escrito "caminar" o "no caminar". En Canadá, la persona blanca que camina casi siempre se usa. Cada vez más para las modificaciones de aspectos duales e instalaciones más nuevas, el aspecto inferior que se usaba anteriormente para la señal de "caminar" (una persona que camina) está siendo reemplazado por un temporizador de cuenta regresiva. El pictograma de la mano levantada apareció por primera vez en la ciudad de Westmount, Montreal, y fue inventado por Alexander Heron, después de haber observado la mano enguantada de un policía que controlaba un cruce. [ cita requerida ]
La secuencia de luces es:
- Persona que camina o "camina" verde, azul o blanca: cruce con precaución (los peatones tienen el derecho de paso; los automovilistas que giran a la izquierda oa la derecha deben ceder el paso a los peatones).
- Parpadeando en rojo o naranja, pare la mano o "no camine": no comience a cruzar, pero continúe si ya está en el medio de la intersección.
- Detenga la mano roja o naranja o "no camine": no ingrese a la intersección.
El estado estadounidense de Massachusetts permite una variación de indicación inusual para el movimiento de peatones. En las intersecciones señalizadas sin semáforos para peatones separados, las señales de tráfico pueden programarse para que se pongan rojas en todas las direcciones, seguidas de una exhibición fija de luces ámbar simultáneamente con las indicaciones rojas. Durante esta indicación de rojo más ámbar, la intersección está cerrada al tráfico de vehículos y los peatones pueden cruzar, generalmente en la dirección que elijan (esto se conoce como " baile de Barnes "). [ cita requerida ]
Señales auditivas y táctiles para personas discapacitadas
En algunas jurisdicciones, como Australia, Nueva Zelanda, los Países Bajos e Irlanda, las luces para peatones están asociadas con un dispositivo de sonido, en beneficio de los peatones ciegos y con discapacidad visual. Éstos emiten un pitido lento cuando las luces para peatones están en rojo y un zumbido continuo o un pitido rápido cuando las luces están en verde. En los estados australianos de Queensland , Nueva Gales del Sur , Victoria y Australia Occidental , el sonido se produce en la misma unidad que los botones pulsadores. En un círculo sobre el botón, se produce el sonido y se puede sentir junto con una flecha levantada que apunta en la dirección a caminar. [55] Este sistema de tecnología de asistencia también se usa ampliamente en intersecciones concurridas en ciudades canadienses.
En el Reino Unido, los cruces Puffin y su predecesor, el cruce Pelican , emitirán un pitido rápido para indicar que es seguro cruzar la carretera. El pitido se desactiva durante la noche para no molestar a los residentes cercanos. [56]
En algunos estados de los Estados Unidos, en algunas intersecciones con mucho tráfico, los botones emitirán un pitido para las personas ciegas. Cuando cambia la luz, un altavoz integrado en el botón reproducirá una grabación para notificar a las personas ciegas que es seguro cruzar. Cuando la señal parpadee en rojo, la grabación comenzará a contar hacia atrás con el temporizador de cuenta regresiva.
En varios países, como Nueva Zelanda, la tecnología también permite que las personas sordas y ciegas sientan cuando las luces han cambiado para permitir un cruce seguro. Una pequeña almohadilla, alojada dentro de una hendidura en la base de la caja que alberga el mecanismo del botón, se mueve hacia abajo cuando las luces cambian para permitir el cruce. Esto está diseñado para que lo sienta cualquier persona que esté esperando para cruzar y que tenga una capacidad limitada para detectar la vista o el sonido.
En Japón, un semáforo emite un sonido electrónico que imita el canto de los pájaros para ayudar a las personas con discapacidad visual. Algunos semáforos fijan el orden y el tipo de sonido para que puedan saber en qué dirección se encuentra una luz verde. En general, "Piyo" (pío) y "Piyo-piyo", que es una llamada de pájaro pequeño, y "Kakkō" y "Ka-kakkō", que es una llamada de cuco, están asociados con este sistema. [57]
Luces para transporte público
Traffic lights for public transport often use signals that are distinct from those for private traffic. They can be letters, arrows or bars of white or coloured light.
In Portland, Oregon, the tram signals feature an orange horizontal bar and a white vertical bar.[citation needed] Some systems use the letter B for buses, and T for trams.
In some European countries and Russia, dedicated traffic signals for public transport (tram, as well any that is using a dedicated lane) have four white lights that form the letter T.[citation needed] If the three top lamps are lit, this means "stop". If the bottom lamp and some lamps on the top row are lit, this means permission to go in a direction shown. In case of a tram signal, if there are no tram junctions or turns on an intersection, a simpler system of one amber signal in the form of letter T is used instead; the tram must proceed only when the signal is lit.
In North European countries, the tram signals feature white lights of different forms: "S" for "stop", "—" for "caution" and arrows to permit passage in a given direction.[58]
The Netherlands use a distinctive "negenoog" (nine-eyed) design shown on the top row of the diagram;[59] bottom row signals are used in Belgium, Luxembourg, France and Germany. The signals mean (from left to right): "go straight ahead", "go left", "go right", "go in any direction" (like the "green" of a normal traffic light), "stop, unless the emergency brake is needed" (equal to "amber"), and "stop" (equal to "red").
The METRO light rail system in Minneapolis, Minnesota, the Valley Metro Rail in Phoenix, Arizona, and the RTA Streetcar System in New Orleans use a simplified variant of the Belgian/French system in the respective city's central business district where only the "go" and "stop" configurations are used. A third signal equal to amber is accomplished by flashing the "go" signal.
In Japan, tram signals are under the regular vehicle signal; however, the colour of the signal intended for trams is orange.
In Hong Kong Island, Hong Kong, an amber T-signal is used for trams, in place of the green signal. Addition to that, at any tramway junction, another set of signals is available to indicate the direction of the tracks.
In Australia and New Zealand, a white "B" or "T" sometimes replaces the green light indicating that buses or trams (respectively) have right of way.
Preemption and priority
Some regions have signals that are interruptible, giving priority to special traffic usually emergency vehicles such as fire apparatus, ambulances, and police squad cars.[60][61] Most of the systems operate with small transmitters that send radio waves, infrared signals, or strobe light signals that are received by a sensor on or near the traffic lights. Some systems use audio detection, where a certain type of siren must be used and detected by a receiver on the traffic light structure.
