Today I attempted to get to Idaho Springs, CO from the West in a rented AWD vehicle about 10pm. It was snowing, and my dashboard was showing 23F outside. As I was approaching Vail I saw a number of flashing alerts saying that all AMV (automotive vehicles?) have to fit chains in a designated area where I then saw trucks fitting chains. Cars, however, were just proceeding straight through. I did not have any chains, and because I had been in the US for only 4 days (for the first time!) I decided to turn back, stay the night safe and decide what to do tomorrow.

I have now found that alert on cotrip.org:

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The alert is saying that AWD vehicles are OK to drive there. However, my assumption is that assumes winter tires.

Could somebody please clarify from their knowledge/experience of driving that road:

  1. Are AWD vehicles required to fit chains when that kind of alert is on? If no, are they required to have winter tires fitted?
  2. If winter tires are required, will M+S (mud + snow?) tires fit the definition of "winter tires" in this case, or do they need to be studded?
  3. How steep/dangerous the road is in terms of the risk of losing traction?
  4. Given that the rental company is aware of the pickup/dropoff locations (Las Vegas -> Denver), would it be normal/lawful for them to apply penalties if I cannot drop the car off in the agreed place/time (Denver tomorrow morning) because I am not allowed to drive the car because it does not satisfy the requirements of the Traction Law Alert? If I cannot drive there my intention would be to call them and arrange alternative dropoff location.

If you can answer any of the questions above please do! Thanks!

P. S. I noted this closely related question but it does not address what I am asking.


I just noted there is now another alert called CHAIN LAW which explicitly requires ALL vehicles to have chains (apparently, the flashing screen I saw on the road was conveying this alert, not the Traction Law one):

enter image description here

  • 1
    In the case of the second alert, it applies to CMVs: commercial motor vehicles. They are intended to cover buses and trucks, but a rental car would probably be included as well.
    – jcaron
    Commented Mar 6, 2018 at 13:13

1 Answer 1


Just found answers to questions 1 and 2:

Traction Law (Code 15)

During an active Traction Law (also known as a Code 15), motorists must have either snow tires, tires with the mud/snow (M+S) designation, or a four-wheel/all-wheel drive vehicle. All tires must have a minimum one-eighth inch tread.

Under a Traction Law, both metal-studded and studless snow tires comply with the "snow tire" requirement of the law. CDOT recommends using studless snow tires instead of studded because studded tires can chip and cut grooves in the road, creating a hydroplaning hazard when the roadway is wet. Whether using studded or studless snow tires, all the tires must have a minimum one-eighth inch tread.

So, if it was the Traction Law alert only (not Chain Law Alert) then an AWD would be fine even with non-winter tires. But there was also a Chain Law Alert which requires ALL vehicles to have chains fitted:

Under an active Passenger Vehicle Chain Law, every passenger vehicle will need to have chains or an alternative traction device equipped.

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