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I've been to Heidelberg, Germany recently and I've found things like this in most traffic lights in the city:

enter image description here

If I press it a message that says "bitte warten" (please wait) appears. This is not common where I come from so I don't know if pressing has any additional effect.

Does pressing reduce the waiting time? Or does it just display the message?

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And there were always other people around so that you could not try what happens if the button is not pressed? I would have thought that doing an experiment would be a natural thing for a physicist to do ;) – Carsten S Mar 6 at 11:35
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@CarstenS I did! And the light turns green anyway, but I don't know if it takes longer if I don't press the button than if I press it. – A. A. Mar 6 at 11:55
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Where in the world do such buttons not exist, and then how do pedestrians inform that they would like to cross? – gerrit Mar 7 at 9:21
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You're supposed to hold the button to connect with traffic lights control center and then say "This is insert_your_name, requesting green for pedestrians at intersection of X with Y." loudly and clearly. Control center guys are very busy and they rarely talk back to you. At least, this is what we say to people asking about those buttons here where I live ; ) – Agent_L Mar 7 at 13:32
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@gerrit seems like you need to come out of your bubble and discover the world – Mehdi Mar 7 at 14:01

There are three similar cases.

  • There are traffic lights where the pedestrians usually have a red light and only get a green light if they request it by pushing a button. This seems to be the case in your question. A pedestrian is required to push the button and wait. (A slight variant has induction loops to detect bicycles, but pedestrians are still required to push.)
  • There are traffic lights which are switched off until a pedestrian pushes a button. A pedestrian is not required to push, in that case the normal rules for an intersection/road without traffic lights apply. (Once somebody touches the button and there is a red light, you have to wait ...)
  • There are audible signals for visually impaired pedestrians which can be activated by a similar-looking box.

There have been examples of the first case where the button has no effect and the green light comes according to schedule anyway. Either this has been done as a placebo to keep pedestrians from crossing at a red light, or the traffic lights of the intersection are not configured as originally inteded and the button wasn't removed.

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There are also blue ones with wheelchair / crutches signs on them that will increase the time of the green period when pressed. And either the yellow or the blue ones may have a vibrating metal plate mounted on the top to give tactile feedback to visually impaired pedestrians when the light turns green. – Jörg W Mittag Mar 6 at 11:20
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Also worth noting: contrary to what you may have observed from the behavior of the local natives, pressing the button multiple times in quick succession, pressing it a very long time, pressing it very hard, hitting / kicking it, or yelling at it will not decrease the waiting time :-D – Jörg W Mittag Mar 6 at 11:22
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A third possibility is that at some times of the day the light stays red until the button is pressed, and at other times of they day the whole intersection works to a fixed schedule and ignores the button. – Henning Makholm Mar 6 at 11:38
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There's also the possibility that this is a crossing on a major road, and there is a junction with a minor road. The lights will go to red on the major road and green on the minor road and pedestrian crossing when either a vehicle is waiting at the minor road or a pedestrian pushes the button. – Dezza Mar 6 at 12:48
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"or the traffic lights of the intersection are not configured as originally inteded and the button wasn't removed" - some traffic lights are configured differently depending on the time of the day or the day of the week. As such, the button may well sometimes have an effect. Also, in general, I am not convinced there isn't a fourth case, where traffic lights are generally running on a schedule, but pressing the button decreases the waiting time until the next pedestrians' phase (useful at intersections that sometimes, but not permanently, see lots of pedestrians). – O. R. Mapper Mar 6 at 13:38

Also note that sometimes the main traffic lights directing vehicles operate on their own schedule, and are not effected by the button, but the button controls the operation of the pedestrian walk/don't walk light.

So for example, when there is a separate light for traffic turning left off the main road, across the pedestrian crosswalk, the walk/don't walk light will normally be red, but will turn green only if both the button has been pressed and the left-turn light is not active; ie. it is letting pedestrians to know whether it is safe to cross so they don't have to figure out what is going on with the vehicle traffic lights in a complicated intersection.

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"so they don't have to figure out what is going on with the vehicle traffic lights in a complicated intersection" - or even on a simple one: Traffic lights in Germany are typically on the near side of the junction for each direction (i.e. not across the junction), so normally, one cannot see any traffic lights other than the ones for one's own direction. – O. R. Mapper Mar 6 at 22:47

Im from Germany and i know that it has many reasons and functions:

  • It can be to make the wait between green and red smaller
  • At some cities it is just a sort of placebo (very often)
  • At some intersection you must press it or the light never becomes green (very rare)
  • The most of it have at the bottom a hole with a metal stick
    • This is for deaf people, because the stick vibrates at green phase
    • If you press this stick with SOS morse code it becomes instantly green (very very very rare)
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I don't understand why a deaf person would require any vibration to notify them when the light is green... they can still see the light (and I wouldn't imagine a blind person would want to try to cross a busy street this way!) – Michael Mar 8 at 2:48
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The button at the bottom actually turns the audible signal on. At night the audible signal is automatically turned off so residents can sleep undisturbed, so when someone needs the audible signal to cross he can turn it back on temporarily with that button. The "emergency instant green button" is an urban myth. – Gerald Schneider Mar 8 at 9:55
    
At those lights with blind person support, some people actually mimic the "green!" sound with their mouth when they see a blind person waiting. <click> <click> <click> <RIP> – TheBlastOne Mar 8 at 11:29
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Stop damaging public property by trying out Morse code on buttons! – Dmitry Grigoryev Mar 8 at 11:35

The ones in Heidelberg are required to get a green light as a pedestrian. If you don't press them, it never turns green, it is green for the cars all the time.

You said in comments that it turns green anyway, but somebody else must have pressed either the light on your side or on the opposite side.

For lights in other cities, other rules may apply, as discussed in other answers.

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Might it also depend on the time of day/week and the location of the crossing? In the US, a lot of lights will just assume there's pedestrians during business hours but then go into needs-to-be-pushed mode at night, and it can be hit-or-miss throughout the city. Some crosswalks also only activate blind accessibility noises if the button is pushed. – fluffy Mar 7 at 6:22
    
@fluffy in Heidelberg, it does not depend on business/nonbusiness hours, the buttons need to be pushed all the time. Also, the blind accessibility noise buttons in Heidelberg look differently, they have hand sensors (no mechanical push plate), the "blind" sign (circle with three dots inside) and do not activate a "please wait" light. – rumtscho Mar 7 at 8:36
    
Interesting. Do you have official references for this? And maybe even an explanation as to why this policy was chosen. – JoErNanO Mar 7 at 16:03
    
@joernano I have neither references nor explanations. I have been living in Heidelberg for several years now, and I'm reporting what I experience every day. I must have used a button exactly like the depicted one 5-6 times today alone. – rumtscho Mar 7 at 16:05

In my city in Spain, those buttons reduce 1/3 the time of waiting during day schedule, and, during the night, the pedestrian lights won't ever turn green unless they are pressed.

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In Terrassa, when you press the button, you get a countdown from the time you need to wait until you get a green light. It's supposed to encourage pedestrians to not cross in red -- the reality is that when you see a 70 and no incoming traffic you break the law :p – orique Mar 7 at 18:33

Depends on the traffic light system in use in the particular city or at the particular traffic light.

Some, particularly in less busy areas (usually crossing a single street) keep the vehicle lights green unless someone pushes the button. Some (intersections) skip the pedestrian light cycle and keep them red if no button is pressed.

Certain intersections, particularly busy ones, stick to their cycle and have no button or sometimes even buttons with no effect (other than a little LED), just to give you the idea of having done something :)

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