Oops, I read this backwards. The car should use the minimum speed limit from its set of stored speed limit signs, rules about local roads, and what it sees. I

Oops, I read this backwards. The car should use the minimum speed limit from its set of stored speed limit signs, rules about local roads, and what it sees. If the car sees a speed limit sign that's "too high," it should call back to the mothership for a proper investigation (by the autodrive maker or the local police or both). OLD POST (where I got your situation reversed): It _should_ drop to 25 mph, because maybe someone in authority put a real 25 mph sign there. Then they should investigate who did that. The countermeasure would be to take over the wheel. The eventual countermeasure would be to have the speed limit sign broadcast its number over radiowaves, which is of course still something people can mess with, but requires a higher bar than a can of glue.