How many miles driving per day is considered unsafe for professional drivers?
Commercial drivers are limited to 14 hours of work in a 24 hour period. Of those 14 hours, they are allowed to drive 11, and up to 2 additional hours in an emergency situation brought about by unforseen problems (snow blizzard to get to safety).
The max speed limit in US is about 75 miles an hour. Giving time for stopping, starting, traffic, etc, the average speed of a driver will be somewhere around 65-69 miles an hour. You can figure it out from there. Some states, CA, OR, WA, IL, IA, IN for example have lower limits for big trucks.
This information on the hours of work is found in the FMCSR by Department of Transportation. That’s Federal Motor Carrier’s Safety Regulaions. In addition, each state has their own rules.
CA has not, to my knowledge, adopted the Fed’s rules yet.