Oops! Was that green light shorter than usual?

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Have you been caught out at an intersection that you regularly travel through because the green light seemed shorter than usual?

RACV regularly get calls from upset members who have been caught by a red light camera at an intersection they are familiar with. Most believe they know how many cars are able to get through the green light, particularly on right turns, and drive accordingly.

Traffic at night

Traffic signals are dynamic

What some motorists don’t understand is that traffic signals run on a sophisticated system, called SCATS. This constantly assesses how many vehicles are travelling through the intersection in each direction. The system then adjusts the length of the green light to compensate. This ensures queuing and delays are minimised.

Many intersections are also linked to adjacent intersections along a major traffic route. The timing of the signals is then governed by creating the best traffic flow along the route.

You may regularly turn right at an intersection and ‘know’ that, for example, approximately six cars will get through on the green. However, at another time of day this will differ. And on a different day of the week this may also change, because traffic conditions have changed.

The system also gives priority to trams and buses at some intersections. While some motorists might not appreciate this, giving these mass-transit modes priority reduces congestion by encouraging people to use public transport. In some locations, pedestrians may also get a longer crossing time where many people cross, or slower pedestrians are present. This may also change the length of green time you receive at the intersection.

Motor vehicles and motorbikes waiting at traffic lights

Drivers’ responsibility

Remember that a huge part of driving is to be aware of what is happening around you. This applies at traffic signals too. You may think you know intersections on your regular routes, but changes in demand alter the signals. You must watch and obey the signals, and be prepared to stop for a yellow light. Don’t lapse into bad habits and put yourself or other road users at risk.

Written by Lindsay Layzell, Senior Engineer
December 13, 2016