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Comment by fleitz | Hacker News Reader

Another great example of money trumping public safety is red light cameras, it's well known that the best way to reduce intersection fatalities is to increase the time length of the amber light. However if you take the average amber length of a red light camera intersection it is below the average length of non-red light camera intersections.

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The only studies that show that an increased amber length decrease fatalities have a study period of less than 10 years. Other studies have shown that the effect dissipates after 10 years as drivers adjust to the longer yellow by driving through them.

I hate long yellows, and even worse is the "all red" period some cities have added between the yellow and the next light turning green. It makes traffic inefficient for people who follow the law (which says you must stop at yellow lights) and it vastly increases the number of people who blow late yellows and even reds.

Yellow lights (and all-red periods) are useful because drivers need a transition time between "go" and "stop" to allow them to react safely. Demanding that all drivers always stop at all yellow lights effectively turns the yellow light into a red light, and drivers are forced to switch instantaneously between "go the speed limit" and "stop."

All-red periods are also useful at intersections where traffic backs up and blocks the intersection for a few seconds, not because drivers entered the intersection when traffic was stopped, but because events down the street or at an adjacent light may cause traffic to stop suddenly with drivers already in the intersection.

In Germany you are only supposed to drive into an intersection, when you can pretty much guarantee that you can leave it.

From what I understand, this is true in most states in the U.S. -- you're considered to have run the red light if you haven't exited the intersection by the time it turns red.

There seems to be some confusion about this. Most people I've talked to think that if you make it past the intersection entrance line before the light turns red, you're fine.

Demanding that all drivers always stop at all yellow lights effectively turns the yellow light into a red light, and drivers are forced to switch instantaneously between "go the speed limit" and "stop."

I don't know about where you are, but here amber lights mean "Stop if it's safe to do so", i.e. if the choices are go through the junction or slam on the breaks, you should go through the junction. If the choices are to stop smoothly and safely or go through the junction, you should stop.

Yellow lights are useful, for the reasons you mentioned. My beef is with long yellow lights.

And I disagree with your justification for all-red periods. If you're stopped in the middle of an intersection because of a blockage, it usually takes a lot longer than 1-2 seconds to clear the intersection.

I'd be hesitant to imply causality like that. Red light cameras could be very well placed at high accident intersections as an attempt to reduce accidents. (I'm not claiming their effective at it, but that could be one of many reasons they're placed there.)

Several studies show causation.

http://beta2.tbo.com/news/nation-world/2008/mar/12/na-red-li...

I'm too tired to find the cite now, but Car and Driver has done numerous articles on this subject. In fact, the contractors who run red-light camera systems have sometimes prevailed on authorities to reduce yellow-light durations on camera-equipped intersections to increase the violation rate.

These systems are usually run by contractors, who include a guaranteed-revenue clause in their operating agreements. If the cameras are actually effective in stopping people from running red lights, then the operators will go back to the local government to demand that they make up the shortfall.

All in all, a dirty business that's clearly not safety-driven.

At some point the preponderance of evidence is such that is the authorities' responsibility to prove their side of the case.

http://blog.motorists.org/6-cities-that-were-caught-shorteni...

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