Which item is essential for a vehicle to have when parked on the side of the road?

When a vehicle is parked on the side of the road, it is crucial to have warning devices to ensure the safety of both the driver and other road users. These devices, such as hazard triangles, flares, or reflective vest, serve to alert oncoming traffic to the presence of a stationary vehicle, reducing the risk of accidents.

Having warning devices is especially important if a vehicle is not in motion or is stopped in a potentially dangerous location, as it makes the vehicle more visible to approaching drivers, especially at night or in poor weather conditions. While having extra fuel, a spare tire, and a flashlight can be useful in various situations, they do not directly contribute to the immediate safety of a parked vehicle on the roadside like warning devices do. Thus, the presence of warning devices is essential in this context.