An investigation of comfortable lateral acceleration on horizontal curves

Prior to 2004, design values for side friction factor were based on studies conducted in the 1930's and 1940's. One of the seminal studies collected data from blindfolded passengers being driven around curves. The significance of driving population and passenger car design changes over the last 50 years on horizontal curve design have not been quantified.; The study's objectives were (1) determine the friction factors corresponding to uncomfortable speeds on horizontal curves in a contemporary passenger car; and (2) determine the safety margin against skidding of those friction factors. To meet these objectives, this study intended to duplicate the methodology used in early U.S. roadway experiments---using blindfolded and unrestrained passengers.; The literature review revealed a lack of detail regarding early study experimental design. Therefore the following methodology was used: Male and female subjects of various ages were driven around three horizontal curves at a test track and asked to indicate when they felt "uncomfortable." The curve radii were 318 ft (96.4 m), 454 ft (165.2 m), and 900 ft (272.7 m). Speeds ranged from 35 to 55 mph (56 to 88 km/h). "Uncomfortable" was defined as feeling a sidewards pitch and/or desire to slow down.; The frequency of uncomfortable responses and speed and net lateral acceleration means were examined relative to the values found in the literature. Net lateral acceleration and speed when 10, 50, and 90 percent of the responses would be uncomfortable were interpolated from these data. Safety margins against skidding were determined for the measured values and the 10, 50, and 90 percent uncomfortable calculated values.; Current horizontal curve design standards, though based on older vehicles and passengers, appear to continue to provide a safety margin against skidding that modern passenger car capabilities exceed and lateral accelerations passengers feel are uncomfortable.