A system and method of detecting gases in the exhaust of a moving vehicle with a small engine, such as a motorcycle or moped. The system employs a gas analyzer with a beam which makes more than two passes through a detection space. Through multiple passes through the detection space, the gas analyzer generates a signal indicative of the concentrations of one or more components of interest in the exhaust plume. The system also includes a processor for obtaining information about one or more vehicle exhaust components from the generated signal.