Upon activation, the normal traffic light cycle is suspended and replaced by the "preemption sequence": the traffic lights to all approaches to the intersection are switched to "red" with the exception of the light for the vehicle that has triggered the preemption sequence. Sometimes, an additional signal light is placed nearby to indicate to the preempting vehicle that the preempting sequence has been activated and to warn other motorists of the approach of an emergency vehicle. The normal traffic light cycle resumes after the sensor has been passed by the vehicle that triggered the preemption.
In lieu of preemptive mechanisms, in most jurisdictions, emergency vehicles are not required to respect traffic lights. However, emergency vehicles must slow down, proceed cautiously and activate their emergency lights to alert oncoming drivers to the preemption when crossing an intersection against the light.[62][63]
Unlike preemption, which immediately interrupts a signal's normal operation to serve the preempting vehicle and is usually reserved for emergency use, "priority" is a set of strategies intended to reduce delay for specific vehicles, especially mass transit vehicles such as buses. A variety of strategies exist to give priority to transit but they all generally work by detecting approaching transit vehicles and making small adjustments to the signal timing. These adjustments are designed to either decrease the likelihood that the transit vehicle will arrive during a red interval or decrease the length of the red interval for those vehicles that are stopped. Priority does not guarantee that transit vehicles always get a green light the instant they arrive like preemption does.
Girar señales y reglas
In some instances, traffic may turn left (in jurisdictions with left-hand traffic) or right (in jurisdictions with right-hand traffic) after stopping at a red light, providing they give way to the pedestrians and other vehicles. In some places that generally disallow this, a sign next to the traffic light indicates that it is allowed at a particular intersection.[64] Conversely, jurisdictions that generally allow this might forbid it at a particular intersection with a "no turn on red" sign, or put a green arrow to indicate specifically when a turn is allowed without having to yield to pedestrians (this is usually when traffic from the perpendicular street is making a turn onto one's street and thus no pedestrians are allowed in the intersection anyway). Some jurisdictions allow turning on red in the opposite direction (left in right-driving countries; right in left-driving countries) from a one-way road onto another one-way road; some of these even allow these turns from a two-way road onto a one-way road.[65] Also differing is whether a red arrow prohibits turns; some jurisdictions require a "no turn on red" sign in these cases. A study in the State of Illinois (a right-driving jurisdiction) concluded that allowing drivers to proceed straight on red after stopping, at specially posted T-intersections where the intersecting road went left only, was dangerous.[citation needed] Proceeding straight on red at T-intersections where the intersecting road went left only used to be legal in Mainland China, with right-hand traffic provided that such movement would not interfere with other traffic, but when the Road Traffic Safety Law of the People's Republic of China took effect on 1 May 2004, such movement was outlawed.[66] In some other countries, the permission is indicated by a flashing amber arrow (cars do not have to stop but must give way to other cars and pedestrians) in Western Europe, or by a green arrow at the same height as the full red light (whether cars have to stop depends on the country) in Central Europe.
Another distinction is between intersections that have dedicated signals for turning across the flow of opposing traffic and those that do not. Such signals are called dedicated left-turn lights in the United States and Canada (since opposing traffic is on the left). With dedicated left turn signals, a left-pointing arrow turns green when traffic may turn left without opposing traffic and pedestrian conflict, and turns red or disappears otherwise. Such a signal is referred to as a "protected" signal if it has its own red phase; a "permissive" signal does not have such a feature. Three standard versions of the permissive signal exist:[citation needed] One version is a horizontal bar with five lights – the green and amber arrows are located between the standard green and amber lights. A vertical five-light bar holds the arrows underneath the standard green light (in this arrangement, the amber arrow is sometimes omitted, leaving only the green arrow below the steady green light, or possibly an LED based device capable of showing both green and amber arrows within a single lamp housing). Some newer LED turn arrows seen in parts of Canada are capable of multicoloured animation. Such lights will often display a flashing and animated green or amber arrow when the dedicated turn is allowed, but then transform into a red arrow on a white background with a red line through it, emphasising that the turn is no longer allowed. These lights will also often have the words "no turn" displayed, or an explanatory reason why the turn is not allowed, such as "train" in the case of a rail or light rail crossing. A third type is known as a "doghouse" or "cluster head" – a vertical column with the two normal lights is on the right side of the signal, a vertical column with the two arrows is located on the left, and the normal red signal is in the middle above the two columns. Cluster signals in Australia and New Zealand use six signals, the sixth being a red arrow that can operate separately from the standard red light. In a fourth type, sometimes seen at intersections in Ontario and Quebec, Canada, there is no dedicated left-turn lamp per se. Instead, the normal green lamp flashes rapidly, indicating permission to go straight as well as make a left turn in front of opposing traffic, which is being held by a steady red lamp. (This "advance green," or flashing green can be somewhat startling and confusing to drivers not familiar with this system. This also can cause confusion amongst visitors to British Columbia, where a flashing green signal denotes a pedestrian controlled crosswalk. For this reason, Ontario is phasing out the use of flashing green signals and instead replacing them with arrows.)[67][68] Another interesting practice seen at least in Ontario is that cars wishing to turn left that arrived after the left turn signal ended can do so during the amber phase, as long as there is enough time to make a safe turn.[69]
A flashing amber arrow, which allows drivers to make left turns after giving way to oncoming traffic, is becoming more widespread in the United States, particularly in Oregon, North Carolina, Virginia, Michigan (replacing their trademark "red-ball" flashing left-turn lights), and Las Vegas, Nevada.[citation needed] In the normal sequence, a protected green left-turn arrow will first change to a steady amber arrow to indicate the end of the protected phase, then to a flashing amber arrow, which remains flashing until the standard green light changes to amber and red. These generally take the form of four signal sections (green, amber, amber arrow, red). On some newer signals, notably in the city of Bend, Oregon, the green and flashing amber arrows emanate from the same light section through the use of a dual-colour LED array, while the steady amber arrow is mounted above it. In Las Vegas, the arrow turns flashing amber from a red light, before turning red again.[citation needed]
Generally, a dedicated left-turn signal is illuminated at the beginning of the green phase of the green-amber-red-green cycle. This is called a leading turn. This allows left-turn traffic, which often consists of just a few cars, to vacate the intersection quickly before giving priority to vehicles traveling straight. This increases the throughput of left-turn traffic while reducing the number of drivers, perhaps frustrated by long waits in heavy traffic for opposing traffic to clear, attempting to make an illegal left turn on red. A dedicated left-turn signal that appears at the end of the green phase is called a lagging turn. If there is no left-turn signal, the law requires one to yield to oncoming traffic and turn when the intersection is clear and it is safe to do so. In the U.S., many older inner-city and rural areas do not have dedicated left-turn lights, while most newer suburban areas have them. Such lights tend to decrease the overall efficiency of the intersection as it becomes congested, although it makes intersections safer by reducing the risk of head-on collisions and may even speed up through traffic, but if a significant amount of traffic is turning, a dedicated turn signal helps eliminate congestion.
