Citation

Mclean J. Transp. Res. Rec. 1979; 702: 55-63.

Copyright

(Copyright © 1979, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

While the design speed concept originated from considerations of driver speed behavior, it is now treated as an arbitrary means of designing and matching geometric elements. The implicit assumption of a maximum uniform driving speed is examined in terms of Australian research into the relationships between driver speed behavior and alinement design. For alinements based on design speeds of 110 km/h or more, driver behavior appears to be in accord with the design speed concept. However, for alinements with design speeds between 90 and 110 km/h, driver speeds tend to vary according to the standard of individual features, but the speeds adopted on horizontal curves are generally below the curve design speed. For alinements with design speeds of 90 km/h or less, driver speeds vary along the route and are consistently in excess of the design speed. The results of the speed studies have been used to formulate an alternative approach for the alinement design of two-lane rural roads where topographic or financial difficulties preclude the adoption of design speeds greater than 90 km/h. The method is based on the estimation of a desired speed of travel as related to terrain classification and overall alinement standard. This is used to predict the speed behavior of drivers on individual horizontal curves as a function of the curve standard. This method provides quantification, in terms of driver speed behavior, of what represents a sub-standard curve relative to the overall alinement standard.