> Minimum speed limit? As far as I'm aware, in the US you are supposed to go the posted speed.

The posted speed is usually an upper bound (though in some cases only a presumptive one, not a conclusive one, the way the law is actually written.)

> You could get a ticket for going slower if you are impeding traffic trying to safely go the posted speed.

You can get a ticket for impeding traffic, but usually going slower than the limit is not sufficient for that. (And may not even be necessary.)

> Are there roads in the US that specifically allow a range of speeds (beyond the variation seen because human drivers don't follow the law)?

Every highway (which is much broader than freeways) in California that doesn't have an expressly posted minimum speed limit, plus every one that does have an expressly posted minimum speed limit that isn't identical to the posted maximum limit. (California Vehicle Code Sec. 22400 allows a minimum speed limit to be established and posted -- which is still, where established, a soft limit -- and provides a violation for impeding traffic with or without such a limit, but does not set the posted maximum speed limit as a minimum speed limit, soft or otherwise, where no minimum speed limit is posted.)

Part (a) of VC Section 22400 is what I was remembering from way back when I took driver training, and it states "No person shall drive upon a highway at such a slow speed as to impede or block the normal and reasonable movement of traffic, unless the reduced speed is necessary for safe operation, because of a grade, or in compliance with law."

Wouldn't driving below the posted speed limit when there are no hazardous conditions fall under "as to impede or block the normal and reasonable movement of traffic"?

> Wouldn't driving below the posted speed limit when there are no hazardous conditions fall under "as to impede or block the normal and reasonable movement of traffic"?

Not normally, driving below the posted maximum speed limit would not, in and of itself.

It might -- and, given the soft nature of upper limits, it might even without driving below the posted maximum -- in the presence of other traffic, depending on the road (what will impede traffic on a single-lane road is different than what will impede traffic on a multilane road) and particular traffic conditions.

I understand that, but I guess I'm of the opinion that while we provide leeway to humans because of our nature, an automated system that drives below the speed limit in the case that it is blocking or restricting traffic be reducing the number of lanes flowing at full speed really has no excuse, other than purposefully slowing the normal flow to save money. I imagine that might be successfully litigated.

Could/would they drive well below the speed limit without legal problem when no traffic is around? I imagine they could, but I'm less interested in that (but understand my question was ambiguous).

Sorry, let me confirm this. You can get a ticket for driving slower than traffic, despite driving at the speed limit?

Could you, in the same situation, also get a ticket for following the traffic—i.e. breaking the speed limit?

> You can get a ticket for driving slower than traffic, despite driving at the speed limit?

Some speed limits in California are soft (it depends which of the provisions allowing speed limits they are adopted under, or whether they are the default limits.)

It is legally possible for traffic to exceed the speed limit where those limits are soft without necessarily being illegal, unreasonable, or safe.

It may, in some circumstances, therefore, possible to impede reasonable flow of traffic while driving at the speed limit in those cases, thus breaking the law.

> Could you, in the same situation, also get a ticket for following the traffic—i.e. breaking the speed limit?

Yes, but if the circumstances were such that someone could be impeding traffic at the speed limit, it would also necessarily be true that it would possible for you to exceed the speed limit and not be breaking the law. But the burden of proof would be on you to show that the driving was safe.

Yes, and in states with a 'basic speed law', or similar, you can even earn a ticket for driving substantially below the posted speed limit. The Utah driver's handbook and license test, for instance, explicitly call out that road conditions may be such that the maximum safe speed is 0 mph.

Massachusetts Turnpike has a minimum speed of 40 unless you are in a tunnel where the minimum is 20.

http://www.mit.edu/%7Ejfc/NMA/730CMR.html

Most of I-93 in NH has a posted minimum of 45.

Some states (forget which I was driving through) have posted minimum speeds on highway.

Others I'm sure there is a generic lower limit "clause".

I've never seen a state that didn't have a "at a speed safe with current rode conditions". So, that you can still get a ticket going 65 in a 65 but there happens to be a blizzard going on.

I doubt any state requires you to go exactly the posted speed limit.

There are cases of people getting obstruction of traffic tickets for going at the speed limit. It happened in Toronto. One guy got a speeding ticket in the merge lane, so in a pique he did the posted limit in the fast lane, which normally moves 15-20 mph faster than the limit. He caused a traffic jam and got an obstruction ticket. He fought the ticket and lost. Sorry, can't find a link now.

Many roads also have signs and states have laws along the lines of stay right except to pass. So if you're not actively passing in the left lane, you're breaking the law in many places even if you're going at the speed limit. I expect few tickets are given out for this even though it causes dangerous behavior.

In Missouri, we have signs posted where the Speed Limit is 60 or 70 and the Minimum is 40.