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Comment by w-m | Hacker News Reader

Seems a good place to ask a question I’ve been asking myself for a long time, and couldn’t figure out the answer to: why do lonely crosswalks not immediately turn the lights red for the cars when you push the button? Or at least, after a very short delay (< 3 seconds).

For street crossings with multiple directions and multiple lights, that behavior makes sense. You’re waiting for the next pre-programmed phase that syncs you up with other parts of the crossing. For large roads it might make sense, you don’t want to interrupt the flow of the traffic that is expected to hit a green light down the road at current speed.

But for the lonely crossing light in front of the school building in a small street, why do I have to wait 20 seconds after pushing it, every single time?

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I can't answer your question but I can at least confirm the tech exists!

They do exactly what you're proposing here in the UK (at least, the ones that have been recently upgraded in the town I live do) - if there's no cars around it'll instantly cycle the road lights to red (via amber) and then the pedestrian crossing goes green. Pretty much inside the 3 seconds requested too.

Even the ones with multiple directions. No cars? Ped can go as soon as the road lights are red.

The traffic light system before these upgrades was locked into the same cycle you describe - pressing the button would just add a "pedestrians can go now" phase into the normal light pattern.

Having said all that if there's no cars around I'll just cross the road without interacting with the traffic lights at all lol

I wish my local council would use this. Here on my High Street in South London, my nearest pedestian crossing can take up to two minutes to change, even when there are no cars close. It's frustrating for pedestrians (and motorists, when someone has pressed the button, got fed up, dashed through the moving traffic, and then when the lights do go red there's no-one waiting to cross)

Yeah, the wait can be dangerous too. I grew up in Northern Ireland where the systems are quite simple. For some years I lived in the Netherlands and got used to smart systems that would give me instant green if I could cross etc. But then I returned myself home for a while and was shocked with how often I was waiting, to the point that after a few days I started treating some traffic light systems as optional or to be avoided while crossing elsewhere on the road. The result of the poor system meant I was crossing without any system.

Something I do like about these new lights is that if you do press the button then go out of the crossing area it'll unset the button pressed status (assuming there's nobody else in the crossing areas covered by the light system ofc)

I usually encounter this when a line of cars go through their green and I dash across behind them quick enough for it to unset and not disrupt the normal light cycles. It's a daft little thing but it feels so darn efficient to get across without interrupting traffic, haha

https://www.writetothem.com/

It shouldn't matter whether cars are present or not. Why doesn't it just go red to let the pedestrian cross immediately? Obviously with some min interval to stop abuse.

There's a particularly bad one at a busy foot and cycle path near me. It takes a minute to cross after pressing at all times. I know it's done to ease congestion on the busy road but that's wrong. Congestion should be allowed but only the participants (car users) subjected to it. Otherwise it's just making cars more enjoyable at everyone else's expense.

There is a pedestrian crossing installed in Big Cottonwood Canyon in Utah, by a popular sledding hill, a few miles down-canyon of two large ski hills. It is essentially an "instant" transition crossing. The moment a pedestrian triggers it, it switches on warnings, and very quickly turns to solid red stop. The solid stop lasts upwards of 15 seconds, at which point it turns to a warning stop (stop and roll through, flashing red lights).

There is no cool-down period on how frequently it can trigger, and there is no platooning, so at the end of the day when everyone is going home, intermittent pedestrian traffic, say, one person every 20 seconds, is enough to back traffic up all the way to the end of the canyon.

A simple bit of platooning, or a traffic detector (loops aren't good in the canyons, plows rip em up, so probably a radar based approach), would solve this, for this case at least

I think we DO want to interrupt the flow of traffic. Cars should be slowed down in areas where a lot of people want to cross the street. Want to go fast? Do what they do; ditch the car and walk!

In my hometown there is a light that is nearly instant during low-traffic hours. When I would walk to work in the morning I would press it and it would immediately go yellow->red but when I came home in the afternoon, with higher levels of traffic, I'd have to wait for the cycle.

