Saturday, 9 November 2019

Traffic Signal Pie: Automatic For The People

This post is part of an occasional series on traffic signals. This time, I'm discussing push buttons at crossings.

We all know about push buttons at crossings (stand alone or at junctions). They are there to register a demand from people who wish to cross the road;

They are the familiar boxes with the yellow shells (see a toucan crossing above) either attached to the traffic signal post or as a separate post. You also see them as slightly smaller boxes where a second push button is provided such as this chilly example;

There are various push button layouts for various situations;

There are two things to accept when we talk about people having to push a button to register their demand to proceed;
  • Traffic signals are there to manage motorised traffic.
  • The ultimate decision on highway space is political.
So, we end up with the simple act of wanting to cross the road being bumped down the pecking order by both traffic and politics. because we've seen the car as freedom and the politics supported this leaving it harder to cross the road in some places.

Detection for general traffic is pretty much universal using sensors in the road and on the traffic signals. It can be very clever counting vehicles through junctions and the control computers can adapt on the fly. Cycle traffic gets a bit of this where dedicated space is provided, although push buttons are still common.

People on foot (and I include those using wheeled mobility aids) get the raw deal because they have to press a button. Because of the way we configure space and that push buttons are mainly on poles near the kerb, we often make it hard or impossible for some people to press the button. In this film, Esther shows us that poor positioning of push buttons at this crossing makes it impossible for her to reach the button when using her wheelchair;

The problem here is the layout of the island with the push button on a post behind a kerb, so she cannot get close enough to press and so this could potentially be solved with some works, but is does show how easy it is to install something which is useless for many people.

It's also a problem for users of non-standard cycles where the push button cannot be reached without sticking the front of the cycle into the road or for hand cyclists and recumbent users, they are also seated lower down;

The above photo is a little bit of fun, but from my seated position, there is no way I could reach the button and unlike me, there are people who cannot easily dismount or dismount at all.

At multi-stage crossings where there is only one direction people are going to leave the central island (like where Esther was crossing), I think that the signal push buttons should be linked. There is no technical reason why pushing a button cannot register demand at the right time from the island.

Elsewhere, we have to think about how we can avoid people having to push a button at all. It would be possibly to run signals on a timer so the green man (and/ or bike) comes in every so often, but people should be able to turn up and cross and like drivers, we need detection.

I have never seen one myself, but pressure mats have been used in the UK to register someone waiting to cross - there is a report from the early 1990s on the testing of puffin crossings, although this was more about detecting that someone had walked off so the demand could be cancelled. The problem with this technology is that having stuff recessed into the ground puts it at risk from water and failure.

Modern crossings now use clever detection to sense people standing at a crossing using infrared or video with artificial intelligence tracking people through a space. There are companies looking at technology and in London, a pedestrian version of SCOOT is being tested which can extend green times where there are more people wanting to cross.

In time, we should see detection taking over from the need to push a button. I don't know if we'll see the end of the push button completely, but it would be nice to see new displays appearing which can reassure people that they have been "seen" and even better, how long they have until they get to cross (like many other countries manage). Eventually, we need more places were we get rid of traffic to the point where we need far fewer traffic signals, but that's another story!

This post is part of an occasional series on traffic signals - for more posts, search "Traffic Signal Pie" in the search bar or click here.


  1. We'll need to locate the video of Princes Street Edinburgh, where poor management of the surges of Nasser pedestrians, created by not planning the number & sequencing of crossing 'green men' and the footway capacity.

    As the opposing flows 'crashed' head on half way across, or mid-way between crossings and spilled over onto the carriagway. This was a Key factor in the then high level of pedestrian-vehicle collisions.

  2. My biggest bugbear is the punishment wait when you push the button. If the button has not been pushed in the last few minutes then it should turn green immediately. Otherwise all that happens is you wait minutes and rather than delay the current traffic you delay the traffic in a couple of minutes time.

    1. For standalone crossings this really shouldn't be the norm - press and go should be the norm!