A vehicular reference instrument for field verification of traffic speed meters based on laser Doppler velocimeter

A new vehicular reference instrument based on laser Doppler velocimeter with dual-beam (dual-beam LDV-VRI) is proposed for field verification on the fixed traffic speed meters in all road surfaces and all road conditions in this paper. The dual-beam LDV-VRI measures the moving speed based on the Doppler effect and calculates the driving distance by the moving speed integral over time, and it can provide the reference speed and the reference distance with high accuracy by use of dual laser beams to correct the beam pointing angle error. A principle prototype is realized with speed ranged (1–200) km/h with measurement MPE ±0.10 km/h (<100 km/h) or ±0.10 % (≥100 km/h) and distance ranged (0–400) km with measurement MPE ±0.10 %. The field comparison experimental results validate that the dual-beam LDV-VRI is effective and reliable for measuring the reference speed and the reference distance of the test vehicle.