I think that Jesper probably intends to use a timer to triggerer a power up and poll of the sensor system. As such if he checked every 1 second he is unlikely to miss many cars. Unless of course the 6 meter length of the car passed by the by the sensor at a velocity of over 6 m/s (21.6 km/hr).

Obviously there is a need to consider the detection timing versus the speed of the vehicle but those factors seem that they would be easily adjustable within the parameters that Jesper has given.

Michael Karas