Idaho Studded Tires: Banned May 1 to September 30

The controlling text is Idaho Code section 49-948, "Restrictions as to tire equipment," in chapter 9 of title 49 (vehicle equipment). Subsection (3) starts from a general ban on any block, stud, flange, cleat, spike or other protuberance of a material other than rubber projecting beyond the tread, then carves studs back out: tires with built-in lugs of tungsten carbide or other suitable material "may be used upon any vehicle when required for safety because of snow, ice, or other conditions tending to cause a vehicle to skid, that will not unduly damage the highway." Two conditions ride on that permission that Idaho drivers routinely overlook. The permission is conditional on winter conditions and on the studs not unduly damaging the pavement, so it is not an unqualified right to run studs on bare October asphalt, and the same subsection expressly preserves the right to use tire chains, which are the alternative Idaho pushes on its mountain passes.

The seasonal bar is worded as a prohibition, not as a permission: studded vehicles "are prohibited on public highways between the dates of May 1 and September 30, annually." That phrasing matters because it means the legal window is defined by subtraction. There is no separate sentence granting an October-to-April season, and there is no provision letting the department stretch a late spring by a week. The Idaho Transportation Department states the same window publicly as October 1 through April 30, and describes running studs outside it as a non-moving equipment violation.

Idaho once had an administrative rule on this subject, IDAPA 39.03.46, "Rules Governing Studded Tires," published by the Transportation Department in the 1999 and 2000 editions of the Idaho Administrative Code. It is no longer part of the current code: the current-rules directory for agency 39 serves other Transportation Department chapters and returns nothing for 39.03.46, and the chapter had already dropped out by the 2004 edition. Idaho therefore has exactly one instrument on studded tires, and it is the statute.

Three exceptions are written into section 49-948(3). Paragraph (a) exempts fire pumper/tanker trucks and ladder trucks belonging to fire departments and firefighting agencies from the prohibited dates outright. Paragraph (b) allows a vehicle to be equipped year-round with retractable studs, provided the studs retract pneumatically or mechanically to at or below the wear bar when not in use and protrude beyond the wear bar only between October 1 and April 30; retractable studs may be metal and are exempt from the stud weight limits in subsection (4). Paragraph (c) lets the Idaho transportation board grant special exemptions from the prohibited dates where the board finds that enhancements to public safety outweigh the increased pavement wear. That is the only delegation in the section, and it reaches individual exemptions, not the dates themselves.

Subsection (4) regulates the hardware rather than the season, and it binds sellers and installers rather than drivers. Since July 1, 2005 commercial tire retailers may not sell studded tires, and retailers and tire shops may not manually install studs, exceeding stated limits: studs may not protrude more than six-hundredths (.06) of an inch from the tread surface when originally installed, stud size must be as recommended by the tire manufacturer for the type and size of tire, and individual stud weight is capped at 1.5 grams for size 14 or smaller, 2.3 grams for size 15 or 16, and 3 grams for size 17 or larger.

Subsections (5) through (9) of the same section deal with the related winter question of chains. If the department determines that Lookout Pass or Fourth of July Pass on Interstate 90, or Lolo Pass on State Highway 12, is unsafe, it may require chains on commercial vehicles travelling those routes, but only after providing multiple advance notices, adequate pull-out opportunities, and notification at a point where a commercial vehicle can safely leave the traffic flow, and it may never post a chain requirement on bare pavement. Chaining means one tire on each side of one drive axle plus one axle at or near the rear of each towed vehicle. School buses operated by a school, farm vehicles carrying the farmer's own equipment or supplies, agricultural hauls, mail carriers, forest-product and mine-product carriers, and wrecker or tow trucks are exempt from those chain requirements.

Section 49-948 sits in chapter 9 of title 49, and Idaho Code section 49-236(2) makes a violation of chapters 3, 4 and 6 through 9 of that title an infraction rather than a misdemeanour, unless a section says otherwise. Section 49-948 says otherwise nowhere, so running studs in June is an infraction and cannot carry jail. Idaho State Police and city and county officers enforce it roadside; Idaho has no periodic safety inspection lane in which studs would be caught. 50 before the statutory fees and surcharges are added.

The Idaho Transportation Department has publicised the all-in figure as $67. A driver who wants to contest it appears in the magistrate division of the district court in the county of the citation; an infraction judgment carries no right to a jury and no possibility of a withheld judgment or suspended penalty under Rule 9. The subsection (4) limits on stud protrusion and weight are enforced against the retailer or tire shop that sold or installed the studs, not against the motorist who bought them.