A car ramp provides a simple method of raising a vehicle from the ground in order to access the underneath of the vehicle, it's one among the three easiest ways to elevate a car, together with the other two:using a jack or using jack stands.
The most important point of the car ramp it's safety, for cars can be kept very stable on top of them. Some types of these ramps can be built at home hand-made with simple tools.
References
Car ramp Wikipedia(Text) CC BY-SA