Traffic Light Introduction Mounting History Pedestrian Scrambles

Traffic lights for normal vehicles or pedestrians always have two main lights, a red one which means stop, and a green one which means go. In most countries there is also a yellow (or amber) light. If the amber light is switched on and unflashing you should stop if you are safely able to do so. In some systems, a flashing amber means that a motorist may go ahead with care if the road is clear, giving way to pedestrians, and to other road vehicles that may have priority. A flashing red essentially means the same as a regular stop sign. There may be additional lights (usually a green arrow or "filter") to authorize turns (called a lead light in the U.S., because it is usually leading the main green light).

Traffic lights for special vehicles (such as buses or trams) might use other systems, such as vertical vs. horizontal bars of white light.

In most countries, the sequence is red (stop), green (go), amber (prepare to stop). In the UK, Germany and Poland, among others, the sequence includes red + amber together before green, which helps draw attention to the impending change to green, to allow drivers to prepare to move off. The single flashing amber signal is used in the UK and Australia at Pelican crossings.

Depending on the jurisdiction, traffic may turn after stopping on a red (right in right-driving countries; left in left-driving countries). In some jurisdictions which generally forbid this, a green arrow sign next to the traffic light indicates that it is allowed at a particular intersection. Conversely, jurisdictions which generally allow this might forbid it at a particular intersection with a "no turn on red" sign. In FranceThe French Republic or France ( French: Republique francaise or France is a country whose metropolitan territory is located in western Europe, and which is further made up of a collection of overseas islands and territories located in other continents. permission to move turn right (or more rarely to turn left or to go straight) on a red light is indicated by a flashing amber arrow (cars do not have to stop but must yield way to other cars and pedestrians).

Traffic light failure in most jurisdictions must be handled by drivers as a four-way stop (or, in Europe, a priority-to-the-right intersection), pending the arrival of a policeFor the band, see The Police. For the Polish town, see Police, Poland. Police forces are government organisations ostensibly charged with the responsibility of maintaining law and order. The word comes from the French, and less directly from the Greek pol officerAny holder of an office or of a post may bear the title officer . Generally, the word officer implies a rank, and degree of decision-making responsibility, higher rather than lower in a chain of command and reporting. However, in some organizations that u to direct traffic. Some jurisdictions (e.g. SwitzerlandThe Swiss Confederation or Switzerland is a landlocked federal state in central Europe, with neighbours Germany, France, Italy, Austria and Liechtenstein. The country has a strong tradition of political and military neutrality, but also of international c or FranceThe French Republic or France ( French: Republique francaise or France is a country whose metropolitan territory is located in western Europe, and which is further made up of a collection of overseas islands and territories located in other continents.), however, have additional rights of way signs mounted above the traffic lights; these kick into effect when the lights are no longer active.

2 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 wires strung over the roadway, or even hung from horizontal poles 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 lighted sign with the name of the cross-street.

Some places mount lights horizontally and others vertically.

CaliforniaCalifornia is a state located in the western United States, bordering the Pacific Ocean. The most populous and third largest state in the U. California is both physically and demographically diverse. The state's official nickname is "The Golden State", wh is particularly fastidious in ensuring that drivers can see the current state of a traffic light. One entrance to a typical large intersection, with three through lanes, two dedicated left-turn lanes, and a crosswalk, may have as many as three traffic lights for the left-turn lanes, three for the through lanes, and a pedestrian signal for the crosswalk. And those numbers must be multipled by four to cover all four ways to enter a typical intersection.

3 History

On December 10December 10 is the 344th day (345th in leap years) of the year in the Gregorian calendar. There are 21 days remaining in the year. Events 1041 Empress Zoe of Byzantium elevates her adoptive son to the throne of the Eastern Roman Empire as Michael V. 1817, 1868Events January 3 Meiji Emperor declares " Meiji Restoration", his own restoration to full power, against the supporters of the Tokugawa Shogunate. January 10 Shogun Tokugawa Yoshinobu declares emperor's declaration "illegal" and attacks Kyoto. Pro-Emperor, the first traffic lights were installed outside the Houses of ParliamentThis may refer to the: British Houses of Parliament. Also known as the Palace of Westminster. Irish Houses of Parliament. in London. They resembled railway signals of the time, with semaphore arms and red and green gas lamps for night use.

The modern electric traffic light is an American invention. As early as 1912, Salt Lake City policeman Lester Wire set up the first red-green electric traffic lights. On August 5, 1914, the American Traffic Signal Company installed a traffic signal system on the corner of 105th Street and Euclid Avenue in Cleveland, Ohio. Based on the design of James Hoge , it had two colors, red and green, and a buzzer to provide a warning for color changes. The first three-color traffic lights were introduced in New York and Detroit in 1920.

The first automatic traffic lights could be seen in Wolverhampton, England in 1927.

For unknown reasons, Garrett Morgan is sometimes mistakenly credited as the inventor of the traffic light. See [1].

4 Pedestrian scrambles

A pedestrian scramble, or Barnes Dance (named for Henry Barnes), is a special traffic light that stops all vehicular traffic. Pedestrians then have exclusive access to the intersection and can cross diagonally across the intersection. Pedestrian scrambles are useful when there is heavy diagonal pedestrian traffic, or heavy pedestrian traffic in general. In intersections with heavy pedestrian traffic, pedestrians have the right of way, blocking drivers from turning. A pedestrian scramble gives vehicles exclusive access to the intersection for a period of time as well.

