When a passenger in car or bus or train or airplane, my right leg is a problem within 30 minutes. On Sunday night I was a car passenger for four hours without a problem. What I did was to raise my right leg as far as possible 40 times every 15 minutes. Before the trip started I walked briskly for about ten minutes.
During a later part of the trip, I waited until my leg started to feel bad before raising my leg. Even when doing it continuously, that did not solve the problem. Apparently preventing the problem is easier than solving the problem.
Note: this only works if I have not taken significant caffeine in the last 6 hours.