Track Curvature Characteristics and Vehicle Cornering Patterns on Hairpin Curves

To clarify the vehicle trajectory characteristics and driving behavior preference of hairpin curves of mountain roads, the vehicle trajectory and lateral distance between wheel track and lane marking on hairpin curves were collected in the condition of natural driving, the track curvature were calculated with the measured track data, the relationship between the track curvature and road design curvature were analyzed, and the changing mode of the track curvature was determined. Moreover, the concept of track equivalent radius was presented, and the cornering behavior and typical track patterns on hairpin curves were analyzed. It is found that 1) serious lateral deviation can be observed at entrance, middle and exit of a hairpin curve. 2) At the entrance of a hairpin curve, the vehicle has begun the state of curve driving before running on the transition section, and at the exit, the track curvature reduces to zero on a tangent after departing the transition section; the change rate of track curvature is lower than that of the transition. Gradient of the left-turn track is lower than that of the right-turn track. 3) The curvature of the left-turn track at the middle of the hairpin curve is lower than or close to the design curvature, while the curvature of the right-turn track is higher than the design curvature. 4) The equivalent radius of left-turn track is higher than the design radius of the hairpin curve, while the minimum and average equivalent radius of the right-turn track are generally lower than the design radius. 5) Drivers can increase and maximize the track radius with different cornering behaviors, but need to drive on the opposite lane. 6) When a driver cuts a corner, the increment in track radius of the left-turn curve is higher than that of the right-turn curve; namely, it is easier for a vehicle to turn left into the hairpin curve to cut a corner; of three types of hairpin curves, big, flat and small curves, which correspond to the deflection angles larger than 180°, equal to 180°, and less than 180°, the curves with the deflection angles larger and less than 180° lead to better vehicle cornering performance.