The TMA-122 detects vehicles approaching the stop line, over a distance of 20 or 60 m. Two relays are activated: one when a vehicle is moving in a zone 20 or 60 m before the stop line, the other when  a vehicle is moving or stops in a zone (adjustable) of 10 m by default before the stop line. The “traffic light presence” relay is maintained, within the hold time, until the vehicle restarts.

This relay is switched for each vehicle that passes the stop line. The information thus transmitted to the automatic device can then be easily converted into counts. If a vehicle does not move when the traffic light turns green, the control device is informed of a possible intersection blockage.