I've experienced this behaviour. During the middle of the day at an intersection of a side street with a busy street it can take a long time to turn. At night when the busy street isn't so busy, it seems to often turn relatively quickly.

Are you waiting 20 seconds for the cross light to turn amber or 20 seconds for your walk light to come on? Because the latter is always going to take at least ~10 seconds -- the stale green time + the amber time + all-red time.

An intersection I have to use regularly makes pedestrians wait upwards of 120 seconds until they’re allowed to cross.

In Amsterdam, every single intersection I encountered changed in less than 5 seconds, some almost immediately.

This is just a choice we make.

Waiting for amber takes 20 seconds. Also it’s not a timeout of some case from repeated use. Have to wait even if it wasn’t used for several minutes beforehand.

> Waiting for amber takes 20 seconds. Also it’s not a timeout of some case from repeated use. Have to wait even if it wasn’t used for several minutes beforehand.

That's a regional/local choice. In my area, we have a number of signaled crosswalks which never activate unless someone pushes the button. They are absolutely instant.

They're not traffic signals, though, they are a dozen or so strobing yellow lights. It's effectively a red light based on local law, but it's way more noticeable for approaching traffic.

A lonely crossing light may still be synchronized with the intersections ahead and behind.

That doesn't explain why that choice was made.

In general, traffic light synchronization is very important to optimize street capacity, but it depends on heuristics limited by the sensor, modelling, programming etc. resources.

Yes, but you say it like it's an inherent issue rather than a design choice. Dutch systems are very smart with these things.

Yes, you can answer why questions on so many levels, e.g. "Because the designers were not Dutch." ;-)

> But for the lonely crossing light in front of the school building in a small street, why do I have to wait 20 seconds after pushing it, every single time?

You don't have to, just cross the street and ignore the "criminalisation" of said basic action (i.e. crossing an empty street) as "jay-walking".

Some are fast.

In a place I used to live there was an very low traffic intersection on a road between my office and my home where the light was misprogrammed or had a bad trigger and would consistently take many minutes before switching to one direction (the direction between my home and office). But hitting the crosswalk to cross the perpendicular road would make it turn green (and the always-green direction red) in seconds. I believe the button instantly set the light to yellow, so the only delay was the yellow time.

So if my partner was with me she'd always hop out and hit the button. :P

Of course, perhaps discouraging that behavior is a reason they aren't usually fast like that. :)

The simple answer is that a society cars are heavily prioritized and pedestrians and cyclists are not.

So traffic engineers by default set crossing buttons to have a delay so the poor motorists aren't somehow inconvenienced by a person wanting to cross.

Note that I'm not referring to lights where pushing the button inserts a crosswalk cycle into the next light change. I'm talking about single street crossings where you push the button and nothing happens for anywhere from 30 seconds to minutes.

Do you not have zebra crossings where you are? Striped line going across the road, with "flashing amber beacons" on either side, where cars must stop if someone is crossing or waiting to cross.

I think they're mainly a UK/Ireland thing, which confused the hell out of me when I went to continental europe and saw the same road markings paired with actual traffic lights + button. (here, that'd be a "pelican crossing" and have different road markings)

Yes, we do have those in the US.

The versions that I hate are where there are always flashing yellow lights at those whether there is a pedestrian present or not. It is confusing and teaches people to ignore the flashing light as it is meaningless. I prefer the kind where a pedestrian presses a button and the lights flash to tell the cars to stop.

Around here the lights either turn green shortly after you press the button (with a minimum wait time between greens), or there are no buttons at all (or they exist but are ignored).

I can say it's very interesting to see what people from several places consider common on this thread. Most traffic laws seem to be absolutely insane; I wonder insanity there are on my local laws that I'm too used to notice.

I have been wondering the same thing myself. I would go a step further and suggest that non-lonely crosswalks should work to prioritize pedestrians over cars.

Even in a place like California where pedestrians supposedly have the right-of-way, it would encourage more walking if we try not to make it an inconvenience.

