Longitudinal Operational Characteristics of Cars between Small-spacing Interchanges on Freeway

To clarify vehicles'characteristics of longitudinal operation between small-spacing interchanges (SSI) on freeways, a field test with 38 subjects is conducted at Baiyanggou Interchange and Paomaping Interchange in the Chongqing section of the G50 Shanghai-Chongqing Freeway. The onboard instruments collected operational data such as speed and longitudinal acceleration under natural-driving state. Then, the speed range, speed bandwidth, and aggregation coefficient are calculated to analyze the constraints of driving behavior and the characteristics of speed change. Finally, the cumulative frequency, probability distribution, and percentile values are investigated after extracting the peak value of each waveform of the longitudinal acceleration curve. The findings are as follows: In the SSI section, the merging and diverging zones tend to overlap, leading to a great degree of vehicle weaving and interference. Consequently, these areas are marked by a more significant difference of vehicle speed and a heightened degree of dispersion. The cross-sectional velocities typically exhibit a skewed distribution, with the speed range in the SSI being greater than that in other sections. Similarly, the longitudinal acceleration generally displays a skewed distribution, wherein the interval of acceleration negative value exceeds that of positive value. Traffic conditions in the SSI are notably complex, necessitating careful maneuver by drivers. Comparing to the normal-spacing interchanges, the average acceleration decreases by 0.28 m/s² in SSI. In the process of merging, drivers exhibit variability in their preferences for acceleration, with a notable inclination towards higher acceleration positive value (0.542 m/s²) and lower acceleration negative value (－0.081 m/s²). Contrarily, in the process of exiting, drivers demonstrate a certain level of uniformity in their choice of acceleration rates, with minor disparities between the acceleration positive value (0.300 m/s²) and negative value (－0.350 m/s²) rates. Male drivers engage in longitudinal maneuver with a higher frequency than female drivers, albeit at a lower amplitude. Across different driving styles, a certain level of uniformity is observed in the trend of longitudinal acceleration changes.