Some intersections with permissive turn signals occasionally have what is known as "yellow trap", "lag-trap", or "left turn trap" (in right-driving countries).[citation needed] This refers to situations when left-turning drivers are trapped in the intersection with a red light, while opposing traffic still has a green. In British Columbia, the law addresses this problem by giving a left-turning driver already in an intersection the right-of-way to make the turn once the intersection is otherwise clear, regardless of the traffic light state.
For example, an intersection has dedicated left-turn signals for traffic traveling north. The southbound traffic gets a red light so northbound traffic can make a left turn, but the straight-through northbound traffic continues to get a green light. A southbound driver who had entered the intersection earlier will now be in a predicament, since they have no idea whether traffic continuing straight for both directions is becoming red, or just their direction. The driver will now have to check the traffic light behind them, which is often impossible from the viewing angle of a driver's seat. This can also happen when emergency vehicles or railroads preempt normal signal operation. [70] In the United States, signs reading "Oncoming traffic has extended green" or "Oncoming traffic may have extended green" must be posted at intersections where the "yellow trap" condition exists.[71][72]
Although motorcycles and scooters in most jurisdictions follow the same traffic signal rules for left turns as do cars and trucks, some places, such as Taiwan, have different rules. In these areas, it is not permitted for such small and often hard-to-see vehicles to turn left in front of oncoming traffic on certain high-volume roads when there is no dedicated left-turn signal.[citation needed] Instead, in order to make a left turn, the rider moves to the right side of the road, travels through the first half of the intersection on green, then slows down and stops directly in front of the line of cars on the driver's right waiting to travel across the intersection, which are of course being held by a red light. There is often a white box painted on the road in this location to indicate where the riders should group.[citation needed] The rider turns the bike 90 degrees to the left from the original direction of travel and proceeds along with the line of cars when the red light turns green, completing the left turn. This procedure improves safety because the rider never has to cross oncoming traffic, which is particularly important given the much greater likelihood of injury when a cycle is hit by a car or truck. This system (called a "hook turn") is also used at many intersections in the central business district (CBD) of Melbourne, Australia, where either or both streets carry tramways. This is done so right-turning vehicles (Australia drives on the left) do not block the passage of trams. The system is being extended to the suburbs.
Control de carril
Lane-control lights are a specific type of traffic light used to manage traffic on a multi-way road, highway or tollway. Typically, these lights allow or forbid traffic to use one or more of the available lanes by the use of green lights or arrows (to permit) or by red lights or crosses (to prohibit). In the US, lane-control lights are often used to control and/or direct the flow of traffic through toll plazas and highway tunnels, such as during unusually-heavy traffic flow when more lanes may be required in one direction than in the other direction, or during a hurricane evacuation, when the lane signals for most or all lanes will show green for one direction to assist in more rapid traffic flow from the evacuation site. Lane-control lights are also used at highway weigh stations to direct tractor-trailers and other heavy or oversized vehicles into the proper lanes for weighing, inspection or exit.
In the US, most notably the Southeastern, there often is a "continuous-flow" lane. This lane is protected by a single, constant-green arrow pointing down at the lane(s) permitting the continuous flow of traffic, without regard to the condition of signals for other lanes or cross streets. Continuous lanes are restricted in that vehicles turning from a side street may not cross over the double white line to enter the continuous lane, and no lane changes are permitted to the continuous lane from an adjacent lane or from the continuous lane to an adjacent lane, until the double white line has been passed. Some continuous lanes are protected by a raised curb located between the continuous lane and a normal traffic lane, with white and/or amber reflective paint or tape, prohibiting turning or adjacent traffic from entering the lane. Continuous-flow traffic lanes are found only at "T" intersections where there is no side street or driveway entrance on the right side of the main thoroughfare; additionally, no pedestrians are permitted to cross the main thoroughfare at intersections with a continuous-flow lane, although crossing at the side street may be permitted. Intersections with continuous-flow lanes will be posted with a white regulatory sign approximately 500 ft (150 m) before the intersection with the phrase, "right lane continuous traffic," or other, similar, wording. If the arrow is extinguished for any reason, whether by malfunction or design, traffic through the continuous lane will revert to the normal traffic pattern for adjacent lanes, except that turning or moving into or out of the restricted lane is still prohibited.
Señal de velocidad
A speed sign is a special traffic light, variable traffic sign or variable-message sign giving drivers a recommended speed to approach the next traffic light in its green phase[73] and avoid a stop due reaching the intersection when lights are red.[74][note 2][clarification needed]
Provisiones especiales
Traffic light failure in most jurisdictions in Australia and countries in Europe must be handled by drivers as a priority-to-the-right intersection, or an all-way stop elsewhere, pending the arrival of a police officer to direct traffic. In Armenia, Belarus, Belgium, Bosnia and Herzegovina, Croatia, Czech Republic, Estonia, France, Georgia, Germany, Greece, Iceland, Italy, Kazakhstan, Kosovo, Latvia, Lithuania, Luxembourg, Moldova, Netherlands, Poland, Portugal, Romania, Russia, Serbia, Slovakia, Slovenia, Sweden, Switzerland (and Liechtenstein), Turkey, and Ukraine, traffic lights may have additional right-of-way signs mounted above, below or next to the traffic lights; these take effect when the lights are no longer active or are flashing amber. A flashing amber traffic light usually indicates you have a yield or stop sign as a redundant sign, while a turned off traffic light usually indicates you have the right-of-way. In the UK and parts of North America, drivers simply treat the junction as being uncontrolled when traffic lights fail, giving way as appropriate, unless a police officer is present. In much of the United States failed traffic signals must be treated as all-way stop intersections.
