Montana Studded Tires: October 1 to May 31, and MDT Cannot Shorten It

The Montana rule is written as a prohibition with a seasonal exception carved out of it. Section 61-9-406(3) says a tire moved on a highway may not carry on its periphery a block, stud, flange, cleat, spike or other protuberance of a material other than rubber that projects beyond the tread. The escape hatch is in the same paragraph: tire chains of reasonable proportions are always permissible, and so are pneumatic tires whose traction surfaces have been embedded with wood, wire, plastic or metal, provided the embedded material does not protrude more than one-sixteenth of an inch beyond the tire tread. The statute treats a sidewall marked by the manufacturer "all season m&s" or "all season mud and snow" as satisfying the same paragraph, which is why an ordinary M+S winter tire carries no seasonal limit at all in Montana.

The season is the part most drivers get wrong. Embedded studs are permitted only between October 1 and May 31 of each year. One studded tire may be carried as a spare outside that window in case of tire failure, which is an express allowance rather than a tolerated practice. School buses fitted with embedded pneumatic tires get a materially longer season, August 15 through the following June 15, reflecting the fact that Montana districts start running routes over passes in late summer.

Subsection (4) handles retractable studs separately and more generously. A pneumatic tire with a retractable block, stud, flange, cleat, spike or other protuberance may be used at any time of the year. The catch is the second sentence: outside October 1 to May 31, the protuberance may not be engaged or extended on roads that do not contain ice or snow. So a Montana driver with a retractable system may legally leave the tires mounted in July and deploy the studs on an icy August morning over Homestake Pass, which a driver on fixed studs may not.

The Montana Department of Transportation has power to add to these requirements but not to subtract from them. Under subsection (6) MDT may determine at any time that dangerous or unsafe conditions on a highway require particular tires, tire chains or traction devices beyond ordinary pneumatic rubber tires, and subsection (7) requires it to place and maintain signs and traffic control devices announcing that determination. Subsection (7) then limits the agency in plain words: those signs may not prohibit the use of embedded pneumatic tires between October 1 and May 31. When MDT decides chains are required and no other traction device will suffice, the requirement reaches tires on the driver wheels of one axle, as axle is defined in 61-10-104, including embedded tires, and the signs may set different requirements for four-wheel-drive vehicles in gear.

A separate 2023 statute, § 61-9-436, adds a carriage duty for heavy trucks. From October 1 through April 30, a person operating a motor truck of 26,001 GVW or greater towing a trailer on a mountain pass or a similar stretch of highway that MDT has designated as a place where traction control devices are potentially required must carry approved traction control devices prescribed by the department. Four-wheel-drive vehicles are exempt. Note the two different end dates: the studded-tire season closes May 31, the truck carriage duty on April 30.

The two halves of § 61-9-406 carry very different penalties. Ignoring an MDT chain or traction-device sign posted under subsections (6) and (7) is prosecuted under § 61-9-520 as the nonmoving offense of failure to use chains or approved traction devices when required, and the fine is fixed: $250, or $750 where the violation results in an incident that closes all lanes in one or both directions of a highway. Section 61-9-520(2) states that this violation is not a misdemeanor subject to 45-2-101, 61-9-511 or 61-9-512, so it does not carry the general criminal exposure attached to the rest of the equipment chapter.

Running fixed studs outside the October 1 to May 31 window is different: no special penalty is provided, so it falls to the residual scale in § 61-9-511(2), a fine of $10 to $100 on a first conviction, $25 to $200 on a second conviction within one year, and $50 to $500 on a third or subsequent conviction within one year of the first. Failing to carry traction devices under § 61-9-436 draws $225 for a first offense and not less than $225 or more than $500 for subsequent offenses. Enforcement is roadside by the Montana Highway Patrol and local peace officers; Montana has no periodic safety inspection at which tires would be checked.