If a receiver loses the signal from the radio, it may continue to send whatever the last command was. For example, if you're accelerating while turning left and the receiver loses the signal, your car may continue to move at that speed and turn left, which results in your car moving in a circle. Most commonly, though, the steering is at neutral (pointed straight ahead) and the car is under heavy acceleration. In which case, you better be a fast runner or have a big wallet! Otherwise your car will eventually smash in to something. This can be nearly prevented by purchasing a fail-safe, which will return the servos and/or speed control to neutral, or possibly even apply the brakes.