Citation

Jackson RK, Sessions J. Transp. Res. Rec. 1987; 1106: 112-118.

Copyright

(Copyright © 1987, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

Speeds of loaded logging trucks traveling on single-lane forest roads were studied at three locations in western Oregon to evaluate truck performance on curves and favorable (downhill) grades. Uphill speeds for the returning, empty trucks were also studied. The independent variables of grade, curve radius, width, ditch depth, superelevation, sight distance, time of day, and maximum engine-braking horsepower were regressed against speed. The results were compared with those predicted by the Byrne, Nelson, and Googins (BNG) method and the Vehicle Operating Cost Model (VOCM). Grades above 11 percent strongly influenced speeds; less steep grades only slightly affected speeds. The BNG study and the VOCM predicted downhill speeds reasonably well for straight sections of road with favorable grades between approximately 11 and 16 percent. The BNG method and the VOCM overpredicted speeds for grades steeper than 16 percent. Because of the poor alignment of the roads studied, no conclusions could be reached for favorable grades less than 11 percent. Speeds recorded for curves did not relate to the assumption in the BNG study that horizontal sight distance controls speeds or to the assumption in the VOCM that available friction controls speeds. These findings may influence future road designs. Sight distance may be less important because drivers now use citizens' band radios to learn about road conditions ahead. Technological improvements may also account for differences reported here. Overall, the BNG method underestimated round-trip travel speeds by 16.7 percent when its predicted speeds were compared with those observed over a 7.71-mile portion of a logging road.

Language: en

Keywords

ROADS AND STREETS; HIGHWAY ENGINEERING; FREIGHT HANDLING - Costs