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Traffic Signals

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Traffic Signals
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Push Button Unit

Traffic signals direct the flow of traffic, normally at road junctions, pedestrian crossings, and railway level crossings. Their chief purpose is to minimise congestion and improve road safety, and they have a key advantage over other traffic-engineering solutions, such as grade separation, in being comparatively cheap to install and requiring little additional landtake. Traffic signals have been commonplace in the UK and Ireland since the first modern-style automatic system was introduced in Princes Square, Wolverhampton, in November 1927.

Display sequence

A set of vintage SGE signals on Euston Road, London, in the 1960s


In the United Kingdom – as well as in Austria, Belarus, Bosnia and Herzegovina, Bulgaria, Croatia, the Crown Dependencies and Gibraltar, the Czech Republic, Denmark, Estonia, Finland, Germany, Hungary, Iceland, Latvia, Liechtenstein, Lithuania, Malta, Moldova, Montenegro, North Macedonia, Norway, Poland, Russia, Serbia, Slovakia, Slovenia, Sweden, Switzerland, and Ukraine – a standard four-phase signal sequence is used consisting of the consecutive display of green (proceed), amber (stop, unless it is not safe to do so), red (stop), and red-and-amber lights (stop, but prepare to proceed). In other European countries the red-and-amber phase is omitted, the lights changing straight from red back to green.

The standard sequence became so well known following its introduction that by the end of the 1920s, when light-controlled pedestrian crossings were being installed in Manchester, the phases were not documented as it was assumed the public would understand them. The Metropolitan Police, in endorsing the design, pointed out that the simple colour-light scheme could be understood without any knowledge of English, and would therefore be of benefit to foreign drivers.

Push Button Unit (PBU)

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An old PBU, of a type commonly found in the UK
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The 'Push Button Unit' sits on the signal pole or an auxiliary pole and has the purpose of controlling a pedestrian phase on the signals. Many fully automated crossings omit these (e.g. where a pedestrian phase is timed in with existing traffic phases).

Portable Traffic Signals

Portable variants of traffic signals may be used where temporary traffic management measures are required, such as where roadworks are occurring.

Main Article: Portable Traffic Signals (PTS)


Modern traffic signals evolved from the coloured-light indications which accompanied railway semaphore signalling, introduced in the 19th century. Red was used to indicate "stop" as it was already widely known to represent danger.

Traffic signals were regarded as something of a necessary evil during the early to mid 20th century, but by the 1960s, the need to install more signals at pedestrian crossings was becoming more urgent. The first attempt at this was the Panda Crossing, introduced by then transport minister Ernest Marples in 1962, but this suffered criticism for being over-complicated and confusing to users. Consequently, a new design, the now familiar Pelican Crossing, appeared in 1969.

Toucan Crossings followed in the 1990s, for pedestrians and cyclists, so called because "two can cross".

In the 2000s, a new type of pedestrian controlled signal, the Puffin Crossing started to be installed in favour of Pelican Crossings. The principal difference between the two is that the control and the signal is on the same unit facing the user. Also includes on-crossing detectors to reduce unnecessary delays.

In May 2015, Queens Circus Roundabout in Battersea was reconfigured to include a fully signalised cycle route with special cycle aspect signal heads mounted at cyclists eye level. These heads have subsequently been rolled out on some of London's cycle superhighways, where examples can be seen on Farringdon Street.


Main Article: Traffic Signals - Signal Heads

SGE were one of the most significant manufacturers of traffic signals from the 1930s onwards. Their design could generally be identified by the text "STOP" on the red signal, and completely separate housing for each lamp. Another major manufacturer at the time was ATE/ATM, who also began installing signals in the 1930s.

Traffic signals took on a more modern appearance with the introduction of the Mellor head from 1970, and this rapidly replaced the SGE design, including a complete retrofit on pelican crossings in 1973. A key advantage of the Mellor design was that it allowed easy installation of fixed-phase timing, whereas previous installations tended to be vehicle activated. Mellor heads were commonplace until the 2000s, when newer signal heads with modular designs started to replace them.


Traffic Signals
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