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Table 9 Difference between the average speed in different light conditions (darkness, twilight) and the average speed in daylight for the same road, month, and weather condition (clear, rain, snow)

From: Effects of weather conditions, light conditions, and road lighting on vehicle speed

Weather Light cond. Road lighting Speed − speed in daylight
Clear Darkness No lighting 1.0
Rain Darkness No lighting −0.9
Snow Darkness No lighting −3.5
Clear Twilight No lighting 1.2
Rain Twilight No lighting −0.2
Snow Twilight No lighting −1.2
Clear Darkness Lighting 1.1
Rain Darkness Lighting 0.6
Snow Darkness Lighting 0.2
Clear Twilight Lighting 0.8
Rain Twilight Lighting 0.4
Snow Twilight Lighting −0.3
  1. Difference in km/h. Differences are shown for different weather conditions and for roads with/without road lighting