Traffic Detection Systems

Types of Vehicle Detection Systems

Vehicle detection systems are broadly characterized by whether they rely on sensors that require placement within the road surface (known as intrusive systems) or do not require roadway embedment (known as nonintrusive systems).

Intrusive vehicle detection systems in use employ a variety of sensor types, including pneumatic road tube, inductive loop, piezoelectric, bending plate, load cell, capacitance mat, weigh-in-motion (WIM), magnetometer, and magnetic sensor systems, while nonintrusive systems in use include microwave radar, passive and active infrared (or laser radar), ultrasonic, passive acoustic array, and video image processors.

Historically, most vehicle detection systems are infrastructure rather than vehicle based. Pneumatic road tubes record the number of vehicles passing a particular location. Inductive loop detectors are one of the oldest and most common of the vehicle detection systems in use. Various shaped loops of insulated wire are embedded within the pavement, creating a magnetic field that detects passing vehicles. Inductive loop systems range from simple to more complex and may collect data in single or multiple lanes of traffic and from vehicles traveling at varying speeds. They provide data such as vehicle counts, vehicle speeds, vehicle length and weight, and distance between vehicles.

Two-axis floodgate magnetometers obtain vehicle data through measuring vertical and horizontal changes in the Earth's magnetic field. They are primarily used in construction zones, bridge decks, and viaducts where loop detectors are not feasible. Magnetic detection systems utilize a wire coil that measures certain changes in the Earth's magnetic field.

Microwave radar uses the transmission of microwave energy, while active infrared uses the transmission of infrared energy. Two common types of microwave radar in use are continuous wave (CW) Doppler radar and frequency modulated continuous wave (FMCW) radar. Passive infrared systems, which do not transmit energy in themselves, rely on the detection of energy transmitted from passing vehicles, the roadway, and other variables to gather data. Ultrasonic systems measure reflected waves from the transmission of ultrasonic sound energy.

...