Automobiles on Horizontal Curves: Experiments and Observations

Statistical information on the basic variables involved in driving through a horizontal curve was obtained using a 4×4 Latin square design experiment to measure the action of automobile drivers in test track horizontal curves. The independent variables used in the test curves were speed (comfortable, fast); pavement surface (dry, wet); driver (male, female); and curve radius (16 m, 26 m, 60 m, 100 m). The measured output was the driver’s selected speed and corresponding lateral acceleration. In addition, the passengers indicated their comfort level on a four-point semantic scale. Expert drivers also drove the test curves to establish the upper limits of the driver-vehicle-tire system. Field observations of four curves along a two-lane rural mountain highway measured driver vehicle speed, lateral acceleration, and lateral position. The results indicate that, for a comfortable ride, drivers are limited by their comfortable lateral acceleration on small radius curves and seek the “environmental speed” on large radius curves.