The tornado in Newton county (Oklahoma/Missouri) was moving 50-60 mph. A thunderstorm passed 20 miles south of me last night moving 55 mph according to NWS radio, and any embedded tornado would move at least as fast. The funnel can "wiggle" even faster than these average speeds, especially if it's on the "fast" side of a supercell thunderstorm.

The real problem is the roads. You can't always drive 60 mph on a narrow country road in a thunderstorm with other panicked drivers trying to do likewise. It's not the same as trying to do it under ideal conditions, especially if the country roads just aren't maintained for those speeds (potholes) or not flat & straight enough.

I have a CB/NWS weather radio in the car and if I must be out in bad weather I tune into NWS. Were a tornado spotted near me and no other shelter available I'd probably look for a culvert to crawl into and a stick to "ask permission" from the culvert's residents, and crawl in if the tornado got within a few hundred yards.