In the US, traffic lights inactive at nighttime emit an amber-coloured flashing signal in directions owing priority while the intersecting street emit a flashing red light, requiring drivers to stop before proceeding.[citation needed]
Luces simuladas
In an era when intersections were often controlled by a single traffic signal head, many signals were installed on pedestals in the centers of intersections. Often referred to as "dummy lights," these installations often replaced beacons or "mushrooms" that denoted the centers of intersections and separated opposing traffic, with the infrastructure used for the beacons and mushrooms serving the new "stop and go" type signals.[citation needed]
There are a handful of operational dummy lights still in service. Three are located in New York State: Beacon, Canajoharie and Croton-on-Hudson.[75]
After a dummy light was knocked down by a truck in 2010, the city of Coleman, Texas decided to preserve and refurbish its last two pedestal mounted dummy lights as part of its historic district preservation efforts.[citation needed]
In 2011, the Arkansas State Historic Preservation Office nominated the state's last remaining pedestal mounted signal, located in Smackover, to be listed on the National Register of Historic Places.[citation needed]
The oldest working 'dummy' style beacon in Rhode Island was located in the Historic Mill village of Albion in the Blackstone River Valley (town of Lincoln, RI). It was erected in 1932 above where the old village well stood in the center square. In April 2015 it was destroyed by a motorist. The beacon was a local historical site and the logo for a local Boy Scout Troop, Troop 711 Albion.
Increases in traffic flows have prompted calls for these types of traffic lights to be removed due to safety concerns, but their historic value has kept these landmarks at their original locations. To serve historic district applications, Teeco Safety Systems of Shreveport, Louisiana, still manufactures replacement fixed 4-way traffic signals for pedestal and overhead span wire installations.[76]
Tecnología
Optics and lighting
Traditionally, incandescent and halogen bulbs were used[where?]. Because of the low efficiency of light output and a single point of failure (filament burnout) municipalities[where?] are retrofitting traffic signals with LED arrays that consume less power, have increased light output, last significantly longer.[citation needed] Moreover, in the event of an individual LED failure, the aspect will still operate albeit with a reduced light output. The light pattern of an LED array can be comparable to the pattern of an incandescent or halogen bulb fitted with a prismatic lens.
The low energy consumption of LED lights can pose a driving risk in some areas during winter. Unlike incandescent and halogen bulbs, which generally get hot enough to melt away any snow that may settle on individual lights, LED displays – using only a fraction of the energy – remain too cool for this to happen.[77][78] As a response to the safety concerns, a heating element on the lens was developed.[79][80]
Programmable visibility signals
Signals such as the 3M High Visibility Signal and McCain Programmable Visibility signal utilize light-diffusing optics and a Fresnel lens to create the signal indication. The light from a 150 W PAR46 sealed-beam lamp in these "programmable visibility" signals passes through a set of two glass lenses at the back of the signal. The first lens, a frosted glass diffusing lens, diffuses the light into a uniform ball of light around five inches in diameter. The light then passes through a nearly identical lens known as an optical limiter (3M's definition of the lens itself), also known as a "programming lens", also five inches in diameter.[citation needed]
Using a special aluminum foil-based adhesive tape, these signals are "masked" or programmed by the programming lens so that only certain lanes of traffic will view the indication. At the front of these programmable visibility signals is a 12" Fresnel lens, each lens tinted to meet United States Institute of Transportation Engineers (ITE) chromaticity and luminance standards. The Fresnel lens collimates the light output created by the lamp, and creates a uniform display of light for the lane in which it is intended. These signals were first developed by the 3M Company in the late 1960s,[citation needed] and were popular in the late 1970s as traffic density increased.
In addition to being positioned and mounted for desired visibility for their respective traffic, some traffic lights are also aimed, louvered, or shaded to minimize misinterpretation from other lanes. For example, a Fresnel lens on an adjacent through-lane signal may be aimed to prevent left-turning traffic from anticipating its own green arrow.
Today, McCain Traffic Systems is the only U.S.-based manufacturer producing optically programmable traffic signals similar to the 3M model.[citation needed] Intelight Inc. manufactures a programmable traffic signal that uses a software-controlled LED array and electronics to steer the light beam toward the desired approach.[81] The signal is programmed unlike the 3M and McCain models. It requires a connection to a laptop or smartphone with the manufacturer software installed. Connections can be made directly with a direct-serial interface kit, or wirelessly with a radio kit over WIFI to the signal.
In addition to aiming, Fresnel lenses, and louvers, visors and back panels are also useful in areas where sunlight would diminish the contrast and visibility of a signal face.
Typical applications for these signals were skewed intersections, specific multi-lane control, left-turn pocket signals or other areas where complex traffic situations existed.
Conventional lighting systems
Conventional traffic signal lighting, still common in some areas, utilizes a standard light bulb. Typically, a 67, 69, or 115 watt medium-base (household lamp in the US) light bulb provides the illumination.[citation needed] Light then bounces off a mirrored glass or polished aluminium reflector bowl, and out through a polycarbonate plastic or glass signal lens. In some signals, these lenses were cut to include a specific refracting pattern. Crouse-Hinds is one notable company for this practice. In the 1930s throughout the 1950s, they utilized a beaded prismatic lens with a "smiley" pattern embossed into the bottom of each lens.[citation needed]
Light design
In the United States, traffic lights are currently designed with lights approximately 12 inches (300 mm) in diameter. Previously the standard had been 8 inches (200 mm); however, those are slowly being phased out in favor of the larger and more visible 12 inch lights. Variations used have also included a hybrid design, which had one or more 12 inch lights along with one or more lights of 8 inches (200 mm) on the same light. For example, these "12-8-8" (along with 8-8-8) lights are standard in most jurisdictions in Ontario, Manitoba, and British Columbia (that, is, the red light is 12 and others 8, making the red more prominent).[citation needed]
In the United Kingdom, 12 inch lights were implemented only with Mellor Design Signal heads designed by David Mellor. These were designed for symbolic optics to compensate for the light loss caused by the symbol. However, following a study sponsored by the UK Highways Agency and completed by Aston University, Birmingham, UK, an enhanced optical design was introduced in the mid 1990s. Criticism of sunlight washout (cannot see the illuminated signal due to sunlight falling on it), and sun-phantom (signal appearing to be illuminated even when not due to sunlight reflecting from the parabolic mirror at low sun angles), led to the design of a signal that used lenslets to focus light from a traditional incandescent bulb through apertures in a matt black front mask. This cured both problems in an easily manufactured solution. This design proved very successful and was taken into production by a number of traffic signal manufacturers through the engineering designs of Dr Mark Aston, working firstly at the SIRA Ltd in Kent, and latterly as an independent optical designer. The manufacturers took a licence for the generic design from the Highways Agency, with Dr Aston engineering a unique solution for each manufacturer. Producing both bulb and LED versions of the signal aspects, these signals are still the most common type of traffic light on UK roads. With the invention of anti-phantom, highly visible Aston lenses, lights of 8 inches (200 mm) could be designed to give the same output as plain lenses, so a larger surface area was unnecessary. Consequently, lights of 12 inches (300 mm) are no longer approved for use in the UK and all lights installed on new installations have to be 200 mm (8 in) in accordance with TSRGD (Traffic Signs Regulations and General Directions). Exemptions are made for temporary or replacement signals.[citation needed]
Technological advancements
With technologies in developed countries continuing to advance, there is now[when?] an increasing move[by whom?] to develop and implement smart traffic lights on the roads.[where?] These are systems that adapt to information that is received from a central computer about the position, speed and direction of vehicles. They try to communicate with cars to alert drivers of impending light changes and reduce motorists' waiting time considerably.[clarification needed] Trials are currently being conducted for the implementation of these advanced traffic lights but there are still many hurdles to widespread use that need to be addressed; one of which is the fact that few cars yet have the required systems to communicate with these light
Control and coordination
Mounting
There are significant differences from place to place in how traffic lights are mounted or positioned so that they are visible to drivers. Depending upon the location, traffic lights may be mounted on poles situated on street corners, hung from horizontal poles or wires strung over the roadway, or installed within large horizontal gantries that extend out from the corner and over the right-of-way. In the last case, such poles or gantries often have a lit sign[where?] with the name of the cross-street.
