I have a lot of opinions about traffic lights, mostly relating to the highway code and cycling. However this is a small point that I've considered for a while. To me it makes an interesting point about common sense developing an illogical system; interestingly should someone provide evidence in the comments against my point it proves that logical overthinking of a system produced by common sense could be equally misleading.
Consider traffic lights at a pedestrian crossing. The following series of events occurs:
- A pedestrian intending to cross the road presses the button at the crossing.
- After a (seemingly random) length of time the traffic light cycle begins for the cars:
- The green light switches off as the yellow light switches on
- There is a pause to allow for cars too close to stop
- The yellow light switches off and the red light switches on
- There is another pause to allow for idiots to run the lights [link removed, you know what I'm talking about]
- The red man switches off and the green man switches on
- After another length of time, or after cameras detect that nobody has decided to sleep in the middle of the crossing, the process reverses, except with a flashing yellow light.
- Should the crossing be activated again an extra delay may occur before cycling to allow for a sensible traffic flow.
The process seems obvious and safe but it leaves me with one question: why does there need to be a delay between a pedestrian requesting the crossing and the light cycle beginning?
Of course, obvious answer - if the lights changed straight away cars wouldn't have time to slow down. But no; re-read the process again and you'll see that this purpose is already served, by the transition to the yellow light. Regardless of a delay, the first indication cars get that they need to take action is that the light changes to yellow; this is instantaneous - at a certain point there's a state change and that is what necessitates their slowing down.
In fact, having a pedestrian stood at a crossing with no activity on the lights is detrimental to slowing cars down - people approaching on the road may see the pedestrian and actually speed up slightly, knowing that any moment (but not in which moment) the lights will change and they will be forced to stop. So, the initial delay cannot serve the purpose of slowing cars down, and in fact could go against this.
Another answer - if the lights changed immediately people could prevent the traffic flow. Less pertinent and more obvious to disprove; there's already an extra time built into crossings to allow for this; if the initial delay was removed, this could simply be increased.
A few other possibilities come to mind, but they are dismissable:
- Instant changing could be used with malicious intent - someone who wants to cause trouble will find a way, making traffic lights less effective for pedestrians does not help this.
- Seeing a pedestrian waiting should slow many drivers down - in both the highway code and driving tests drivers are taught to always slow down when approaching any crossing, junction or other hazard. Looking for people at a crossing is distracting, and furthermore the idea that if there is nobody visible the area is safe is counter-productive, when there's every chance that even when looking you won't spot someone.
In, rather brief, conclusion then, why does this situation exist? I can only assume it is because of the common sense fallacy in the first answer - that this delay is to slow down drivers, missing the delayed-instantaneous nature of the light's state change. Alternatively I've missed something obvious and I'd like to know why I'm the idiot here instead. Asnwers in the comments please!