Stability and mechanism of speed distribution in ultra-narrow vehicle lane traffic flow

Reducing road width can not only save land, but it can also increase traffic safety. However, the traffic flow mechanism due to lane narrowing is not clear and car-following behaviour may also change greatly in this condition. To investigate the influence of lane narrowing, traffic flow data and vehicle trajectory data were collected at a four-lane road section with ultra-narrow lanes during off-peak hours. Statistical analysis of the data revealed that the speed difference between vehicles on an ultra-narrow lane is significantly smaller in unsaturated traffic conditions and the free-flow speed is obviously limited by the lane width, both of which indicate safer traffic flow. Deeper analysis of space speeds and longitudinal gap distances showed that there is a significant correlation between the following distance and the longitudinal gap distance in the adjacent lane, which reveals the special phenomenon that vehicles in different lanes follow the same header vehicle in narrow lanes. In addition, it was also found that the greatest speed difference between the vehicle groups was generally less than 3.5 km/h when staggering occurred. This study provides a theoretical basis for research into car-following theory and decision making while driving in narrow-lane conditions.