With winter weather already affecting Colorado’s mountain highways, the Colorado Department of Transportation (CDOT) is reminding commercial motor vehicle (CMV) drivers that the state’s chain season has begun. The agency is emphasizing the importance of preparation to ensure safety on the roads.
The updated chain law, known as the “Must Carry Law,” entered its second year after being signed by Governor Jared Polis in 2024. The regulation requires all CMV drivers to carry tire chains from September 1 to May 31 each year. This rule applies to vehicles with a combined weight exceeding 16,000 pounds that are used in commerce or for transporting at least 16 passengers, including the driver, on public highways.
Drivers who fail to comply with this requirement may face fines: $500 for not carrying chains and up to $1,000 plus a surcharge if their vehicle blocks the roadway. CDOT provides detailed information about the law and lists chain-up stations across Colorado on its website.
A map showing where CMVs must carry chains or alternative traction devices—regardless of current weather conditions—includes stretches of I-70 and several state highways such as Highway 9 and US Routes 40, 50, 160, 285, and 550. Fact sheets are available for download through CDOT’s Freight Mobility website.
Colorado’s mountain roads present particular challenges due to steep grades, unpredictable weather patterns, and frequent heavy snow. Commercial vehicles and buses have a larger presence on these routes where chains are required. Vehicles lacking proper traction can cause road closures that disrupt transportation of goods and people throughout the state.
Preparation for winter driving includes checking weather forecasts before starting routes and ensuring that chains are accessible in vehicles. When storms occur, drivers often use chain-up stations along highways—sometimes at night or in freezing temperatures—to install their chains before continuing over steep terrain at reduced speeds. After crossing affected areas, they stop again to remove the chains. These procedures add complexity to their work alongside federally mandated rest periods and long hours.
According to CDOT: “Their efforts keep Colorado’s roads open, freight moving and mountain communities connected, even during the harshest storms.”
