Highways Agency - Safe roads, Reliable journeys, Informed travellers

Introduction

Today inductive loops and CCTV are the most common technologies used for detection. New detector technologies are currently being investigated and those which have the potential to be deployed on Agency Roads in the near future are:

• Microwave/Radar
• Infrared Detection
• Magnetic Anomaly Detector
• Fibre Optic Network/Longitudinal Detection

Microwave/Radar

This product has been designed for the detection and monitoring of vehicles at signalled junctions and other applications where the detection of moving targets is required in a long zone extending from the detector.

Their primary use is for detection associated with traffic signals, although they are a potential alternative to inductive loops for other Agency applications such as incident detection.

Infrared Detection

Infrared convert received energy into electrical signals that determine the presence of a vehicle by real time signal processing. There are active and passive infrared detector models which have different detection abilities.

Passive detectors measure the energy emitted by a target or the image of the detection zone.

Infrared detectors emit invisible infrared low-energy by light-emitting diodes to the detector zone and measures the time for reflected energy to return to the detector. A lower return time denotes the presence of a vehicle.

The detectors measure vehicle speed by transmitting two or more beams and recording the times at which the vehicle enters the detection zone of each beam.

Magnetic Anomaly Detector

Magnetic detectors sense vehicles by measuring effects of the vehicles' metallic components on the Earth's magnetic field.

Magnetic detectors can detect volume, speed, presence and occupancy. Their configurations may be single, double, or multiple, depending on monitoring requirements. They generally require multiple detectors per lane due to the narrow focus of the detection field.

Fibre Optic Detectors

Fibre Optic Sensors have no electronic components, which gives them high reliability and immunity to electro-magnetic interference. With the available bandwidth, over 100, sensors can be multiplexed together on a single fibre. Remote interrogation of the sensors is possible from a distance as great as 50 kilometres.

Fibre optic sensors have the potential to measure vehicle dynamics in the road, and early tests of longitudinal sensors (Fibre Optic Longitudinal Detector) have shown they could potentially provide a cost effective alternative to traditional loop and Weigh in Motion (WIM) technologies.