The TunnelCraft 3 CO/VIS Air Quality Monitor (AQM) uses infrared light and visible light to measure carbon monoxide and visibility in a single compact instrument. The AQM consists of a transceiver that projects infrared beams to a reflector unit mounted 3m away. The reflected light is received by the transceiver and the specific absorption is measured to determine the visibility dimming coefficient and carbon monoxide concentration in the tunnel atmosphere.