Traffic light myths busted: Can you get a green run?

If you've ever daydreamed about getting a green light all the way up the street on your way to work, you can dream on.
Opus Wanganui senior engineering officer Warren Crockett says Wanganui's 12 sets of traffic lights are demand-activated, not co-ordinated in sequence, so getting a green light all the way could only be coincidence.
The lights, which cost $140,000 to $150,000 a set, are controlled by wire detectors laid in a double figure-eight in the road. The cut marks in the tarseal are sometimes visible just behind the white line at the lights.
The detectors don't sense the weight of the vehicle, they sense metal mass, which is why cyclists and motorcyclists have problems getting the lights to work.
It's also why driving up slowly and hoping the lights will turn green before you have to stop won't help if the detectors haven't been activated by another vehicle or a pedestrian.
Some of the lights will default back to green if there are no other cars around. For instance, the lights on Anzac Pde at the intersection with the City Bridge will favour traffic turning right on to the bridge.
Mr Crockett said the best chance of bikes setting the detectors off was to ride down the middle of the sensors, in the centre of the lane, and not on the painted lines.
Another option was to press the pedestrian crossing button to force the lights to cycle, he said.
When the green light was activated, it would remain green for five or six seconds, extending a further two seconds for each car that passed over the sensor for a maximum time of 20-30 seconds.
If the gap time or the maximum time was exceeded, the lights would change.
Mr Crockett said the maximum time varied at each intersection, depending on traffic volume on any given approach.
The amber light lasted for four seconds and all the lights would remain red for one second before the sequence continued to ensure the intersection was cleared.
If the lights were only letting one or two cars through before turning amber, they probably had a fault.
If people did notice anything wrong with the signals, they should contact the council.
Each set of lights has its own controller, which is customised to the intersection depending on how many vehicles travel through it, the number of lanes, roads and the pattern of approaches.
The most complicated set of lights in Wanganui is at the intersections of Dublin St/Victoria Ave and St Hill St/Guyton St, which offer drivers a right turn or straight right option depending on cars, and additional options for cycle lanes and pedestrians.
It is usually only New Zealand's biggest cities, or cities with special circumstances, that have timed traffic signals, which helped ease congestion at peak times. It is at these lights that you can get a run of green if you get the timing right.