- Mounted traffic lights in North America
An example of a wire-mounted traffic light in Fort Worth, Texas.
A typical traffic light on Ninth Avenue in New York City. Note that the traffic light gantry is of a guy-wire masted style, which is unique to New York City.
A vertically mounted traffic light in Boston.
Example of horizontally mounted traffic light in Trenton, New Jersey.
Horizontally mounted traffic lights in Calgary, Alberta.
A bulky tubular metal structure. Not only is the intersection very large, but due to its location on Florida's east coast, the traffic lights must be hurricane resistant.
Angled mast-arms, which were frequently used in the state of Pennsylvania during the 1960s and 1970s.
Three horizontally mounted traffic lights for visibility under a bridge in King of Prussia, Pennsylvania. Pennsylvania typically mounts traffic lights vertically.
In some locations, lights are mounted with their multiple faces arranged horizontally, often with supplemental vertical signals on the side, while others locations use vertical signals almost exclusively. Horizontal signals have consistent orientation, like their vertical counterparts.[82] Often, supplemental curb pedestal mounts, intended to support a signal for a different approach road, are used when primary signals are partially obscured due to structures such as overpasses, approaches around a building that obscure the primary signal mountings, and unusual approach geometry. In Florida, horizontal signals mounted on poles, known as "mast arms", are in wide use due to their lower wind profile, important for minimizing hurricane damage. In areas where wind-load is not as much of a concern as ice-load, such as Illinois or Minnesota, the lights are mounted vertically to reduce the accumulation of ice or snow over the surface of the signal heads. In a few countries such as Japan, South Korea, Mexico and a few jurisdictions in Canada and the US such as Texas, New Mexico, Florida, Wisconsin, Nebraska, Quebec (excluding Greater Montreal), New Brunswick, Prince Edward Island and Alberta, most traffic signals are mounted horizontally.
Traffic signals in most areas of Europe are located at the stop line on same side of the intersection as the approaching traffic (there being both right- and left-hand traffic) and are often mounted overhead as well as on side of the road. At particularly busy junctions for freight, higher lights may be mounted specifically for trucks. The stop line alignment is done to prevent vehicles blocking any crosswalk and allow for better pedestrian traffic flow. There may also be a special area a few meters in advance of the stop line where cyclists may legally wait but not motor vehicles; this advanced stop line is often painted with a different road surface with greater friction and a high colour, both for the benefit of cyclists and for other vehicles. The traffic lights are mounted so that cyclists can still see them.
In Spain, the mounted traffic lights on the far side of the intersection is meant for the traffic that exits the intersection in that particular direction. This is often done due to the pedestrian crossings, so that traffic has to wait if they get a red light. These intersections also come with a stop line in the exit area of the intersection.
In North America, there is often a pole-mounted signal on the same side of the intersection, but additional pole-mounted and overhead signals are usually mounted on the far side of the intersection for better visibility. Most traffic lights are mounted that way in the Western United States and Canada. In Ontario, traffic lights are almost always mounted on the far side of the intersection with poles.
In some areas of the United States, signals facing in up to four directions are hung directly over the intersection on a wire strung diagonally over the intersection (once common in Michigan), or the signal faces traffic in one direction, still hung by wires (but the wire is strung horizontally between two adjacent corners of the intersection). This is common in the Southern and Eastern United States.
In other countries like Australia, New Zealand, Lebanon and the United Kingdom, traffic lights are mounted at the stop line before the intersection and also after the intersection. Some busy intersections have an overhead traffic light for heavy vehicles and vehicles further away.
Efectos
Traffic lights can have both positive and negative effects on traffic safety and traffic flow. The separation of conflicting streams of traffic in time can reduce the chances of right-angle collisions by turning traffic and cross traffic, but they can increase the frequency of rear-end crashes by up to 50%.[83] Since right-angled and turn-against-traffic collisions are more likely to result in injuries, this is often an acceptable trade-off. They can also adversely affect the safety of bicycle and pedestrian traffic.
Traffic lights can increase the traffic capacity at intersections and reduce delay for side road traffic, but can also result in increased delay for main road traffic.[84] Hans Monderman, the innovative Dutch traffic engineer, and pioneer of shared space schemes, was sceptical of their role, and is quoted as having said of them: "We only want traffic lights where they are useful and I haven't found anywhere where they are useful yet."[85]
Between 1979 and 1988, the city of Philadelphia, Pennsylvania, removed signals at 199 intersections that were not warranted. On average, the intersections had 24% fewer crashes after the unwarranted signals were removed.[83] The traffic lights had been erected in the 1960s because of since-resolved protests over traffic. By 1992, over 800 traffic lights had been removed at 426 intersections, and the number of crashes at these intersections dropped by 60%.[86]
Justificación
Criteria have been developed to help ensure that new traffic lights are installed only where they will do more good than harm, and to justify the removal of existing traffic lights where they are not warranted. They are most often placed on arterial roads at intersections with either another arterial road or a collector road, or on an expressway where an interchange is not warranted. In some situations, traffic signals can also be found on collector roads in busy settings.
