Hacker News Reader

Comment by sandermvanvliet | Hacker News Reader

Out of curiosity (and not really related to the article) but I’m kind of surprised to hear there is a formula for calculating how long(?) yellow lights are on and that it relates to a red light camera. AFAIK those cameras are hooked into the control system and only activate when the light is red, which seems like a pretty binary decision. Can someone shed some light on this?

View on HN

The yellow light provides a period when drivers know the light is going to go red soon, all else being equal this light should be set to stay on for just long enough for drivers in properly maintained cars, who drive at legal speeds, to see it and all either come to a stop or pass the intersection before the light turns red. Typically formulas care about the allowed speed of cars, the expected braking capability of a car that's allowed on the road, the gradient (down hill it's hard to stop quickly!) and other factors, plus the size of the junction (a huge junction can't change as quickly because it takes time to cross the junction).

That is, Sally is doing 40mph in a 40mph zone, she sees the light turn yellow, and she's very close to the junction so she just keeps going, everything is fine. Bob is doing 25mph in a 55mph zone, he's some distance from the lights, they turn yellow, Bob stops normally as the lights turn red.

With red light cameras providing revenue there is an incentive to cut that time too short. Now Sally finds the light turned red earlier and she got a ticket. So next time Sally won't make that mistake, as soon as the light goes yellow she slams on the anchors, and somebody goes straight in the back of her - there's a traffic accident even though we invented these lights to reduce accidents. Oops.

Now a _good_ government would resist the temptation. They would set the formula to reduce crashes. But money is very tempting. Shaving a second off the time, getting $1M of extra revenue and oops smashing up a thousand people's cars, that's a good deal so long as you aren't paying for all those car repairs...

The heart of the problem is that traffic cameras assume guilt.

Having constantly vigilant eyes watching for anyone to do one exact thing wrong is totally unreasonable, because those eyes to not announce their presence, and the definition of "wrong" is not directly quantifiable.

Police focus too much on quantifiable things like speed, where there is a lot more nuance to the surrounding situation.

I came to say basically the same thing - only your reply is much better worded and detailed than mine would have been.

In the age of big data optimizing for the right value will be our greatest challenge.

The question becomes "what is the right value?"

Is it "optimise for most money and fewest/no crashes"?

Or is it "optimise for fewest accidents"?

I can almost guarantee it will be the first option that is selected.

Yes I should have phrased that as "In the age of big data selecting the value to optimize will be our greatest challenge."

In Oregon, yellow essentially means stop. A lot of Oregon transplants (and apparently many commentators in this thread) aren't aware of this.

http://www.oregonlive.com/commuting/index.ssf/2014/02/joseph...

https://www.oregonlaws.org/ors/811.260

Oregon has lost of dumb laws. This one makes people less safe.

I'm sure the cameras are integrated into the control system. I believe problem is with the timing of the yellow light. If I made a light yellow 0.5 seconds on a road where people are traveling 35 mph, it wouldn't be possible for cars to stop.

Reply on news.ycombinator.com