This isn’t all stop lights. At many lights the button doesn’t do anything. But at some of them you do have to press the button. What is the purpose of making you press the button?
In: Engineering
A huge part in making an intersection function well is that you have to make it aware of traffic flow. And traffic *volume*.
The controller knows, at the very least, which lanes got actual cars in them that are waiting.
Often it also knows how many cars are in each lane, if there is traffic oncoming that risk filling up the intersection. It spots trucks and other heavy vehicles and avoids flipping to red right in front of them (because that’s kind of dumb, since it may not be possible for them to hit the brakes fast enough anyway) and is sometimes able to spot emergency vehicles with their flashing lights turned on to help them get through.
Since this makes room for a lot of adaption, it only flips to green *for as long as it’s needed*.
It doesn’t really make sense that the lights flip to green for a minute every three minutes to let on cars when there are just 50 cars in total trying to get out on a normal day; instead it just flips the light long enough to let a car out. And only when there actually is a car to let out.
This behaviour doesn’t work that well with pedestrians. Because pedestrians assume that they always get the same set of time to get across. And, well. They do get the same set of time. Because pedestrians can be elderly people. Vision impaired. And so on. And you don’t want to strand them in the middle of the road unnecessarily. That is what the button is for. The button tells the controller to fire up an inactive scheme temporarily. A scheme that is designed to give a pedestrian a predetermined set of time to pass. And while it does that, it takes it’s chances and flips a few other lights to green too and let some cars through that are not bothering the pedestrian much. Once the timer is out, it goes back to the standard program where it adapts to traffic again.
EDIT: I forgot to add that if the button is not working, it’s probably because the programed times are already always long enough to let a pedestrian over. And the light flips green *in parallel* with other traffic. It’s a pretty typical workaround if the buttons are broken and no-one bothers to fix them.
If it was made that way, it would have had ticker boxes without buttons. No use buying a button if you are not gonna use it.
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