That depends on what state they're driving in. Some states (such as California) are especially stringent about a driver's logbook showing a lower average speed than the speed limit. Others, not so much. In a state where the terrain is relatively flat, you'll tend to have a higher average speed than a state which has lots of hills or mountains.
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Average MPH? There really isn't a "legal" average MPH.
Say you're hauling Budweiser. If you haul it out of Columbus, Ohio, your average MPH is going to be higher than if you haul it out of St. Louis because the place you pick it up from in St. Louis is farther from the Interstate than the place you pick it up from in Columbus. More city driving equals a lower average MPH.
You can legally drive 11 hours in a 14-hour period every day. How fast you go depends on where you are.
Yes, drivers with an international driver's license can legally drive in California for a limited period of time.
In most states in the United States, you can legally drive at the age of 16 with a valid driver's license.
Yes, a driver's license is required to legally drive a vehicle on public roads.
Yes, in most places, you need a driver's license to legally drive a car.
Yes, in most states, you need a driver's license to legally drive a moped.
Yes, in most places, you need a driver's license to legally drive a vehicle.
Legally, NO
In Idaho, you can legally drive at the age of 15 with a learner's permit, and at the age of 16 with a driver's license.
Yes, if you are a resident in Spain, you need a Spanish driver's license to drive legally.
Yes, in most places, you need a driver's license to legally drive a vehicle on public roads.
Yes, in most places, you need to have a valid driver's license to legally drive a car.
Yes, you need a valid US driver's license to legally drive in the US.