Hachiko Square , in Shibuya, Tokyo, has a famous pedestrian scramble at an intersection of seven streets (some pedestrian-only) in front of Shibuya Station.

In the United States, the city of Beverly Hills is famous for being the first California city to implement diagonal crossing (at some intersections on Rodeo Drive ).

5 Synchronization

Attempts are often made to synchronize traffic lights so that drivers encounter long strings of green lights. This is only easily done on one-way streets with fairly constant levels of traffic. Two-way streets are often arranged to correspond with rush hours to speed the heavier volume direction. Congestion can often throw off any synchronization, however.

More recently even more sophisticated methods have been employed. Traffic lights are sometimes centrally controlled by monitors, or by computers, to allow them to be coordinated in real time to deal with changing traffic patterns. Video cameras, or sensors buried in the pavement can be used to monitor traffic patterns across a city. Unsynchronized sensors occasionally impede traffic, by detecting a lull and turning red just as cars arrive from the previous light. To prevent this, the most high-end systems use dozens of sensors and cost millions of dollars per intersection, but can very finely control traffic levels. This relieves the need for other measures (like new roads) which are even far more expensive.

In some areas traffic lights may also be turned off late at night when traffic is very light. Under these circumstances, traffic in the main street may get a flashing amber to warn of an intersection. Traffic in the secondary street gets a flashing red (see above), or sometimes the lights are marked as operating at set times only. Some lights outside of fire station s have no green, as they may only turn amber for a few seconds and red for a few minutes a week.

6 Preemption

Some regions have signals that are interruptible, giving priority to special traffic. This is usually reserved for emergency vehicles such as ambulances and police squad car s, though sometimes mass transit vehicles including buses and light rail trains can interrupt lights. There have been some concerns that unauthorized people may have obtained devices that can trigger light preemption. Most of the systems operate with small transmitters that send radio waves or infrared signals that are received by other devices on or near the traffic lights. Sometimes, an additional signal light is placed nearby to warn motorists that an oncoming vehicle is preempting the signals.

7 Unusual traffic-light usages

In parts of Canada (the Maritime Provinces, Ontario and Alberta), a flashing green light has a special meaning. It is similar to the left-turn signal that is attached to a standard green. (Either in the "dogleg" pattern or attached to the bottom of the standard signal. Not the standalone.) In Ontario, this usage is slowly being phased out in favour of the more universally-understood left-turn signal lights.

In British Columbia and in Massachusetts, a flashing green signal is used to warn of a crosswalk at which pedestrians have the ability to stop traffic to allow a safe crossing. In Austria, parts of Mexico, Turkey, and Russia, the green lights will start flashing at the end of the Go or Turn phase to indicate that the amber (Caution phase) lights are about to be engaged. This is useful in fast paced roads to allow for longer slowing down time.

In Kraków (and probably some other parts of Poland) there are signs displaying how fast one has to drive in order to reach the next intersection at the exact time when the light turns green. It is very useful in heavy traffic, but also very uncommon.

In some parts of the United States, traffic lights have been fitted to slowly strobe white lights superimposed on the center of the red light when the red light itself has been illuminated. These seem to be located in situations where the driver may have been travelling for a length time without seeing any traffic lights (such as a controlled-access highway) or in other situations where extra work may be needed to draw attention to the status of the light.

Tianjin in the People's Republic of China has two very special systems of traffic lights, in use since c. 1999/ 2000:

One system is where there is a horizontal bar in a specific colour, with the colour changing and the bar shrinking. The shrinking bar indicates the time remaining in that colour. The colour itself is either red (stop), yellow or green (go). A blinking green one-third-full bar means "reduce speed now", and a blinking yellow full-bar indicates "proceed with caution".

When lights of this system turn from green to red, the diminishing green bar will flash once two-thirds (note: not the full bar) of the green bar is "eaten up", with the remaining third intact. A full, uninterrupted yellow bar will appear for a few seconds before, after a short blink, lights turn red. Immediately after the full red bar appears, a tiny (almost unnoticeable) split/division appears to signify the bit that will not be "eaten up". This corresponds to the usual position of a red light (leftmost, or rightmost if at the other end of the road and at the other side of the pavement; or the upper third). When two-thirds of the red bit is "eaten up", the red light extinguishes, only to be replaced nearly immediately with a full chunk of green (again with the minute division). The process then repeats itself.

Another system is where there is a set of three lights as traffic lights, but every light is an arrow pointing in different directions and every arrow has a colour of its own, to show whether traffic flow is permitted or prohibited in that direction.

The major disadvantage of this system of traffic light is that it is unfamiliar to those who are used to seeing specific colours of the traffic lights at the various ends of a normal traffic light itself (e.g. green rightmost, red leftmost, etc)... It does, however, conserve space.

Elsewhere in China, a blinking green light means "reduce speed now", attempting to stop cars from passing (if that car can still safely stop in time) and is nearly universal in appearance. Some cities or parts of cities show the number of seconds remaining in a specific traffic light colour (a so-called "countdown meter").

Other places where there may be traffic lights (normal or special ones):

at the landing-stage of a ferry and aboard the ferry
at the entrance and exit of a parking place or garage
at the entrance and exit of some car wash es
at a ramp meter
before a drawbridge
before a narrowing of the road
at a fire station

Traffic lights for pedestrians are usually different, see pedestrian crossing. Traffic lights at level railroad crossings are again different. Both of these are to avoid confusion as to whom the signal applies.

8 External links

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Home > Traffic light

1 Introduction