Citation

Lam TN, Wasielewski P. Transp. Res. Rec. 1976; 567: 91-97.

Copyright

(Copyright © 1976, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

Spot speed observations were made on a four-lane suburban freeway from November 8, 1973, to June 13, 1974, when speeds were influenced by fuel conservation measures. Speeds were recorded in 15-min intervals in mid-afternoons on 39 days. The mean speed of cars dropped from 63.4 mph (102 km/h) in early November to 60.4 mph (97.2 km/h) in late November to early March and was further reduced to 57.4 mph (92.4 km/h) after the posted speed limit was changed from 70 to 55 mph (113 to 88 km/h) on March 3, 1974. A multiple classification analysis of the 15-min mean speeds showed that the variance of these means was not significantly affected by factors such as time of day, day of the week, traffic flow, and truck composition, although an effect due to different observers was found. The residual variance of the 15-min means after systematic effects were removed was significantly greater than would be expected from sampling errors if the speeds of individual cars were identically distributed. The implications of these results with respect to the planning and design of before and after speed studies are discussed.