Particle catchers are polycarbonate panels embedded with pairs of conductive metal strips which measure resistance between them. The panels are positioned at an angle to the ground and are designed to get progressively clogged up as roadside dirt accumulates. Automatic neoprene rubber wiper mechanisms clean the panel surface after a given percentage of sensor strip pairs are triggered by accumulated material. During wiping, a data pulse is transmitted and then the process starts again. Note: rainfall will also trigger the sensors.