Buried under the tarmac, these devices are made up of a wire loop, laid repeatedly around the rectangle to create a coil and then a miniature magnetic induction field is created above. When a metallic vehicle passes over this magnetic field, its presence is detected and a pulse switch is thrown to open the entrance. They are typically used on busy, accessible gateways to allow freedom of vehicle movement; sometimes for exit only, but sometimes loops are laid inside and outside to allow free entrance and exit.
They are often overridden by a timeswitch so that access can be restricted to certain hours. Out of hours only authorised users, with other forms of switching (e.g. remote controls), can pass through. The road loops are laid into special positions in the roadway, often being disc-cut into tarmac or concrete and linked back to the CAME control panel by twisted wires. Once installed, the sensitivity of the induction loops can be set to sense the types of anticipated vehicular traffic from a vehicle as small as a metal wheelbarrow up to an excavator. Induction roadloops can sometimes be used in a vehicle still present mode to act as an additional safety device. Induction roadloops are often fitted in conjunction with other forms of switching.