United States
In the United States, the criteria for installation of a traffic control signal are prescribed by the Manual on Uniform Traffic Control Devices (MUTCD), which defines the criteria in nine warrants:[87]
- Eight-hour vehicular volume. Traffic volume must exceed prescribed minima for eight hours of an average weekday.
- Four-hour vehicular volume. Traffic volume must exceed prescribed minima for four hours of an average weekday.
- Peak hour volume or delay. This is applied only in unusual cases, such as office parks, industrial complexes, and park and ride lots that attract or discharge large numbers of vehicles in a short time, and, for a minimum of one hour of an average weekday. The side road traffic suffers undue delays when entering or crossing the major street.
- Pedestrian volume. If the traffic volume on a major street is so heavy that pedestrians experience excessive delays in attempting to cross it.
- School crossing. If the traffic density at school crossing times exceeds one per minute which is considered to provide too few gaps in the traffic for children to safely cross the street.
- Coordinated signal system. For places where adjacent traffic control signals do not keep traffic grouped together efficiently.
- Crash experience. The volumes in the eight- and four-hour warrants may be reduced if five or more right-angle and cross traffic turn collisions have happened at the intersection in a twelve-month period.
- Roadway network. Installing a traffic control signal at some intersections might be justified to encourage concentration and organization of traffic flow on a roadway network.
- Intersection near a grade crossing. A traffic control signal is often justified at an intersection near a railroad crossing, in order to provide a preemption sequence to allow traffic queued up on the tracks an opportunity to clear the tracks before the train arrives.
An intersection is usually required to meet one or more of these warrants before a signal is installed. However, meeting one or more warrants does not require the installation of a traffic signal, it only suggests that they may be suitable. It could be that a roundabout would work better. There may be other unconsidered conditions that lead traffic engineers to conclude that a signal is undesirable. For example, it may be decided not to install a signal at an intersection if traffic stopped by it will back up and block another, more heavily trafficked intersection. Also, if a signal meets only the peak hour warrant, the advantages during that time may not outweigh the disadvantages during the rest of the day.
Implicaciones legales
In virtually all jurisdictions in which they are used, it is an offence for motorists (and other road users) to disobey traffic control devices, such as traffic lights. Exceptionally, it is not an offence for pedestrians to cross against a red light in the United Kingdom, where pedestrian lights officially give advice, rather than an instruction, although UK pedestrians do commit an offence if they cross a road against the signals of a police officer controlling traffic.
Perhaps the most obvious common traffic-light related offence is failing to stop for a red light. In some jurisdictions, running an amber light may also incur a penalty.[where?][citation needed]
In some jurisdictions (such as Toronto, Washington, D.C., New York City, and California),[citation needed] there are ordinances or by-laws against "gridlocking". A motorist entering an intersection (even if on a green light) but unable to proceed and who gets stranded in the intersection (when traffic ahead fails to proceed), and who remains after the light turns red (thus blocking traffic from other directions) may be cited. The definition of the intersection area is that square where the two streets overlap marked by the inner lines of each crosswalk. (Occupying the space inside the crosswalk lines is itself a traffic infraction, but different from gridlocking.) This gives the meaning to the anti-gridlock slogan "don't block the box". This is sometimes used as a justification for making a turn across the opposing travel lanes on a red light at a busy intersection, by pulling partway into the intersection at a green light waiting to perform the turn, and, if oncoming traffic is not abated before the light changes to red, proceeding to turn once the light has turned red and opposing traffic has stopped. This means that at busy junctions without a protected green arrow for turning traffic, one turns after the light turns red. This maneuver is commonly referred to as "occupying the intersection" or "being legally allowed to complete one's turn". In some jurisdictions, including most American states, a vehicle already in the intersection when the light turns red legally has the right of way, and vehicles who have green must yield to the vehicle in the intersection.
In Sackville, New Brunswick, it is customary for through traffic to voluntarily yield to the first oncoming left-turning vehicle to allow it to perform a "Pittsburgh left" manoeuvre.[citation needed] This is similar to a hook turn performed in Melbourne, Australia, which is legal at signed intersections.
Enforcement of traffic lights is done in one of several ways:
- by police officers observing traffic, and issuing citations to motorists who violate the signal
- as a result of an accident investigation, if it is determined that one or more motorists ran the red light – even if the incident was not observed by a police officer
- with red light cameras
Red light running
Jurisdictions differ somewhat on how to deal with "red light running" — attempts by motorists to race to an intersection while facing an amber light, in an attempt to beat the red. In some locales, as long as the light is amber when the motorist enters the intersection, no offence has been committed; in others, if the light turns red at any time before a motorist clears the intersection, then an offence occurs. In New York City the amber light is very short (only about three seconds) in order to discourage driving through. In Oregon and other places, a stricter standard applies—running an amber light is an offence, unless the motorist is unable to stop safely. This standard has been criticized[citation needed] as ambiguous and difficult to enforce (red light cameras in Oregon are activated only if a motorist enters the intersection on a red). Red light cameras in New South Wales, Australia, are activated only if a motorist enters an intersection 0.3 seconds after the light has turned red.[88]
In Russia, it is illegal to enter an intersection on a yellow signal, except for situations where motorists are unable to safely come to a stop. Most traffic lights on busy intersections have an additional "flashing green" phase right before the amber phase, warning motorists that the signal is about to change.[89] Some traffic signals also feature an additional aspect (positioned directly to the right of the bottommost aspect, or alternatively, in the same aspect as the amber light) with a digital countdown timer, informing approaching motorists how much time there is left before the signal switches to amber.[89]
Source: IIHS[90]
As urban centers become more dense and vehicles and pedestrians come into closer contact with each other, the risk of crashes increases. With the rapid increase of vehicles for hire through smart phone apps and the competition from taxis and livery cabs, the urgency to complete as many rides in as short a period of time as possible has led to drivers pushing the limits on red lights.[citation needed] According to the IIHS Insurance Institute for Highway Safety, every year red light running causes hundreds of deaths, thousands of injuries and hundreds of millions of dollars in related costs.[91]
In Spring 2015, Hunter College in New York City completed an observational study of red light running, the first of its kind. The conclusion, after monitoring 3,259 vehicles at 50 intersections over a period of days around the 5 boroughs, found that almost 10% of vehicles and 15% of taxis ran the red light, amounting to nearly 400,000 red lights run every single day.[92] New York City Mayor Bill de Blasio launched a Vision Zero plan to reduce vehicular and pedestrian fatalities. The New York City Police Department's 2014 TrafficStat report showed 33,577 red light tickets for 2013, which is 126% increase in the number of failure-to-yield summonses and red-light running violations.[93]
The Amber Gambler Twins is one of many public interest films trying to change the public's behavior regarding running of amber lights.[94][95]
A 2017 survey in the USA showed that 92.9% US motorists found unacceptable running a red light, when 42.7% of them did it in the previous 30 days. 91.4% of motorists perceive breaches in the red light systems as a serious or somewhat serious personal safety concern[96] · .[97]
Red light runners involved in multiple-vehicle crashes are more likely male, younger, involved in prior crashes, or have alcohol-impaired driving convictions.[96]
Red light cameras
In some countries, red light cameras are used for either the driver or the vehicle's owner. An automated camera is connected to the triggering mechanism for the corresponding traffic light, which is programmed to photograph a vehicle and driver crossing against the light. Either the driver or the vehicle's owner (depending on the locale) are fined for the violation. In some jurisdictions, including the United States and Italy, private companies have been contracted to operate traffic-related cameras and receive a portion of the resulting revenues. In some cases red light cameras have been abused by local governments, where vehicle operators have been fined as a result of traffic systems that have been improperly modified.[98][99] Despite the fact that cameras can reduce the number of crashes, it has been proven that at these intersections drivers tended to react quicker to an amber light change when stopping.[100][101] The consequence of this change could be the slight decline in the intersection capacity.
