A Guide to Braking to a Stop on Varying Road Surfaces.
These values are for guidance only and are based on average skid distance. The skid distances presented do not account for speed losses from impacts or other events at any point in the skid. There is also no account taken of partial braking, an inefficient braking system or braking on one wheel for instance by a motorcycle.
The value ranges are ostensible and may not apply to any specific situation. Accurate drag factor values are best determined by on-site testing.
Please note these tables only show braking distance and do not take into account driver reaction time / distance which will increase the overall stopping distance of a vehicle. Please refer to graphs for average reaction times.
Guide to the ranges of drag factors for different types of road surfaces:
Concrete, new, sharp, dry - 0.70 to 1.10
Concrete, travelled, dry - 0.60 to 0.80
Asphalt, new, sharp, dry - 0.70 to 1.10
Asphalt, travelled, dry - 0.60 to 0.80
Concrete, new, sharp, wet - 0.60 to 0.80
Concrete, travelled, wet - 0.50 to 0.80
Asphalt, new, sharp, wet - 0.60 to 0.80
Asphalt, travelled, wet - 0.50 to 0.80
Gravel, loose, dry - 0.40 to 0.70
Snow, packed - 0.30 to 0.55
Snow, loose - 0.10 to 0.25
Ice, smooth - 0.10 to 0.25
Note: The grip of a road surface can be reduced when greasy, muddy etc.