Assuming that you are using Scalextric track.
With an analogue track cars stay in their lanes and are propelled by their motors as their lane is powered when a controller trigger is pulled.
Digital racing is different as the lanes are permanently powered and the cars are controlled with a digital signal sent to a chip within the car to send power to the motor. They can also switch lanes for overtaking etc. when a signal is sent to lane changers within the track rails.