Mountain pass conditions are changing all the time, from snow to ice to slush, and that can create very difficult driving conditions.
Crews constantly monitor the changing conditions throughout the winter months and post advisories on the pass Web sites and on signs on the highways to let you know how safe the passes are to cross. They have been busy lately, but that's another story.
The three advisories we use are:
- Traction tires advised
Oversize loads prohibited. Oversize vehicles may be restricted from roadways during severe weather conditions.
- Traction tires required
Passenger vehicles must use approved traction tires. Chains are required on all vehicles over 10,000 gross vehicle weight rating (GVWR), including large passenger trucks and SUV's over 10,000 GVWR.
- Tire chains required
Chains required on all vehicles - except four/all wheel drive. In extreme weather conditions, the advisory may indicate chains are required on all wheel drive vehicles.
Traction tires must be labeled with a M+S rating (mud and snow), be an all season tire, or have a mountain snowflake symbol on it.
Types of traction tires:
- Stud alternative
This stud-less tire has over 3,200 sipes to help grip the winter roadway. The soft rubber compound helps during wet weather conditions, but is too soft for warmer, summer driving.
This studded tire has staggered studs designed to wear with the tire. While providing additional traction on snow and ice, studs wear down the roadway and are only permitted November 1 through March 31.
- All season
This all season tire is designed for everyday driving. The rubber compound is suitable for all weather conditions. Siping (small slots cut or molded into a tire tread surface) greatly increase this tire's traction on winter roadways.
Interesting that Wikipedia states this tire is "neither an excellent summer tire nor an excellent winter tire" and "have become almost ubiquitous as original and replacement equipment...due to their convenience and their adequate performance in most situations." Hope that helps explain what a traction tire is.
The state patrol also has some great information on their Web site and even links to the WAC 204-24-040 that defines the law for traction devices if you are so inclined.