http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/pub...
I don't know what, if anything, this implies for autonomous truck speeds, but it's something.
Freight trains in Europe are much faster[1] -- but that could be because they often need to fit in with the schedule of passenger trains using the same lines (which themselves require the track to be maintained to a high standard).
[1] Citation needed, I only have observations of them going at a decent pace through stations I'm waiting at.
Intuitively, I'd expect that once the train has accelerated, it will keep its momentum very nicely, and (if electric) can easily return energy if it does need to slow down.
I can't find a real-world coasting distance for a train on level track, only reports during accidents/near misses -- 5km under emergency braking on a slight downhill slope, for one! [2]
[1] https://en.wikipedia.org/wiki/Rolling_resistance [2] https://www.gov.uk/government/uploads/system/uploads/attachm...
Then to stop it will take t = v/.0004g which means that you will travel vt/2 in that time.
For example, if a train is cruising along at 30 mph (44 fps) then it takes 44 ft/s / .0004(32.2 ft/s^2) = 3416 seconds to stop which means that the train travels 14.2 miles under ideal conditions.
http://www.coyoteblog.com/coyote_blog/2008/02/european-vs-am...
That's probably exactly why freight trains are faster in Europe:
> In fact, the freight rail system is so efficient that to some extent we've obviated the need for the Panama Canal. Many Asian container ships bound for Europe actually make port in Seattle or Vancouver, offload their containers onto trains which shoot across the country to New York or another eastern port where they are reloaded on ships for the trip to Europe.
Though I suspect soon enough the Northwest Passage will be clear for enough of the year that most freighters will just sail through the Arctic. Perhaps both Panama's government and North America's railroads should be pushing hard for a carbon tax.
If driverless cars are a "thing" in the future then what is Uber's USP? Why would you use Uber rather than one of a dozen other companies? Is it just their capital advantage? Their network of now unemployed drivers? Just the name and nothing else?
What is it exactly that keeps Uber in business with driverless cars?
In rural areas, an autonomous vehicle would need to travel long distances to pick up and drop off folks. It could be prohibitively expensive or inconvenient. People also use vehicles for other things in these areas, both work and play, which do not fit into the taxi model.
In suburbia, the taxi idea could work, but there might be advantages to owning your own vehicle. Maybe a family will own one autonomous vehicle, just one, but it would be in constant use throughout the day: mom goes to work, dad picks up donuts for coworkers, son goes to school, daughter goes to soccer practice, son goes to track practice, dad goes to get groceries, mom goes to get dinner, son goes to friend's house, daughter goes to football game, mom goes out to gym, etc. You'd have your one family car zipping back and forth between all these events in the family, picking people up, dropping them off, going off to do something else, and coming back again. Having an autonomous car in the family could make sense depending upon the costs.
* Why not put it to work. It could transport people or packages during that time.
* Mostly, in such a future, you probably won't own a car. You'll rent or lease access, and the price to take a nice autonomous mini-bus will be super low while remaining convenient.
I also think truck drivers already adjust their speed depending on economic reality. If, say, you are transporting fresh flowers towards an airport, arriving in time is more important than when you are transporting furniture to a furniture shop.
That certainly is true at the extreme ends. Drivers who drive to be transplanted organs between hospitals get special training to drive fast, while drivers driving garbage to a landfill likely will not be pressed for a timely delivery (although I do not rule out that someone who knows the latter business will tell me that missing one's reserved spot for delivery at a landfill can cost a lot of money)
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.
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.)
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.
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).
Could you, in the same situation, also get a ticket for following the traffic—i.e. breaking 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.
http://www.mit.edu/%7Ejfc/NMA/730CMR.html
Most of I-93 in NH has a posted minimum of 45.