Confirmation lights
Another way police officers have begun to combat red light runners is with blue or white Confirmation Lights.[102] These lights can be seen from any angle in an intersection and are typically utilised by emergency responders who actuate traffic signal preemption devices to verify that other motorists are facing a red signal. However, confirmation lights also assist officers – who do not have to have a line-of-sight with a red light – to catch vehicles illegally entering an intersection. They are only lit when the red light on the same signal head is on. Some intersections will also have multiple confirmation lights for a single direction of travel if there are different signals for different directions. These lights are separate from the main ones, often protrude above or below the main traffic light, and are much smaller than a standard light to help avoid confusion.
In the Netherlands, many traffic signals that are red can be seen from the side via a small bulbous window, indicating to drivers (and police officers) whether the signal in the crossing direction is actually red or not, by simply leaking out some of the red light through the side of the traffic signal. This has gradually become less common as traditional incandescent signals are replaced by LED signals, while increasingly red light cameras are used to detect driving-through-red violations.[citation needed]
Light timing length
The length of amber lights can differ, for example in many places the length of an amber light is usually four or five seconds, but elsewhere it may be as little as three, considerably reducing the time for reaction. It is typical for these times to vary according to the set speed limit, with longer times for higher limits. In the U.S. state of Georgia, an amber light must be lit one second for every 10 miles per hour (16 km/h) of posted speed limit. For intersections with red light cameras, one extra second must be added.[citation needed] In Colorado Springs, Colorado, amber lights at numerous intersections have been noted with durations of approximately two seconds. In the United States, there is a recommended federal safety minimum of three seconds for amber lights.[103]
The time from when a red light is displayed and when a cross street is given a green light is usually based on the physical size of the intersection. This intervening period is called the "all-red time". A typical all-red time is two seconds to allow cars to clear the intersection. In a wider intersection, such as a four-lane road or highway intersection, the all-red time may be as much as five seconds, allowing drivers who could not or would not stop at the amber light enough time to clear the intersection without causing a collision. Two exceptions are in New Westminster, British Columbia, Canada, and Winnipeg, Manitoba, Canada, where there is no all-red time. The change is instantaneous, due to the nature of the older relay operated signals. It is also the case in Montreal, Quebec, Canada.
Turn on red
Some jurisdictions allow right turns when a steady red light is shown.
Non-detected vehicles
In some instances, small vehicles such as motorcycles, scooters, and bicycles may not be detected, leaving the traffic light controller unaware of their presence. When this occurs, the small vehicle may fail to receive the right of way when the traffic light controller skips their phase, such as at traffic lights that are programmed to remain green for the main street and to only service minor movements, such as the side street or a main street left turn lane, on an as-needed basis when there is demand.
For example, small vehicles may not be detected by an induction loop sensor, such as one whose sensitivity has been set too high in an attempt to avoid false triggers. While a typical motor vehicle has a sufficient mass of metal such as steel that interacts with the sensor's magnetic field,[104] motorcycles and scooters have much less mass than cars, and bicycles may not even be constructed with metal. This situation most often occurs at the times of day when other traffic is sparse as well as when the small vehicle is coming from a direction that does not have a high volume of traffic.[105]
United States
Traffic lights that do not service traffic due to non-detection may not meet the federal legal definition adopted by most states for a traffic control signal, which is any device "by which traffic is alternately directed to stop and permitted to proceed".[106][107][108] Meeting this definition is required for any citation to be upheld; traffic signals that fail to meet it may be considered "defective" or "inoperative."[109]
Some jurisdictions require operators to "bring the vehicle to a complete stop before entering the intersection and may proceed with caution only when it is safe to do so,"[110] while others may construe any action to force it to cycle as tampering.[111]
Over 20 states[112][113] in the United States have enacted "dead red" laws that give motorcyclists and sometimes bicyclists an affirmative defense to proceed through a red light with caution after stopping when they are not detected by the traffic light controller.[114][115]
- Arkansas 27-52-206
- California 21800 (d)(1)
- Colorado 42-4-612
- Idaho 49-802 (3)(a)
- Illinois 11-306 (c)(3.5)
- Indiana 9-21-3-7 (b)(3)(D)
- Kansas 8-1508 (c)(4)
- Kentucky 189-338 (6)
- Minnesota 169.06 Subd. 9
- Missouri 304.285
- Nevada 484B.307 (8)(d)
- North Carolina 20-158 (e)
- Ohio 4511.132 (A)
- Oklahoma 47-11-202 (3)(d)[116]
- Oregon 811.360 (2)(a)
- Pennsylvania 75-3112 (c)(2)[117]
- South Carolina 56-5-970 (5)
- Tennessee 55-8-110 (b)
- Utah 41.6a.305 (7)
- Virginia 46.2-833 (B)
- Washington 46.61.184
- Wisconsin 346.37 (1)(c)(4)
- Pending Legislation: Massachusetts MA H.3182
- Failed: Alabama HB103
- Failed: Nebraska LB 85
- Failed: Wyoming HB0092
En otros contextos
The symbolism of a traffic light (and the meanings of the three primary colours used in traffic lights) are frequently found in many other contexts. Since they are often used as single spots of colour without the context of vertical position, they are typically not comprehensible to up to one in ten males who are colour blind.[citation needed]
Traffic lights have also been used in computer software, such as the macOS user interface, and in pieces of artwork, particularly the Traffic Light tree in London, UK.
