Final answer:
When your car stalls or breaks down on the highway, it is generally safest to stay with your vehicle and have someone else find help, using hazards and safety devices like flares or reflective triangles to alert other motorists.
Step-by-step explanation:
If you stall or break down on the highway and cannot restart your vehicle, the safest option would be to stay with your vehicle and have a responsible person go and find help. This ensures you're not leaving your vehicle unattended, which could be dangerous for you and other road users. If it is safe to do so, you should move your vehicle to the side of the road, turn on your hazard lights to alert other drivers, stay in the car with the seatbelt on if you're in a risky spot, and wait for help to arrive. If you're able to place reflective triangles or flares to further alert incoming traffic, do so. It is crucial to assess the situation based on the level of safety and whether or not leaving the car would increase dangers. For instance, staying inside the vehicle might be safer if you're broken down on a busy highway with fast-moving traffic, whereas if you're in a quiet neighborhood, it might be safer to exit the vehicle and wait at a safe distance. Always remember to contact emergency services as soon as possible.