Citation

Dean JP. Transp. Res. Rec. 1977; 624: 129-135.

Copyright

(Copyright © 1977, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

Wet accident experience of rural highway sections in New Brunswick, Saskatchewan, Ontario and Kentucky was related to measurements of average wet pavement skid resistance, SN sub 40, in separate and combined analyses. Two classes of highway were analysed: two lane unidivided rural arterials having posted speeds 96-104 km/hr (60-65 mph), and average annual traffic volumes 0-8400 vpd; two lane divided rural freeways and parkways having posted speeds 112 km/hr (70 mph), and average annual traffic volumes 1100-34000 vpd. The data exhibited strong nonlinear variation and considerable scatter. Ten point moving average plots of wet accident experience vs SN sub 40 served to subdude scatter and identify SN sub 40 levels at which significant increases in wet pavement accident experience occurred. Plots of wet accidents per mile vs SN sub 40 appeared to have less scatter than those in which the significant relative frequency of wet accidents was used as the wet accident variable. In addition, wet accident experience averaged over 2 or more years gave less scatter than plots of yearly wet accident experience. Preliminary equations were developed from the data using a non-linear least squares computer program. Two lane undivided rural highway data exhibit a higher level of wet pavement skid resistance demand than that for four lane divided rural highways. Wet pavement skid resistance ranges at which marked increases in wet accident experience occurred were, for two land rural arterials: SN sub 40 = 55-60; for four lane rural freeways and parkways: SN sub 40 = 43-50. Present recommended minimum wet pavement skid resistance levels for highways having mean speeds in the range of 64-112 km/hr (40-70 mph), appear to be low when the trends of this study are examined.