Why, if 55 mph limits were shown in the 90's to be useless, are we back to

[MissDeviance]

THAT again? I specifically remember during the late 1990's that there were 2 shows, one on 20/20 and another on Dateline, that talked about the "old 55 mph speed limits", because I asked my mom and dad about it at the time. They explained that way back in the 70's congress decided 55 mph was the most fuel efficient speed and that became the speed limit... even though most superhighways were specifically designed for 65-75 speed limits. (And I think one of those shows was really about how newer roads were poorly designed because they used the 55 limit, and meanwhile everyone was now driving 70-80 mph.)

One of the shows went on to talk about how today's cars are actually more efficient at the higher speeds, and that slower speeds (including 55) actually use more gas. And they backed it up with charts and experts and all that. They concluded the 55 limit was a manufactured hoax.

Now we're talking 55 again. More science by consensus again. Are we doomed to do the same nonsense again?

[single occupant]

No one has proved them useless. What happened was that on the majr highways, everybody simply decided that 65 was the new 55 and the cops looked the other way.

In fact, driving at that speed does save fuel. But people didn't want to do it and that's the basic and simple fact.

[billrussell42]

single is correct. Reducing speed from 65-75 to 55 saves 20% or more on fuel. That bit about cars being more efficient at higher speeds is totally wrong. Totally.

Actually, the most efficient speed is about 45 mph.

The problem is air resistance. Just put your hand outside a window at 70 mph and you know what I mean.

Drag due to air resistance goes up as the square of the speed. That means if you double your speed, the drag (and power needed) quadruples. This is hard science, no doubt about it.

[Rolyn eto]

The old 70 mph limits were made in the 60s when cars like Anglias, A40s and Heralds were around. They took ages to stop and their top speed was only around 80.
Now, 40+ years on cars can go at twice that speed and can stop in half the time/distance, yet the old archaic limits still stand. Drive on any motorway on a dry day and the majority of drivers will be driving over 70mph....safely. The vast majority of these drivers don't want to kill or hurt anyone and they don't want to risk damaging their cars, yet these drivers are regarded as criminals as they exceed some arbitrary, archaic limit.
Most drivers are sensible and would obey the limits if they were sensible eg 20mph past schools, 30mph through villages but saying that 80-85 mph on a dry road in a well maintained, capable, modern car is ridiculous. this is why so many drivers disobey it. I'm not saying that boy racers who drive at 60mph through villages or 50mph past schools should not get punished....they should, butcommon sense should prevail.