Modern ball-banking limiting values

Abstract

In 1940 R. A. Moyer and D. S. Berry established ball-banking limiting values (and side friction factors) for use in determining the maximum recommended speed of horizontal curves on roads (the value shown on advisory speed plates). This speed is also referred to as the "advisory speed", "safe speed", or the "comfortable speed" of the curve. This speed is distinguished from the "critical curve speed", the speed value at which loss of control is imminent. Literature review showed some concern for the criteria for the installation of curve warning signs but no recent concern for the goodness of the limiting values. Ritchie et. al. has provided updated research on lateral acceleration values. Their research, plus results of this study, show that the 1940 values are outdated. This work concludes with recommended modern ball-banking limiting values, side friction factors, and lateral acceleration values. Recommendations regarding further research are stated.