Coming down on a car roof is bad. Coming down on a person is way worse. Usually, it is the user setting up their detection zone wrong and/or not understanding their barrier’s design that results in a barrier arm coming down.
Induction loops
A loop is shaped like a wire rectangle. It is cut into the road surface to make a circuit. When a car (or other metal object) sits over the loop, it is detected. Barriers with loops usually do two things. The first is a safety loop which is under the arm and stops the barrier from closing if a car is still under the barrier. The second is a closing loop that is usually located near the barrier. The closing loop tells the barrier it is okay to lower and open.
Where loops go wrong is in the positioning and the sizing. Loops that are designed for cars, may overlook gaps between vehicles and lose a high-bodied vehicle, as the metal may be completely masked by the wheel arches. If your site gets trucks, vans with trailers or motorcycles, the loop layout must take them into consideration.
Photocells
Beams of light between a pair of photocells stops the barrier from closing. Break the light beam, and the barrier remains open. Loops can’t cover everything, and photocells can cover certain blind spots left by loops.
Loops don’t see people
A loop will only detect metal. Loops will not detect people. Walking under an arm will not register on a loop. Barrier lanes are not footpaths. A barrier lane should not be a shortcut. If people are accessing your worksite, provide them with a designated pedestrian route that is clearly signed, and do not allow a barrier lane to be a shortcut.
Keeping it working
Loops can be damaged by resurfacing, potholes, and cracks in the road. Photocells can get knocked out of line or get dirty. A barrier that has worked safely for a number of years can, after resurfacing a contractor, lose its safety assurance. Test the safety devices at every service and after any resurfacing work on the road.
Back to the full guide: Car Park and Vehicle Barriers