Blog post

Does Pushing The Button At A Crossing Actually Do Anything?


This Forbes article is from 2017..... It might be due an update!

City life involves a lot of waiting – in queues in the supermarket, on platforms for trains and buses, at red lights in your car or bike, or in lobbies for elevators. But as I see it, time never moves as soul-crushingly slowly as it does when you’re waiting to cross a busy road.

You push the button. You wait. You don’t push it. You wait. You slam the button many times in succession, or give the evil eye to the person who’s standing right by the button, but who chooses not to push it. You watch the traffic pattern (or time the process), so that you can be ready to cross the moment you get a green signal. If you’re anything like me, waiting at crossings can become an obsessively competitive activity.

So, I thought it was time I gave you a definitive answer to the question, ‘Does pushing the button at a crossing actually do anything?’

Unfortunately, I can’t do that, because there is no definitive answer. It seems that if you’re at a standalone pedestrian crossing that is far from any other sort of traffic junction, pushing the button will turn the traffic light red. But at any other sort of traffic-pedestrian interface, what the button does depends on where you are, what time it is, and what type of crossing you’re at.

Now, while I’ve previously written about the complex maths behind traffic flow, I’ve never told you how traffic is managed, and that is particularly important for pedestrians. So, a brief summary: Traffic lights, controlled by computers, take in data from sensors embedded in the road. There are lots of options for detecting vehicles, but the most common sensor is the inductive loop, which makes use of the relationship between electricity and magnetism.

When you pass an electric current through a metal wire loop, you induce a magnetic field around it, and cause it to resonate at a set frequency. If you bring another piece of metal close to the loop (say, a car, for example), its frequency changes. When you remove it (or if the car drives off), the frequency returns to normal. Those changes are easy to detect, and they allow traffic engineers to remotely and constantly monitor traffic flow, counting vehicles that pass by.

Once traffic engineers know how many cars they’re dealing with at a given junction, they can use that to design a light-switching pattern that keeps people moving as much as possible. London uses a system called SCOOT (Split Cycle Offset Optimisation Technique) to continuously optimise this switching routine, and it works 24 hours a day, 365 days a year. Other cities apply different algorithms to manage their traffic, and that choice also has an effect on pedestrians.

In some parts of London, there’s a specific system for those of us who get around on foot. Called Ped-SCOOT, it uses a stereoscopic camera, mounted on the crossing, to count pedestrians. It is activated when a pedestrian bushes the button, and if it detects high numbers of people waiting, it adjusts the traffic light switching time to give you a few extra seconds to cross. Alternatively, if no-one is waiting, or if someone presses the request button and then crosses without waiting, the system detects it and resets the timing to priorities vehicles.

At Oxford Circus – a junction in the heart of London – timing is everything. If no-one presses the button, the lights will skip the requested pedestrian phase, and instead, alternate between giving a green light to each road. But many of the traffic lights on the roads that feed into the junction use timers to manage pedestrians. Generally, pushing those button during the day does nothing at all – the lights will change when they are set to. But at night time, pushing them really does interrupt the light-switching pattern.

In Manchester, only 60% of crossing buttons need to be pressed during peak times, and in Edinburgh, about a fifth of traffic lights are on a timer. According to the BBC, the maximum wait time for a green man in the UK is set at two minutes, but you usually wait for less time than that.

So what about elsewhere? In Australia, it depends what part of the country you’re in. In Sydney, lights in the CBD operate on an automated cycle for most of the day – the rest of the time, you’ve got to push the button if you want to cross. In Melbourne, pushing the button signals that people are waiting to cross, but it won’t make the green appear any faster. In New Zealand’s largest cities, major junctions are entirely automated – it doesn’t matter how many times you press the button, it won’t make any difference. At other junctions, the button works, but only outside of peak traffic hours.

US cities are just as complicated. In Portland, Oregon, the vast majority of buttons really do cause the green man to appear. For many locations in Washington DC, pushing the button activates a ‘chirping’ sound that provides an audio cue of when to cross. But it doesn’t actually change the traffic timing. That’s similar to the situation in San Francisco, where 20% of crossings are ‘pedestrian actuated’, meaning that they directly affect the traffic switching pattern. In Seattle, as in London, it very much depends on the location of the crossing – where adaptive traffic lights have been installed, pedestrians definitely do need to push the button, but in other areas, the switching signal is pre-set. In downtown Boston, the vast majority of pedestrian buttons at busy junctions don’t do anything. Traffic engineers assume there will always be people waiting to cross, so pedestrians get their own cycle every few minutes. But at quieter junctions, pushing the button (even during the day) interrupts the traffic flow.

There’s one more city that’s worth mentioning. A 2004 New York Times article revealed that “More than 2,500 of the 3,250 walk buttons that still exist function essentially as mechanical placebos.” Like in a lot of cities, these buttons are leftovers from older, less high-tech traffic management systems. Pre-1970s, traffic in the city was lighter, and could be managed without a supercomputer and a team of traffic engineers. Back then, these buttons really did make a difference. Nowadays, just 120 of them are pedestrian actuated, but it’s impossible to tell which ones are which, just by looking at them. So, my advice is to PUSH THE BUTTON. It might not always help, but it won’t harm your chances of crossing either.

--- Read the original piece over on Forbes