Final answer:
It is never legal to consume cannabis products inside a vehicle, even if prescribed by a doctor or while stopped at a traffic light, due to safety and federal regulations.
Step-by-step explanation:
It is never legal for a driver or a passenger to consume cannabis products while inside a vehicle, regardless of whether the cannabis was prescribed by a doctor or if the vehicle is stopped at a traffic light. While medical marijuana can be legally prescribed and consumed in many regions, the act of using it while in a vehicle is prohibited due to the implications it could have on driving abilities and the safety of others on the road. This rule aligns with federal regulations and the Controlled Substances Act, which still classifies marijuana as a Schedule 1 drug. The legality of medical and recreational cannabis varies from state to state, yet the consumption within a vehicle remains illegal under all circumstances in order to maintain traffic safety and comply with federal guidelines.