Perceptual Thresholds in Car-Following—A Comparison of Recent Measurements with Earlier Results

The authors have previously conducted a field experiment to investigate the sensitivity of subjects to the sign of relative motion when following a vehicle. They interpreted their results in terms of responses to analytical functions of relative speed divided by spacing, or spacing change divided by spacing. In the present paper the remits of a number of other field, simulator, and laboratory experiments to investigate sensitivity to relative motion reported in the literature are examined in the light of these analytical response functions. It is shown that this approach leads to a relatively consistent interpretation of most of the available data, and that, when appropriately interpreted, there is greater agreement between many of the experimental results than had hitherto been noted.