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Comment by terryf | Hacker News Reader

The speed limit example is a great one. Consider a road that has a 35mph limit. Now - which of the following scenarios is SAFER: a) I'm driving on the road in a brand new 4x4 porsche on a sunny day with great visibility and brand new tyres. Doing 40mph. b) I'm driving on the same road in a 70s car with legal but somewhat worn out tyres, in the dark, while it's raining heavily. Doing 35mph.

Of course technically option a is violating the law but no sane police officer will give you a fine in this case. Nor should they! A robot will, however. This is stupid.

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The Cayenne would be safer going 35 instead of 40 regardless of all other variables. It's a trivial physics question, kinetic energy is a function of mass and velocity.

I meant a 911 but thank you for answering a completely different point than what I was making.

The reason we have speed limits isnt due to vehciles being unable to 'handle' certain speeds though, it's to minimise the damage of an incident at that speed, which is entirely a matter of physics.

No, that is not true. I used to work on road signage systems, where we would use test vehicles, sensors, and math to figure out what the correct signage should be for various sections of road. The standards are primarily concerned with maintain a margin of error for the "worst" cars on the road, i.e. the ones that meet only the minimum inspection requirements. What happens once that margin of error is exceeded was anyone's guess, but practically could be wildly different for specific scenarios that had more to do with the off-road environment than the exact parameters of the road. Two roads with identical bends would receive the same signage regardless of whether under steering through the curve would land you on a sidewalk or in a field or over a cliff.

AFAICT at least 2 people in this thread don't seem to think that visibility -- a function of, among other things, weather and time of day -- influences driving safety. I find this amazing.

The point of terryf's example was to point out that for practical reasons, existing laws don't capture every relevant variable. I (but not everyone, it seems) think that visibility obviously influences safety. The point I want to make is that in practice the "precision gap" can't be perfectly rectified by making legality a function of more factors than just speed. There will always be some additional factor that influences the probability of a crash by some small amount -- and some of the largest factors, like individual driving ability, would be objected to on other grounds.

The Cayenne would not be safer going 35 instead of 40 "regardless of all other variables": it's statistically safer to go closer to the flow of traffic because you're then "at rest" with respect to other drivers (assuming a controlled access road without pedestrian traffic). If the speed limit is 55 and the flow of traffic is 70–80 (as is the case with the Beltway around DC, despite automated enforcement), then going 55 is more dangerous than "speeding". The issue with 100% enforcement is every law assumes certain circumstances or variables and the real world is infinitely more complex than any set of variables that can reasonably be foreseen by law (and laws that attempt to foresee as many variables as possible are more complicated and, consequently, harder for normal people to apply, which is another reason for latitude in enforcement).

safer for whom? Remember cars are not the only ones participating in traffic.

“assuming a controlled access road without pedestrian traffic”

such roads barely need speed limits. In some places they do not have them

The problem with your DC beltway example wouldn’t be automated enforcement then, but with the speed limit itself.

A road without pedestrians and intersections in it should have a speed limit that reflects the reality of its use (70-80)

"Regardless of all other variables"

Variable 1: The Cayenne is on a train track

Variable 2: The train behind the Cayenne is going 35mph.

You painted with too broad of a brush with that statement.

If there was an accident an officer might give you a fine in both cases where I live. In the Porsche case they can say you broke the law and were speeding that led to the accident. But also in the case of old car for failing to adjust your speed to your skills, the state of your vehicle and conditions of the road and weather regardless of the speed limit.

The classic. In Bulgaria they used to do that (and maybe still do). Every time there was an accident they'd often write up everyone for "speed not matching the conditions" with the idea that all accidents are avoidable, you just weren't going fast/slow enough so git gud and don't forget to pay in the next 2 weeks to get a discount.

Yes! This is exactly the point - machinistic enforcement makes no sense in case of speed limits. All laws about driving explicitly say that at the end of the day it's the driver's responsibility to drive safely and if they cause an accident, then they are at fault in some cases even if they followed the speed limit.

The point is that whether you drove dangerously is not a strict, machinistic "if-then" assessment. Automatic enforcement of speeding is ridiculous when viewed in this context.

And the people saying "yes but there is more energy in a faster vehicle" have clearly not felt the difference between driving a car with drum brakes vs modern brakes.

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