Field Measurement of Automobiles’ Lateral Accelerations

To provide design basis for alignment parameters of different types of highways, the lateral accelerations, speeds, and trajectory curvature radii of passenger cars and buses on 12 highways having different design speed and topography were collected in field survey. The level of driving comfort on each test roads was estimated according to vehicle lateral acceleration. The characteristic percentile value of lateral acceleration on three road types, i.e., six-lane road, four-lane road and double-lane road, were presented. For passenger cars and buses on the three kinds of roads, regression models between lateral acceleration and trajectory radii, and between lateral acceleration and speed were established, including the average value model, the extremum value model, and the 85th percentile value model. The results show the following findings: (1) driving comfort becomes poor as lane numbers decreases. For two-lane highways with a design speed of less than 30km/h, the uncomfortable travel on partial section is unbearable. (2) The inflection point on cumulative probability curve of lateral acceleration appears at the 90-92th percentile, and the maximum value on two-lane highways exceeds 8 m/s2. (3) The distribution of lateral acceleration tends to assemble as the trajectory curvature decreases or the lane number increases, and lateral acceleration distribution of buses is more centralized than the ones of passenger cars. (4) The extremum value model between lateral acceleration and trajectory radii and the 85th percentile value model between lateral acceleration and speed can provide design control for the maximum/minimum value of road geometry elements, and the average value models can control the general value of road geometry elements.