Mountain bikes on purpose-built single-track used only by cyclists can be counted using a buried pressure slab. If the track is multi-purpose then the bikes must be metal detected using a magnetometer or an inductive loop, in the same way as cars but on a smaller scale. Sometimes one wants to count cars on a site road but not bicycles, or motorcycles but not bicycles, and our metal detector sensitivity can be adjusted to react to only larger objects. A magnetometer element or inductive loop must be fully immobilised in the ground. So in some soft surfaces, such as forest paths, it may require a small concrete block to be buried in the trail.
On a multi-user trail, such as a forest road with vehicles and walkers as well as bicycles, the only way to count bicycles is with an inductive loop, as in the photo left. The cyclists and walkers, but not the forestry vehicles, can get through the gap between the posts. But only the bicycles will set off the metal detector and trigger the counter. The new gravel near the posts is a concrete mix to ensure the inductive loop does not move. The large gate is normally locked.
Some trails have a hard surface which does not suit buried pressure slabs, or they are a bit on the wide side, or they are multi-use. In such cases it may be easier to bury a magnetometer, as in the photo left. This is a sausage-size sensor on a cable that reacts to iron. There is usually enough iron in most bikes, even quality ones, to set it off when buried in the middle of the track.