Citation

Yagar S, Van Aerde M. Transp. Res. A Gen. 1983; 17(4): 315-325.

Copyright

(Copyright © 1983, Elsevier Publishing)

DOI

10.1016/0191-2607(83)90094-8

PMID

unavailable

Abstract

A study of the effects of various geometric and environmental factors on the speeds for 2-lane rural highways was performed in Ontario, Canada using 1980 data which had been collected by means of the Radar-Platoon technique. Over 5000 5-min periods of data, collected at 35 different locations, were used to estimate the effects of the various contributing local factors. Each of these contributing factors was formulated as the exponentially smoothed average of the geometric properties up to 1500 m upstream. To control for varying traffic volumes, the speeds used for estimating the geometric effects were those corresponding to main direction volumes of 900 passenger car units (pcu) per hour and opposing volumes of about 300 pcu/hr. A multiple linear regression model related measured speeds to the upstream influencing properties of the highway. Land use adjacent to the road, and legal speed limit, were found to have the most significant impacts on speed. Grade, access from other roads, and lane width, followed in that order. The above significant factors explained 85% of the across-sites variation in speed, leaving relatively small residual errors. Road curvature, presence of an extra lane, sight distance, center line markings and lateral obstructions were not found to have statistically significant effects on speed. Stronger statistical relationships could be obtained for both the above significant and insignificant factors, by testing these factors over wider ranges than those available on Ontario's highways, as Ontario uses relatively high and uniform design standards. For example, gradients were limited to less than 3%, and radius of curvature to greater than 1400 m.