> why do lonely crosswalks not immediately turn the lights red for the cars when you push the button? Or at least, after a very short delay (< 3 seconds).

The ones in my part of the US do this when the traffic is light or nonexistent, but only with the streets that have car sensors embedded in them.

> ... why do lonely crosswalks not immediately turn the lights red for the cars when you push the button?

Sometimes Occam's razor[0] provides a satisfactory explanation:

Traffic engineers have to take into account people pressing a request button at an arbitrary point in time, or with high frequency, which can cause significant negative impact to traffic flow if a minimum is not enforced.

While a person, or relatively small set of people, seeking to cross a street is made to wait, the numerous people driving are kept moving such that traffic back pressure can be minimized.

0 - https://en.wikipedia.org/wiki/Occam%27s_razor

Who said anything about frequency? For that explanation to make sense, the designer has to deliberately forget that you can put the delay after the cycle.

> Who said anything about frequency?

I did, for the purpose of presenting a context to try to explore the original question:

>> Seems a good place to ask a question I’ve been asking myself for a long time, and couldn’t figure out the answer to: why do lonely crosswalks not immediately turn the lights red for the cars when you push the button? Or at least, after a very short delay (< 3 seconds).

Just because a pedestrian desires to reach their destination by crossing a road does not negate the desires of those driving to reach their destinations. Neither desire is more important than the other and a legitimate case can be made for slightly prioritizing drivers due to the volume of people involved.

> ... the designer has to deliberately forget that you can put the delay after the cycle.

That choice would prioritize one person, or at most a few, over those in vehicles having the same desire. Plus, it does not factor in impact with regard to other traffic control devices (a.k.a. "stop lights").

I guess the fundamental question is; does the want of one person outweigh those of others if that "one person" happens to be you?

> That choice would prioritize one person, or at most a few, over those in vehicles having the same desire.

I disagree.

The flow of cars is (roughly) continuous, and the button presses are (roughly) randomly timed. Adding a delay to the button does not affect the experience of the cars. They still see a randomly timed red light. Even if there was an hour-long delay (with multiple pushes in flight), that wouldn't prioritize cars in any meaningful way. They'd still see the light change every 2-10 minutes or whatever it is, and whether they are caught by the light will still be random.

So it might as well change right away.

They could have a minimum interval between changes, while still allowing it to change quickly if enough time has elapsed since the previous "walk" signal.

> They could have a minimum interval between changes, while still allowing it to change quickly if enough time has elapsed since the previous "walk" signal.

This approach would not satisfy the very real use-case scenario of pedestrians pressing the request button whilst having no intention to cross.

By having a "request -> delay -> satisfy" workflow, instead of a "request -> satisfy -> delay" one, traffic engineers can at least minimize the impact of random jerks.

Because the button doesn't actually do anything.

Some crosswalks are configured to respect the button press, but in my experience the vast majority don't have any effect whatsoever.

Of course it does something in this instance. Otherwise the light would never change to the barely-used crossing.

There’s a pervasive myth about elevator buttons and crosswalk buttons being there as placebos. Yes, I’m certain there are instances where—when the traffic lights regularly cycle all day long—they might be placebo buttons, but the vast majority of them will at least lengthen the cycle time for your direction, and if appropriate will trigger a change sooner than it would have occurred otherwise.

The close door button in the elevator in my office does nothing, nor does the crosswalk button on the major intersection in front of the office.

I've timed it. It does nothing.

The elevator button thing is not a myth, it's actually quite common. As is crosswalk buttons that do nothing.

The door close button: Yeah, you're right. I was thinking of the lobby call buttons. Ignore that I said anything about that. (Of course the button is still wired up, it just only works in fire service mode in those cases)

As far as crosswalks go: Yeah, on major intersections where light cycling is guaranteed to happen all day, the button may not accelerate the change. But that doesn't apply to "lonely crosswalks", and I bet that same button will work in the middle of the night if the cross-street happens to die off during those hours. I caveated that in my comment.

Your experience might be in dense cities only.

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