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Comment by Eikon | Hacker News Reader

We have the same thing in France but to prevent speeding when a light is about to go red.

On some lights, there’s a speed sensor, if a car exceeds the speed limit, it instantly goes from green to yellow then red.

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It's actually not that dangerous. Where I am the speed is measured about 200-300 meters from the traffic light. The traffic light changes when you are at a point where you can still slowly come to a stop - you won't be anywhere near a situation where the light changes to yellow as you are about to enter the intersection.

That...sounds dangerous.

I presume the red is unilateral, meaning they don't (immediately) change the other side to green in response.

Yeah that makes it a lot safer. But still, what if two cars are approaching the signal and they end up rear ending?

Even still, much like in India where drivers will learn to ignore the the punishing light, it could be drivers in France will learn that running reds does not increase a chance of collision because it’s only a signal of speed.

Increasing a chance of collision or not is not the same as losing a minute over a traffic light or annoying a few people. It does not appeal to the same emotions, it has a much deeper meaning.

I believe the comparison is flawed.

It only has to increase the chance of getting a really expensive ticket and points on your license to discourage that.

When a light turns yellow, a driver has to make a very quick calculus of a number of factors, including estimating stopping duration and distance, traffic presence, penalties, even judgement from other drivers. Some people will place more weight on one or another of those factors. If there is any significant portion of the population that places weight on "this isn't a real red light; it is only meant as a nagging signal" then it seems that the chances of a miscalculation (and high-speed collision) become greater overall.

The obvious solution would be to combine each nagging signal with a red-light camera, at which point it becomes very "real".

How would it be more dangerous than triggering the transition by a timer?

If it's unpredictable, can I end up being rear ended by someone behind?

Because humans anticipate things and this simultaneously changes their intuition about the light they're anticipating after confirming that it's particularly relevant, essentially maximizing the chance the run a red light, or slam on the brakes and get rear-ended.

perhaps if the sensor is not on the light, but some distance away that would be a lot safer? (I don't know how it has been arranged)

Placed some distance away. Happens also in Spain next to schools or hospitals. Is designed in special casses when humans need to use often a crosswalk, not to manage trafic in a crossroad. It works well.

Sounds overly complex? We just have combined speed-and-red cameras here. So if you go 70 instead of 50 to make the light you're getting a speeding ticket. Still cheaper than a red light ticket, but not by much.

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