Top Hazards for Commercial Motor Vehicles in Adverse Driving Conditions

The Federal Motor Carrier Safety Administration found that 25% of speed-related large-truck fatalities occurred during adverse weather conditions.

Published November 6, 2018

By Ricky L. Nguyen, M.S., P.E.

With the winter season approaching, hazards increase for drivers involved in driving in adverse driving conditions (such as in snow and ice), especially for commercial motor vehicles (“CMVs”). Vehicle speed and tire traction affect the safety of these vehicles in these conditions.



Since adverse conditions influence road conditions and visibility, higher vehicle speed may cause more severe and sometimes fatal crashes. The Federal Motor Carrier Safety Administration (“FMCSA”), the government enforcement agency in the motor carrier industry, found that 25% of speed-related large-truck fatalities occurred during adverse weather conditions.   The FMCSA recommends CMV drivers reduce their speed by one-third on wet roads and by one-half on snow packed roads (i.e. reduce speed from 60 mph to 40 mph on wet roads, 30 mph on snow packed roads).  The reduction of speed can not only reduce the severity of crashes, but it can give the driver more time and distance to react in hazardous situations.

Available traction on tires affect the safety of CMVs in adverse weather conditions.  Sufficient tire tread depth allows snow to escape through the valley in between the treads and allows sufficient tire material to “bite” onto the road surface.  Insufficient tire tread depth can allow snow to cake onto the tire and reduce the traction of tires, reducing the vehicles’ acceleration, braking, and steering ability.

The national regulations & most states require minimums of 4/32 of an inch tread depth for steer tires and 2/32 of an inch for other tires.  Tire distributors and tire testing recommend a minimum of 4/32 of an inch tread depth on all tires when driving over snow-packed or icy road conditions.  States that are more prone to adverse weather conditions, such as Colorado, have chain laws that require CMVs to have tires with tread depth above the national regulations.  Furthermore, if the vehicle does not meet the tread depth minimum during the chain law restriction, the vehicles has to have chains or alternative traction devices on the tires.  It should be noted that not all jurisdictions within the state has a chain law restriction, but law enforcement does tend to follow nearby restrictions.

Knott Laboratory assesses and analyzes many accidents involving CMVs in adverse driving conditions. Consider Knott Laboratory in analyzing your next case.