California Department of Transportation
Caltrans > District 2 - Northeastern California > Chain Control > Chain Control Requirements Defined

District 2 - Northeastern California Chain Control

Chain Control Legend Metering Traffic - Implemented when necessary to control the number of vehicles that feed into the snow area. This congestion control procedure gives Caltrans a better chance of keeping the freeway open. Vehicle Screening - All vehicles will be checked to make sure they have a full set of tire chains before being allowed to travel into areas where chains will be required. Truck Screening - All semi-trucks will be checked to make sure they have a full set of tire chains before being allowed to travel into areas where chains will be required. No Restrictions - Watch for snow on pavement. Chains are required on single-axle drive vehicles with trailers. (commonly referred to as R1 Modified) Chains are required on all commercial vehicles (trucks or buses). All other vehicles (cars, pick-ups, vans, etc.) must have either snow tread tires or chains on the drive axle. Chains are required on all vehicles except four-wheel drives with snow tread tires on all four wheels and provided that tire traction devices for at least one set of drive wheels are carried in or upon the vehicle. Chains required - ALL VEHICLES- no exceptions. Road Closed. Truck Hold - During major storms when traffic flow is heavy, Caltrans may hold tractor-trailer combinations at specific points below the snow line.

CHAIN CONTROL REQUIREMENT LEVELS
W: No Restrictions - Watch for snow on pavement.
R-1M: Chains are required on single-axle drive vehicles with trailers (commonly referred to as R1 Modified)
R-1:
Chains are required on all commercial vehicles (trucks or buses). All other vehicles (cars, pick-ups, vans, etc.) must have either snow tread tires or chains on the drive axle.
R-2:
Chains are required on all vehicles except four-wheel drives with snow tread tires on all four wheels and provided that tire traction devices for at least one set of drive wheels are carried in or upon the vehicle.
R-3: Chains required - ALL VEHICLES- no exceptions
C: Road Closed
T:
Truck Hold - During major storms when traffic flow is heavy, Caltrans may hold tractor-trailer combinations at specific points below the snow line.
TS:
Truck Screening - All semi-trucks will be checked to make sure they have a full set of tire chains before being allowed to travel into areas where chains will be required.
VS:
Vehicle Screening - All vehicles will be checked to make sure they have a full set of tire chains before being allowed to travel into areas where chains will be required.
MT:
Metering Traffic - Implemented when necessary to control the number of vehicles that feed into the snow area. This congestion control procedure gives Caltrans a better chance of keeping the freeway open.

R-1 and R-2 are the most common chain controls. The highway will often be closed before an R-3 control is imposed.