Road Weather Management Program
photos of lightning, trucks plowing snow, an empty road before a storm, and an evacuation
Office of Operations 21st century operations using 21st century technologies

Best Practices for Road Weather Management Version 2.0

Best Practices > Publications > Publication Titles

Title:

Synthesis of the Effects of Wet Conditions on Highway Speed and Capacity

Abstract:

Wet and rainy conditions impact the driver, vehicle, and roadway. These effects cause a reduction in speed or density (car-following headway) or both which, in turn, cause a reduction in highway capacity. This paper is a synthesis of 26 studies relating wet conditions to speed and capacity. If the results from all reviewed studies after 1980 with original data from freeways are averaged assuming equal weights, then, the average speed reduction is 4.7 mph in light rain (HCM2000 suggests 6.0 mph which is similar to FHWA's 10 percent reduction) and 19.6 mph in heavy rain (HCM2000 suggests 12.0 mph which is higher than FHWA's 16 percent reduction.) The average capacity reduction is 8.4 percent in light rain and 20.0 percent in heavy rain. The impact of rainy conditions on highway capacity is important. Much additional research is needed for reducing the wide variance of observations in past studies. A methodology is needed for capacity and LOS analysis of freeways, intersections and arterials that accounts for wet conditions as part of typical conditions.

Source(s):

University of Hawaii-Manoa, Department of Civil Engineering

http://www.eng.hawaii.edu/~panos/wet_synthesis.pdf

Date: 2003

Author:

Prevedouros, Kongsil

Keywords:


Capacity
Rain
Pavement condition
Precipitation

PDF files can be viewed with the Acrobat® Reader®.
Office of Operations