Impact of Camera and Lighting Position on Video Detection Precision

Abstract

On well-illuminated approaches, vehicle headlight reflections on the pavement were observed to cause video detection units to activate early. This early activation results in a dramatic increase in the length of the effective vehicle detection zone. This observed variation in the effective length of the vehicle detection zone that varies by ambient lighting condition and camera placement presents a very serious impediment for traffic engineers to design vehicle extension intervals that operate correctly during day, night and transition periods. Furthermore, the stochastic variation in the length of the vehicle detection zone length has the potential to create driver expectancy issues. Tables are included that reports the observed average and range of detection zone length variations for 16 observed video cameras that were extensively calibrated by the manufacturer at the test site. The paper concludes by recommending near-side placement of video detection devices to reduce the stochastic variation in detection zone length.