From what I’ve seen covered elsewhere, the magnets don’t actually do anything for triggering the traffic lights.
What really works is getting the traffic engineers to tune the settings to trigger properly. My steel-framed bicycles with 27-inch diameter alloy wheels ought to work if they’re doing it correctly. My standard practice is to line up directly over the pavement cuts that show where the embedded loops are (not in the center of them). There are a relatively small number where this actually works, but not nearly enough of them.
I have found traffics signals in the UK to be very aware of bikes. When I lived Canada I often had to put my frame nearly horizontal to get it noticed, but not here.
The loop detectors have two common arrangements, single loop and figure-8.
If it’s single, the detectors are most sensitive at the outside edges of the detector. If figure 8, the most sensitive part of the detector is above the middle longitudinal cut, the outside edges are next-best
There was an intersection when I was younger where the sensor was ahead of the stop line. This just changed the lights for the cars - pedestrians still used the buttons and were unaffected. However it was not uncommon to have to get out of the car, walk up to the car at the light, and then explain and point to things.
In short I do not have a great deal of trust for installations of this sort of thing, even if well intentioned.
they’re essentially placebos meant to pacify pedestrians, the lights are all on timers anyway
Not in the UK. There are published standards for how they work and these include timings*. Without getting into excruciating detail (that’s what the standards are there for) once a pedestrian presses the demand button the pedestrian lights will turn green in between 10 to 66 seconds later, with a strong recommendation to never make it more than 36 seconds except in exceptional circumstances. This is for stand alone crossings, not ones that are part of a junction.
In the UK if the lights are timer controlled (such as at a traffic light controlled 4 way junction) then the demand buttons generally won’t make the lights change on demand, as there is a defined pedestrian phase built into the junction’s sequence, but may influence whether there is a pedestrian phase or how long it is.
At junctions with full demand sequencing based on traffic sensors then the pedestrian demand buttons do cause the lights to change, but it may not be obvious as the cause->effect relationship may be delayed by balancing all the input demands.
Most new pedestrian crossings have pedestrian presence sensors so the lights can cycle back to allowing traffic to flow as soon as possible after the crossing is clear of pedestrians. The timings on these are typically set to the minimums in favour of the pedestrians i.e. A pedestrian can cross 10 seconds after pressing the demand button.
*Department for Transport Traffic Signs Manual Chapter 6
Also in France (see my earlier post) on the exit from the ferry terminal there is a set of lights with a clear notice to pull up all the way to the lights (because of a sensor). Brits exiting tend to hang back so they can see the lights - there is no second set on the other side of the road, but like most French traffic lights there’s a mini set of them at window height, below the main set and facing the stopped cars, so that’s how you see when they change and how it is possible to pull right up to the lights. More than once I’ve had to point this out to some doddery idiot in front.
I am not in any way an authority on any of this, but I will say that thanks to The Knowledge in London, and the number of students riding scooters to solidify their mastery of the A-Z, it’s likely that any sensors would definitely take smaller 2-wheeled conveyances into account:
This varies dramatically all over the US, and even within neighborhoods. From my informal study, they come in the following flavors:
Buttons that insert a walk cycle into the normal car loop. If you don’t push the button, you’ll never get a walk light. When you do, the cycle changes to allow a longer green in that direction so you can cross. This is common in busy inner city intersections on large roads where the pedestrian needs a lot of time to cross, but pedestrians are rare so you don’t want the long cycle every time.
Buttons that interrupt the car loop to give you a walk. As soon as you push the button, the lights start the yellow cycle after a safety delay and initiate the walk cycle for you. This is common on streets that rarely have cross traffic, so they sit on green in the dominant direction until a pedestrian pushes the button (or a car is detected on the side street)
Buttons that used to do one of the above but were disconnected or disabled as part of a change in traffic management strategy. There’s no point in paying to remove the button, so they leave it there.
I doubt there’s ever any deliberately placebo buttons. I can’t see any reason they would pay to install such a thing.
By far the majority of scooter (and e-bikes) in London are ridden by food delivery riders (who are paid a per-delivery rate).
Not unconnected to this
motorcyclists were involved in a disproportionate number of collisions resulting in fatal or serious injury to other people given their share of traffic in 2020.
There have been a lot of reports over the years about the phenomenon of placebo buttons, though, as you suggest they may be more vestigial than installed for the express purpose of pacifying pedestrians.
Yah, I’ve read a lot of those stories, but never seen a reasonable hypothesis for why fake buttons are such a good idea that cities would spend millions to implement them. Nobody has a good reason for this, which to me shoots down the whole idea. If there was some study showing that pushing fake buttons reduced jaywalking or something, then maybe. But even then the effect would have to be so strong that the money spent on the buttons is less than the cost of the accidents prevented by them, which would be a very difficult case to make.
Considering all the huge, evidence-based, easy wins that exist in civic infrastructure that cities don’t spend money on (bike lanes, parks, traffic circles, etc, etc) the notion that all them are going around installing fake buttons is ludicrous to me. Cities don’t have a lot of money and are generally pretty careful what they spend it on, contrary to what cynical old men in public hearings think. City planners are not stupid.
