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As per with the American Disability Act (ADA), audible pedestrian signals are supposed to be implemented in most traffic signal projects. These audible signals are designed to assist visually impaired individuals in crossing streets.

Though I can understand the use of these signals and how they help visually impaired people in knowing that its safe to cross,what I have never been able to figure out is why do the audible notifications (i.e the beeps or cuckoos) stop after a short while and do not last the entire duration for which an individual can cross the street ?

If I was blind and I used the audio notifications as a cue to start crossing,wont the stopping of these audio notifications (after a short duration of like 5 seconds when you can actually still cross the street for 20 more seconds) cause confusion about whether there is still some time left over to cross the street ?

I am assuming this is a design flaw because if the purpose of the audio cue was to only inform visually impaired users to start walking across,how will they know when time is running out or has run out and its dangerous to cross the street.

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In Sweden this is not the case, maybe you should learn from us? :) –  Benny Skogberg Mar 13 '12 at 8:11
    
Maybe :),but at least in Seattle,all the traffic crossings I have come across have this issue –  Mervin Johnsingh Mar 13 '12 at 8:12
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4 Answers

up vote 8 down vote accepted

This question only has a localized relevance, since around the world different countries, and even states within those countries, can have different behaviour. Thus while Vitaly's answer is likely correct, then a large number of responses to this question will be That's not true where I am.

For example: (If Wikipedia is correct)

Audible signals, such as beeps, in order to help blind or partially-sighted pedestrians; or a short recorded message, as in Scotland, Hong Kong, Singapore and some parts of Canada (moderate to large urban centres), the United States, including Michigan, Massachusetts and Texas. In Japan, various electronic melodies are played, often of traditional melancholic folk songs such as "Tōryanse" or "Sakura". In Croatia and Sweden, beeps (or clicks) with long intervals in-between signifying "don't walk" mode and beeps with very short intervals signifying "walk" mode.

I think Croatia and Sweden have excellent ideas there and probably this is implemented elsewhere in the world too, maybe with slight variations from place to place - each country being at a slightly different stage or opinion of what's the best solution.

Perhaps the traditional songs might also be useful because you can tell how far through the song you are as you arrive, but it's a bit of a fluffy method with which to treat something serious like a pedestrian crossing...

In any case, the audible signal may not be the only method of determining state as in some areas, audible signals are switched off at night (or for some reason cannot be used in a given location) and in these cases tactile signals may be available - for example a small rotating cone on the underside of the button unit when the signal is at green to cross.

As a further indicator of the wide variation in implementation, a study into audible pedestrian signals in the US was made for the US Access Board (Bentzen & Tabor 1998 / Accessible Design for the Blind) and states:

The matrix entitled “Accessible Pedestrian Signals: Product Functional Characteristics” on page 33 [shown below] shows the functional characteristics of each product. Manufacturer information is given on page 34. All products produce a sound, vibration, or both, during the walk interval. Beyond this, there is great variation in the functional characteristics of different products, with some providing information throughout the signal cycle. A few devices have audio output that varies, by message or repeat frequency, as the pedestrian cycle changes from WALK to DON’T START to DON’T WALK

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Great answer. In Australia there's also what they call a "vibrotactile" feedback section on crossing buttons which "pulses" and can be felt by the finger, enabling use by both blind and deaf people. Our crossings also "beep" (at different rates) while the crossing is red and when it turns green. –  Kit Grose Mar 13 '12 at 23:59
    
@KitGrose I think Australia would be only place which will be able to pull off that "vibrotactile" feedback section with its warm weather :) ,cant imagine sticking my hand out in the snow or the rain for that here –  Mervin Johnsingh Mar 15 '12 at 7:31
    
There could be another reason: say you live or work near a traffic intersection; especially in cities, you might only be 5 - 10 meters away from the traffic light itself. If the audio alert is loud, then you're hearing a loud, annoying sound playing for 30 seconds or so, every few minutes, all day long. I am assuming that a long sound is more annoying than a short one; I am guessing that a long sound is more likely to bypass the brain's filter and hit your conciousness, whereas an often heard short sound is easier for your brain to ignore. –  bloopletech Nov 27 '12 at 3:31
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The reason might be just what you said - that the signal is meant to let people know they should start walking. Suppose a signal lasted the entire duration of the green light. Then a blind pedestrian who has just arrived at a crossing, and hears the signal, has no way of knowing whether the signal is going to go on for some time, or whether it's going to stop in a few seconds so that he doesn't actually have enough time to cross. As opposed to the current situation, where he knows for sure that he's got some time left to cross safely.

BTW, here in Israel it does last for as long as you can cross.

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That problem would be easily solved by varying the frequency of the bleeps. And if I am not mistaken, that is how it is done in the Netherlands: the speed of the bleeps increases as time runs out and/or the tone changes. –  Marjan Venema Mar 13 '12 at 9:19
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Yes it would. Which still doesn't mean that that's not the reason behind it :). I don't think it's a design flaw, I'm pretty sure it's intentional, even if it's not the best solution. –  Vitaly Mijiritsky Mar 13 '12 at 10:21
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To answer the question:

Why do Pedestrian Traffic Signals only play the audible crossing notification for only a short duration and not for the entire duration of crossing?

I think the actual answer is 'Nobody has actually done any proper research on it' or at least if research has been done in one country, people in other countries haven't come across it or implemented it.

Presumably the 'safe to cross' indication cuts out early based on an assumption about how long it will take users to finish crossing the road, which could be mathematically modelled.


And as an aside: in the UK even the synchronisation of the signage for sighted people is often done wrong ( too long a delay between the traffic being stopped and the signage indicating that it is safe to cross - so pedestrians learn to just ignore the signage and cross anyway).

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The audio crossing signals I remember hearing are clicks which last throughout the entire duration of the green light, however, they click faster to signal that time is running out.

This way the pedestrian knows when the light is green and if there is enough time to start crossing or not.

Of course, this varies according to location.

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