Empirical Studies on Traffic Flow in Inclement Weather
Figure 5.8. This figure presents four plots of Free-flow speed weather adjustment factor (WAF), speed-at-capacity WAF, capacity WAF and density-at-capacity WAF, versus precipitation intensity for both rain and snow. WAF at zero precipitation intensity is 1.00. Rain free-flow speed WAF rapidly decreases to 0.98 in the presence of precipitation and then linearly decreases to 0.94 as precipitation intensity increases to 1.6 centimeters per hour and snow free-flow speed WAF rapidly decreases to 0.90 in the presence of precipitation and then gradually decreases to 0.85 as the precipitation intensity increases to 0.35 centimeters per hour. Rain speed-at-capacity WAF rapidly decreases to 0.96 in the presence of precipitation and then linearly decreases to 0.92 as precipitation intensity increases to 1.6 centimeters per hour and snow speed-at-capacity WAF rapidly decreases to 0.90 in the presence of precipitation and then gradually decreases to 0.85 as the precipitation intensity increases to 0.35 centimeters per hour. Rain capacity WAF rapidly decreases to 0.89 in the presence of precipitation and stays constant as precipitation intensity increases to 1.6 centimeters per hour and snow free-flow speed WAF rapidly decreases to 0.80 in the presence of precipitation and stays constant as the precipitation intensity increases to 0.35 centimeters per hour. Rain density-at-capacity WAF rapidly decreases to 0.93 in the presence of precipitation and then linearly increases to 0.97 as precipitation intensity increases to 1.6 centimeters per hour and snow density-at-capacity WAF rapidly decreases to 0.88 in the presence of precipitation and then gradually increases to 0.94 as the precipitation intensity increases to 0.35 centimeters per hour.
