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Comment by woobar | Hacker News Reader

> they drive the speed they feel comfortable with, regardless of the speed limit

My anecdata does not support this. When roads are not congested, I can see that most drivers accelerate from ~70+mph to ~80+mph right ofter the speed limit sign changes from 60 to 70.

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I think what you're seeing is that most people know that up to 10mph over the limit is pretty safe in regards to getting a speeding ticket.

That's separate from how fast they think is safe on the freeway in general from a physical standpoint. If there were no limits posted, they'd go even faster.

So basically I'm saying that both you and the parent poster are both correct. It's just that more than just physical safety is being taken into account.

The claim that the average speed at which people drive depends on the speed limit, and the claim that it does not, cannot both be correct.

They're both correct, or both wrong, in that both of their reasonings are correct in having a noticeable effect on thd outcome, while their conclusion may not be.

Yes, because they are comfortable at higher speeds than what is posted. Just that they'd rather only drive +10mph of what's posted to avoid speeding tickets.

Usually when the speed limit bumps up from 55 to 65, it means the stretch of highway is actually more safe. Whether it is a long straight away with few on/off ramps, or the end of construction - the jump in speed limit usually does correspond to the level of safety of the upcoming stretch of roadway.

Well, they have a speed they're comfortable with, AND an amount over the limit by which they feel (legally) 'safe' at.

All this proves is that they don't want to go much more than 10 over the limit, AND the speed at which they feel safe is at least (but maybe higher than!) 80mph.

I wonder if there is some kind of "steady state" vs "transition" effect that could explain this though. For instance, if you put up a sign that changed the speed limit from 70 to 80 but changed nothing else about the road, would you see an initial increase and then decrease after a few miles? Although I'd also guess that in reality if the speed limit changes to 80, there's probably other characteristics of the road that change so that the steady state might not regress back in this instance.

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