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>In some Australian cities, in the central business district, the traffic light push buttons don't work at certain times — for example, 7 am to 7 pm, Monday to

>In some Australian cities, in the central business district, the traffic light push buttons don't work at certain times — for example, 7 am to 7 pm, Monday to Wednesday, and 7 am to 9 pm, Thursday to Saturday. >The rationale is that between these busy hours, the road traffic is relatively constant, and also, the pedestrian crossings are in continuous use. That strikes me as a bit stupid. The slight increase in capacity is really only needed at peak times. They could just do away with the buttons entirely.

phire 10y ago
The traffic lights are optimised for throughput during peak times and optimised for travel time during non-peak times. Throughput optimisation has the lights cycling at a constant rate, 60 seconds in one direction, 60 seconds in the next direction and so on. It's easy to tack the pedestrian cycle on to that (pedestrians walk in parallel with the traffic, though I've also seen lights which give the pedestrians their own cycle, and pedestrians can also walk diagonally across the intersection). The cycle might also be synchronized with other lights. The Travel time optimisation for off-peak is completely different. Lights are always stuck onto a single direction (the direction with the most traffic). When a car triggers the sensor in the perpendicular direction, the traffic light quickly cycles and gives them a green light within 10 seconds. The green light only lasts about 5 seconds, barely enough time for a second car to get through the light. It's impossible to get a third though. But in typical night time traffic, this mode makes the traffic light only slightly slower than a stop sign. Even if a pedestrian did arrive at the traffic light at the same time as a car, there is nowhere near enough time for the pedestrian to get across the road. You can't even run across the road in the allocated time. The button is needed for two reasons. 1) to signal that a pedestrian is waiting. 2) to request the longer cycle that has enough time for a pedestrian to walk across the road.
- userbinator 10y ago
  Lights are always stuck onto a single direction (the direction with the most traffic). When a car triggers the sensor in the perpendicular direction, the traffic light quickly cycles and gives them a green light within 10 seconds. The green light only lasts about 5 seconds, barely enough time for a second car to get through the light. It's impossible to get a third though. Wouldn't it be better for the light to stay at the last direction a car traveled through? In my experience, traffic tends to be quite "bursty" (although that could be because of upstream lights causing that) so it seems a slightly different strategy could work better: as long as there are no cars in the other direction, the light stays green. If there are, the light will change immediately if the current direction has no cars; otherwise a timer is started and forces the direction to change when it expires. This seems to incorporate both optimisations you describe.
  - phire 10y ago
    I live on a residential street with this style of traffic light along it. I suspect the cycles have been designed this way to also minimise the amount of noise. One or two cars every 30 seconds is less distracting than 5 cars in a row followed by 3min of silence.
dingle_thunk 10y ago
Australian traffic signals are also 'smart'. They don't cycle in non-peak hours. They just use sensors to detect oncoming traffic and route appropriately. Main roads default to green, but lights on side roads will switch just before you drive up to them. This is why the buttons are necessary during non-peak hours... If I press the button, the light will go red as soon as it's safe. Jaywalking isn't a crime here, but this is still very useful in some situations. Our "Coordinated Adaptive Traffic Control" systems are pretty awesome. Even during peak traffic, all the lights are controlled by a central control room, with a computer that manages all traffic flow as efficiently as possible. It will sometimes shut down a lane or modify a speed limit to allow emergency traffic through or prevent grid-lock further down the freeway, reducing overall travel time. It's able to simulate different traffic flow models and select the best one. The result is that even during peak hours, I can easily travel from the outer suburbs to the CBD (30k/20mi) in approx 40 minutes. Details here: http://www.scats.com.au/ http://www.scats.com.au/

phire 10y ago

The traffic lights are optimised for throughput during peak times and optimised for travel time during non-peak times. Throughput optimisation has the lights cycling at a constant rate, 60 seconds in one direction, 60 seconds in the next direction and so on. It's easy to tack the pedestrian cycle on to that (pedestrians walk in parallel with the traffic, though I've also seen lights which give the pedestrians their own cycle, and pedestrians can also walk diagonally across the intersection). The cycle might also be synchronized with other lights. The Travel time optimisation for off-peak is completely different. Lights are always stuck onto a single direction (the direction with the most traffic). When a car triggers the sensor in the perpendicular direction, the traffic light quickly cycles and gives them a green light within 10 seconds. The green light only lasts about 5 seconds, barely enough time for a second car to get through the light. It's impossible to get a third though. But in typical night time traffic, this mode makes the traffic light only slightly slower than a stop sign. Even if a pedestrian did arrive at the traffic light at the same time as a car, there is nowhere near enough time for the pedestrian to get across the road. You can't even run across the road in the allocated time. The button is needed for two reasons. 1) to signal that a pedestrian is waiting. 2) to request the longer cycle that has enough time for a pedestrian to walk across the road.

userbinator 10y ago
Lights are always stuck onto a single direction (the direction with the most traffic). When a car triggers the sensor in the perpendicular direction, the traffic light quickly cycles and gives them a green light within 10 seconds. The green light only lasts about 5 seconds, barely enough time for a second car to get through the light. It's impossible to get a third though. Wouldn't it be better for the light to stay at the last direction a car traveled through? In my experience, traffic tends to be quite "bursty" (although that could be because of upstream lights causing that) so it seems a slightly different strategy could work better: as long as there are no cars in the other direction, the light stays green. If there are, the light will change immediately if the current direction has no cars; otherwise a timer is started and forces the direction to change when it expires. This seems to incorporate both optimisations you describe.
- phire 10y ago
  I live on a residential street with this style of traffic light along it. I suspect the cycles have been designed this way to also minimise the amount of noise. One or two cars every 30 seconds is less distracting than 5 cars in a row followed by 3min of silence.

dingle_thunk 10y ago

Australian traffic signals are also 'smart'. They don't cycle in non-peak hours. They just use sensors to detect oncoming traffic and route appropriately. Main roads default to green, but lights on side roads will switch just before you drive up to them. This is why the buttons are necessary during non-peak hours... If I press the button, the light will go red as soon as it's safe. Jaywalking isn't a crime here, but this is still very useful in some situations. Our "Coordinated Adaptive Traffic Control" systems are pretty awesome. Even during peak traffic, all the lights are controlled by a central control room, with a computer that manages all traffic flow as efficiently as possible. It will sometimes shut down a lane or modify a speed limit to allow emergency traffic through or prevent grid-lock further down the freeway, reducing overall travel time. It's able to simulate different traffic flow models and select the best one. The result is that even during peak hours, I can easily travel from the outer suburbs to the CBD (30k/20mi) in approx 40 minutes. Details here: http://www.scats.com.au/ http://www.scats.com.au/