Cars on roads must be counted using metal detectors. There are two technologies: inductive loop or magnetometer. A loop is installed in the road surface itself. This requires a petrol-driven disc cutter and resin or hot tar to seal over the grooves where the wire has been looped. Its advantages are that vehicles are only sensed when directly over the sensor loop and the battery requirement is minimal. Linetop also makes preformed inductive loops from tough multicore cable which can be buried in gravel roads provided that the surface is well enough compacted to immobilise the cable totally.
Whereas an inductive loop will need highways authority permission and a paid-for licence if the road is a public one, a magnetometer would be buried in the grass verge which is usually private land with an amenable owner. The magnetometer sensor element is finger-size and it is buried immobile as close to the tarmac as possible. The data logger can be buried a few metres away in a safer position for retrieving the data in its memory cube. It is essential that magnetometer elements are totally immobile in the ground and cannot move or heave. So raised banks are ideal.