Why 'Permissible to Use Tire Chains' Is Not a Chain Law
Date Published
Open almost any state vehicle code, find the section on tire equipment, and you will read that it is permissible to use tire chains of reasonable proportions upon any vehicle when required for safety because of snow, ice or other conditions tending to cause a vehicle to skid.
It reads like a rule about chains. It is not a rule about chains at all.
What the sentence is doing
The surrounding section prohibits anything on a tire that projects beyond the tread — blocks, studs, flanges, cleats, spikes. Chains obviously do project. Without an exemption, running chains would violate the tire-equipment rule.
So the sentence is an exemption carved out of a prohibition. It exists to make chains lawful, not to make them mandatory. Every word of it is permissive.
It appears on both sides of the line
The trap is that the sentence is close to universal. It appears in Arizona, New Mexico, Alaska, Minnesota, West Virginia and Virginia, none of which has a chain law.
It also appears in Idaho, Montana and Wyoming, all three of which do. Finding the sentence tells you nothing either way.
The thing to look for instead
What separates the two groups is a separate provision granting an agency the power to compel. Idaho's section 49-948 continues past the permission into subsections (5) and (6), which let the transportation department establish chain requirements on named passes. Montana's 61-9-406 does the same at subsections (6) and (7). Wyoming's 31-5-956 does it at subsection (e), which lets the superintendent restrict travel to vehicles using chains once signs are erected.
Read for who may compel, not for the word chains. A state that only permits has no chain law no matter how many times the word appears in its code.
Why the error is so persistent
Keyword search rewards the permission and hides the power. The permission uses the obvious search term; the compelling provision is often phrased in terms of restricting travel or requiring traction devices, several subsections away, and sometimes in a different title of the code entirely. A table built by searching for tire chains will systematically overcount.