Racing
Automobile racing circuits can also use standard traffic signals to indicate to racing car drivers the status of racing. On an oval track, four sets may be used, two facing a straight-away and two facing the middle of the 180-degree turn between straight-away. Green would indicate racing is under way, while amber would indicate to slow or while following a pace car; red would indicate to stop, probably for emergency reasons.
Scuderia Ferrari, a Formula One racing team, formerly used a traffic light system during their pit stops to signal to their drivers to when to leave the pits.[citation needed] The red light was on when the tires were being changed and fuel was being added, amber was on when the tires were changed, and green was on when all work was completed. The system is (usually) completely automatic. However, the system was withdrawn after the 2008 Singapore Grand Prix, due to the fact that it heavily delayed Felipe Massa during the race, when he was in the lead. Usually, the system was automatic, but heavy traffic in the pit lane forced the team to operate it manually. A mechanic accidentally pressed the green light button when the fuel hose was still attached to the car, causing Massa to drive off, towing the fuel hose along. Additionally, Massa drove into the path of Adrian Sutil, earning him a penalty. He finally stopped at the end of the pit lane, forcing Ferrari's mechanics to sprint down the whole of the pit lane to remove the hose. As a result of this, and the penalty he also incurred, Massa finished 13th. Ferrari decided to use a traditional "lollipop" for the remainder of the 2008 season.
Another type of traffic light that is used in racing is the Christmas Tree, which is used in drag racing. The Christmas Tree has six lights: a blue staging light, three amber lights, a green light and a red light. The blue staging light is divided into two parts: Pre-stage and stage. Sometimes, there are two sets of bulbs on top of each other to represent them. Once a driver is staged at the starting line, then the starter will activate the light to commence racing, which can be done in two ways. If a Pro tree is used, then the three amber lights will flash at the same time. For the Sportsman tree, the amber light will flash from top to bottom. When the green light comes up, the race officially begins but if a driver crosses the line before that happens, then a red light will come up and that will be a foul.[citation needed]
As a rating mechanism
The colours red, amber and green are often used as a simple-to-understand rating system for products and processes. It may be extended by analogy to provide a greater range of intermediate colours, with red and green at the extremes.[118]
Galería
LED traffic light (using cap visors)
Temporary LED traffic lights with sensor in Australia
Temporary traffic light in the United Kingdom
Traffic light in a small intersection in Hagerstown, Maryland (using tunnel visors)
Example of traffic signals mounted on gantries in downtown Cincinnati, Ohio, and integrated with street signage
Typical set of traffic lights in East Lansing, Michigan
Typical example of traffic lights mounted on a wide street in California
One example of traffic lights on a suburban street in Santa Clarita, California
LED traffic lights in Örnsköldsvik, Sweden
Typical set of traffic lights in Spain
The green on top light in Tipperary Hill, Syracuse, New York
LED pedestrian signal in New York City
Traffic light in Ashgabat, Turkmenistan
A Marshalite traffic signal, as formerly installed at various intersections in Melbourne, Australia, indicating how much time remained before a signal change.
East Rembo Buting Intersection Traffic light near Kalayaan Ave.
A U-turn traffic light in Lake Buena Vista, Florida.
En Unicode
In Unicode, the symbol for U+1F6A5 🚥 HORIZONTAL TRAFFIC LIGHT and U+1F6A6 🚦 VERTICAL TRAFFIC LIGHT.
Ver también
- Ampelmännchen
- Glossary of road transport terms
- Induction loop
- Level crossing
- North American railroad signals, rail equivalent
- Pedestrian crossing
- Railway signal, another rail equivalent
- Ramp meter
- Traffic light coalition
- Traffic light control and coordination
- Traffic-light signalling and operation
- Traffic optimization
- Traffic robots in Kinshasa
- Slow Children At Play
- Smart traffic light
- Yellow trap
Notas
- ^ These are typically older signals. There are many examples in Houston, Texas, of this. Suspended lights constructed so that a single source simultaneously illuminates all four directions always have this characteristic: Red (in two directions) and green (in the two cross directions) with Red-amber-Green sequence on two sides and Green-amber-Red sequence on the cross sides[citation needed]
- ^ Not completely correct: a variable speed sign is not solely used for the purpose of slowing the speed of motorists approaching an intersection. They are also used on freeways where the maximum safe speed is dependant on the conditions of the roadway (i.e. weather, falling rocks, risk of wildlife, etc.), such as in British Columbia, Canada.
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[Professor Roni Gamzo would probably be interested to know that the word traffic light is made up of the basics of the words "hint" and "light" - the light hints to cars and pedestrians what they should do. The word was renewed after the placement of the first traffic light in Israel, in the city of Haifa in 1949.]
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Mayor Adriano Alessandrini is now accused of shortening the duration of amber lights to boost the profits of the red light camera program. The move paid off, with 2,425,801.60 euros (US$3,206,078.01) in revenue generated from motorists who did not have adequate time to stop, according to prosecution documents.
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Citas
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enlaces externos
- FHWA Arterial Management Website, latest information on traffic signal operations
- Animations of various US signal phasings
- SCATS – Sydney Coordinated Adaptive Traffic System
- Safety Evaluation of Converting Traffic Signals from Incandescent to Light-emitting Diodes: Summary Report Federal Highway Administration
- Safety Evaluation of Discontinuing Late-night Flash Operations at Signalized Intersections: Summary Report Federal Highway Administration
- Traffic signals, 1922, digitized NYPD photograph from the Lloyd Sealy Library Digital Collections