Mortimer, R., Hoffmann, E., and Kiefer, A., "The Psychological and Accident Reconstruction “Thresholds” of Drivers' Detection of Relative Velocity," SAE Technical Paper 2014-01-0437, 2014, doi:10.4271/2014-01-0437.
Relative velocity detection thresholds of drivers are one factor that determines their ability to avoid rear-end crashes. Laboratory, simulator and driving studies show that drivers could scale relative velocity when it exceeded the threshold of about 0.003 rad/sec. Studies using accident reconstruction have suggested that the threshold may be about ten times larger. This paper discusses this divergence and suggests reasons for it and concludes that the lower value should be used as a true measure of the psychological threshold for detection of relative velocity.