Fibre-optic axle sensors for vehicle data collection

Axle sensors are extensively used in traffic counting and classification systems. Most modern axle sensors are constructed of piezoelectric plastics. These give good all round performance and, coupled with charge amplifiers, offer reasonable sensitivity and low speed performance. Fibre-optic materials are now being investigated for two principal reasons. First, as piezoelectricity is generated by mechanical impulses, such sensors do not respond to static loads. Unfortunately, as congestion increases (and sites of traffic interest are often those where congestion occurs), stationary or very slowly moving vehicles are increasingly common. Fibre-optic sensors offer static as well as dynamic measurement. Secondly, a replaceable `Tee´ section piezoelectric sensor costs over £150, and fibre-optic technology, because of its wide use in the communications industry, has the potential to become the basis of cheaper sensors