The law states that you can not medicate in a moving vehicle. As long as you are not near a school or the othe areas stated that are no smoking in prop. 215 you should be fine.

.....11362.79. Nothing in this article shall authorize a qualified patient or person with an identification card to engage in the smoking of medical marijuana under any of the following circumstances:

(a) In any place where smoking is prohibited by law.

(b) In or within 1,000 feet of the grounds of a school, recreation center, or youth center, unless the medical use occurs within a residence.

(c) On a school bus.

(d) While in a motor vehicle that is being operated.

(e) While operating a boat.