These devices are often referred to as žpadsÓ in the road, but nothing could be further from the truth. They are in fact, made up of a roughly rectangular shaped wire loop, laid repeatedly around the rectangle to create a coil and then a miniature magnetic induction field is created above, so that when a metallic vehicle passes over this magnetic induction field, its presence is detected and throws a pulse switch 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 and žout of hoursÓ only the 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 žvehicle still presentÓ mode to act as a safety device, as opposed to a switching device. Induction roadloops are often fitted in conjunction with other forms of switching.