Car-following characteristics and speed model of highway tunnel vehicles

To investigate the relationship between car-following behavior and following speed on expressway tunnel sections, and to develop quantitative models linking space headway, time headway, and relative speed to following speed. Naturalistic driving experiments were conducted on real expressways with normal traffic flow across multiple tunnel sections. Following speed, space headway, time headway, and relative speed were collected, their relationships with following speed were modeled, and the influence of the leading vehicle type was further analyzed. The fitted models exhibited high goodness-of-fit (R2 = 0.86, 0.94, 0.76, 0.80, 0.55, and 0.77, respectively). In the primary speed range, space headway increased with speed and relative speed declined gradually, whereas time headway gradually decreased when following a car but first increased and then decreased when following a large vehicle. When the leading vehicle was large, space headway grew faster and the speed difference rose more markedly than when following a car. These findings reveal the nonlinear nature of car-following behavior in expressway tunnels and confirm the moderating role of the leading vehicle type, providing a reference for calibrating car-following algorithms in tunnel environments.