In the video detection system of urban traffic flow

it is a hard work to detect vehicle at night. The traditional methods are based on vehicle headlights and headlight beams using mathematical morphology

they are sensitive to environment illumination with high computing cost. This paper presents a method based on color and motion information. Firstly

the algorithm detects and tracks vehicle taillights using color information on the images

then matches the detected vehicle taillights using motion information and priori knowledge

finally vehicle flow is computed. As shown in experiments

the algorithm can exactly detect moving vehicles at night and it is robust to rainy conditions.