Ask MetaFilter questions tagged with speedlimit

Does the optimal speed for fuel efficiency vary by car model?

scblackman — Fri, 11 Jul 2008 07:24:14 -0800

What is the optimal speed for fuel-efficiency for my car? Do I really have to drive 55? As I've been listening to the increasing buzz about resurrecting a national 55 MPH speed limit, I starting thinking about where that number came from, the types of automobiles in use at the time the number was derived, and whether it is still applicable today.

From what I understand, above 55 MPH is the point at which wind resistance increases drag enough to cause a disproportionate increase in the amount of fuel consumed in order to move the car a certain distance. Of course, that was what we were told in the 1970s when people were driving Lincoln Continentals and El Caminos. Cars today are supposed to be engineered to be more aerodynamically sound, thus less drag.

So my questions are these:

- Does the optimal speed for fuel efficiency vary by car? Will my Honda Fit be just as efficient at 65 than at 55, where a Land Rover won't?

- Are there any sources of data (tables, etc.) by car model that would have this data?

- Are there other factors that I'm missing besides, wind resistance, that contribute to fuel inefficiency at speeds greater than 55 MPH?

Traffic Technicalities Times Three

vanoakenfold — Tue, 22 Aug 2006 07:59:51 -0800

A flurry of interrelated USA speed limit questions: At what point does the speed limit (USA) become so, at the point of the sign, when you see it, or when you gradually acc/decelerate that far?

Relatedly, do the exit/offramp yellow-sign speed limits actually count? How do they expect me to go from a freeway 60 to an offramp 30 and back to an access road 50? Is this implausible 30 just a recommendation, or can I actually get ticketed for doing 60 in a 30 on an offramp?

Smart-a$$ily speaking, I have never seen a speed limit on an on-ramp -- does this mean I can go 220 until I see a speed limit sign?

Has anyone noticed traffic information painted directly on the streets outside of Mountain View?

Jeff Howard — Mon, 27 Dec 2004 12:45:52 -0800

I was in Mountain View recently and noticed speed limits painted directly on the streets. Anyone else seen this kind of thing? [+] A big "35" was painted on each lane of the street. It took me a while to realize that they were speed limits instead of road numbers. The latter are more common in my experience. For instance, on 1-70 through Columbus, Ohio there's a point where the road splits, and a big 1-70 is painted on the appropriate lanes. That made sense to me, but speed limits seem pretty much out of the norm and a little confusing.

Anyone familiar with other instances of speed limits or other meta-information incorporated directly onto a road surface? I've Googled for this and come up with some examples in England, but nothing else in the US outside of California.