[Binghamton_native]

And to add to your excellent point, for those driving long distances, perhaps across country, obeying the 55 mph limit will probably mean an extra day on the road. So now where are the dollar savings? In addition, what are the consequences for long distance trucking if the trucks are also forced to a lower speed?

If fuel is saved at a lower speed for autos, is fuel also saved if planes fly slower? If so, perhaps Congress should also edict a top speed for jet travel. /sarc.

[supercat]

If fuel is saved at a lower speed for autos, is fuel also saved if planes fly slower? If so, perhaps Congress should also edict a top speed for jet travel. /sarc.

FYI, planes have different speed limits and optimal speeds depending upon one's goals:

1. Structural speed limit--go too fast and the airframe will break apart (not all designs can reach this limit, even in a power dive)
2. Stable speed limit--go too fast and the plane may become uncontrollable (not applicable in all designs)
3. Level top speed--drag equals maximum thrust.
4. Optimum speed (fuel per mile)
5. Optimum speed (fuel per unit time)
6. Minimum level speed

It's worth noting that efficiency per mile drops off significantly below the first optimum speed; it drops off precipitously below the second. Some types of acrobatic planes could fly at 5mph, but they'd use enormous amounts of fuel to get anywhere at that speed.