A method of vehicle traffic monitoring based on the detection of characteristic Radio Frequency (RF) emissions. A detector detects RF pulses on multiple frequencies emitted by ignition sparks in a combustion chamber of a motor vehicle within a detection zone. When RF pulses occur on different frequencies simultaneously, the detector increments a count of ignition events within a first pre-defined time window. When the first time window elapses, the detector transmits the count to a central monitoring station. The central station calculates an average change within a second pre-defined time window and updates a running average. When a difference between the count and the running average is greater than a pre-defined congestion threshold, the central station sets a traffic state to “free flowing”. When the difference between the count and the running average is not greater than the pre-defined congestion threshold, the central station sets the traffic state to “congested”.