Idaho's Chain Law Covers Three Mountain Passes and Nothing Else
Date Published
Idaho has the narrowest chain law of any state that has one. It reaches three named crossings and stops there.
The three passes
Idaho Code 49-948 subsection (5) lets the Idaho Transportation Department establish chain requirements for commercial vehicles on Lookout Pass and Fourth of July Pass on Interstate 90, and Lolo Pass on State Highway 12. Those three are the whole of it. There is no general power to require chains on any other Idaho highway.
The trigger is a determination by the department that the pass is in an unsafe condition such that chains are required.
What the department has to do first
The statute constrains the department more tightly than most chain laws constrain theirs. Before a requirement binds, the department must provide multiple advance notices, provide adequate opportunities to pull out, and give notice at a point at which a commercial vehicle can safely pull out of the normal flow of traffic before reaching the point where chains are required.
Subsection (5)(d) is unusually direct: in no case may the department post requirements for chains on bare pavement.
That clause protects drivers. It prevents a requirement being left standing after a pass has cleared, which is the situation in which chaining does more harm than good.
What satisfies the requirement
Under subsection (6), the requirement is met by chaining one tire on each side of one drive axle, regardless of how many drive axles the vehicle has, plus one axle at or near the rear of each towed vehicle. That rear axle may not be a variable-load suspension axle or an axle of a converter dolly.
Subsection (7) allows any other traction device differing from chains in construction, material or design but capable of providing traction equal to or exceeding that of chains under similar conditions.
Who is exempt
Subsection (9) exempts motor vehicles operated by the transportation department when used in maintaining the interstate or state highway system, and vehicles employed solely in transporting school children and teachers.
The wider point about Idaho
Idaho is one of three states where the chain power sits in the vehicle code rather than in an administrative rule. Montana and Wyoming are the others. Anyone searching only IDAPA, the state administrative code, will conclude Idaho has no chain law at all. It has one. It is written somewhere else, and it is very small.