why do stop lights make you press the walk sign button?

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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

6 Answers

Anonymous 0 Comments

If no-one needs to cross the road, it would be pointless to stop the traffic. By requiring pedestrians to press the button you can keep the traffic interruptions to a minimum and only when there is actually someone who needs to cross.

Anonymous 0 Comments

Think of it like the turn arrow. If there’s no car in the turn lane the sensor will never be tripped and the arrow will never turn green. The button is the simplest way to let the system know someone wants to cross so the walk sign turns on rather than the don’t walk staying illuminated.

Anonymous 0 Comments

The only stop lights I’ve seen with that button, are stop lights in places like highways or with high speed traffic that don’t need a stop light due to a low amount of people needing to cross.

Anonymous 0 Comments

For crossing a wide road, the normal green light may not be long enough for a pedestrian to safely cross, so the pedestrian indicator doesn’t go to walk on a normal cycle. Pushing that button makes the parallel green last longer, and activates the pedestrian indicator.

Anonymous 0 Comments

Normal lights will only activate the pedestrian crossing if a pedestrian presses the button – this saves motorists waiting when there is nobody needing to cross.

In really busy locations, some crossings will include the pedestrian crossing by default without a button – in some busy locations where there are virtually always pedestrians crossing. There will still be a button installed (even if it does nothing) so that all crossings are the same and people don’t get confused if some have buttons, and some don’t.

There are also some modern crossings that change how they function depending on the time of day – at busy periods they will follow one set of timings between cycles, or work automatically, at others the timings may change or the cycle will be based on sensors detecting vehicles and pedestrians pressing the button rather than a strictly timed sequence.

Anonymous 0 Comments

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.