Traffic light
[3] Traffic lights normally consist of three signals, transmitting meaningful information to road users through colours and symbols, including arrows and bicycles.
Although this is internationally standardised,[4] variations in traffic light sequences and laws exist on national and local scales.
[8] In 1912, the first electric traffic light was developed by Lester Wire, a policeman in Salt Lake City, Utah.
[9] It was installed by the American Traffic Signal Company on the corner of East 105th Street and Euclid Avenue in Cleveland, Ohio, on August 5, 1914.
[16] In 1923, Garrett Morgan patented a design of a manually operated three-way traffic light with moving arms.
The most common signal type has three aspects facing the oncoming traffic: red on top, amber (yellow) below, and green below that.
[citation needed] In a fourth type, sometimes seen at intersections in Ontario and Quebec, Canada, there is no dedicated left-turn lamp per se.
[30][31] The United States is not party to the Vienna Convention; rather, the Manual on Uniform Traffic Control Devices (MUTCD) outlines correct operation in that country.
[33] The MUTCD specifies the following vehicular signals:[32] In the Canadian province of Quebec and the Maritime provinces, lights are often arranged horizontally, but each aspect is a different shape: red is a square (larger than the normal circle) and usually in pairs at either end of the fixture, amber is a diamond, and green is a circle.
In many southern and southwestern U.S. states, most traffic signals are similarly horizontal in order to ease wind resistance during storms and hurricanes.
In the UK, these crossings normally need at least four traffic signals, which are of a regular type (red, amber, and green), two facing in each direction.
In the Australian States of Queensland, New South Wales, Victoria, and Western Australia, the sound is produced in the same unit as the push buttons.
When the light changes, a speaker built into the button will play a recording to notify blind people that it is safe to cross.
MUTCD specifies a standard vertically oriented signal with either two or three lenses, displaying white lines on a black background.
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.
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.Some regions have signals that are interruptible, giving priority to special traffic, usually emergency vehicles such as firefighting apparatus, ambulances, and police cars.
[67] "Phases" (or "signal groups" in Australia and New Zealand) are indications show simultaneously, e.g. multiple green lights which control the same traffic approach.
Detectors come in the form of digital sensors fitted to the signal heads or induction loops within the road surface.
Induction loops are beneficial due to their smaller chance of breakdown, but their simplicity can limit their ability to handle some situations, particularly involving lighter vehicles such as motorcycles or pedal cycles.
[78][79] On the other hand, this turn on red rule is uncommon in Europe, unless an arrow signal or traffic sign specifically permits it.
[citation needed] Moreover, in the event of an individual LED failure, the aspect will still operate albeit with a reduced light output.
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.
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.
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.
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.
[91] Signals can either be placed nearside – between the stop line and the kerbline of the intersecting road – or farside – on the opposite side of the junction.
Nearside signals can be beneficial to road safety, as drivers have more time to see a red light and are less likely to encroach on pedestrian crossings.
"[95] A World Economic Forum study found that signalised junctions are linked to higher rates of localised air pollution.
Drivers accelerate and stop frequently at lights and as such peak particle concentration can be around 29 times higher than during free-flow conditions.
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.
