Characterization of Longitudinal Acceleration at Curves in Urban Underground Ring Roads

To improve the safety at the curve of underground roads, the characteristics of velocity and acceleration of six curves were analyzed. The results show the following: (1) The radius of the curve is positively correlated with the mean value of acceleration and deceleration and the frequency difference. (2) The speed change in a single curve and curve with the same radius first reduces and then increases, while in the curve with inconsistent radius, the speed change decreases greatly and increases, then decreases slightly and increases. (3) Except for C3 (R = 30 m), there is a speed center point. When the speed is less than the point, acceleration and deceleration increase monotonically with the speed and decrease monotonically when it is greater than the absolute value of deceleration, which is consistent with the conclusion of acceleration. This study would be helpful to improve the safety of underground ring road curves.