Each bridge sensors covers 14.5 inches of the track lane width. For example, if the track is 10 feet wide, 8 sensors will be needed. Simply divide the total width in inches by 14.5 to get the number of sensors needed. Generally speaking, it is OK to go a little over. A 4 foot (48 inch) lane calculates to 3.3 sensors, but 3 will cover it sufficiently. The number of bridge sensors needed is only determined by the width of the lane, and it does not matter how many transponders are used.