Dan,
The funny thing is that apportionment is supposed to be uniform across all states. What I have seen more often than not is that you DON'T need it unless you are over 26000 lbs.
I tried to find it on CO's website but could not. I would keep searching and find out what your home state says.
This is what NJ says:
Do I need an IRP (apportioned) vehicle registration?
"Apportioned Vehicle" means any vehicle, except recreational vehicles, vehicles displaying restricted plates, buses used in transportation of chartered parties, and Government-owned vehicles, used or intended for use in two or more member jurisdictions that allocate or proportionally register vehicles and is used for the transportation of persons for hire or designed, used or maintained primarily for the transportation of property and:
* Is a power unit having two axles and a gross vehicle weight or registered gross vehicle weight in excess of 26,000 pounds; or
NO.
* Is a power unit having three or more axles, regardless of weight; or
NO.
* Is used in combination, when the weight of such combination exceeds 26,000 pounds gross vehicle weight.
NO.
I spoke with a live person who said as long as I don't cross over the magical 26000 mark, no apportionment is necessary, even if I cross state lines. She also noted that while it's not necessary, it might save me some hassles on the road.
The people in NJ said I can't do IRPA (apportioned) without IFTA but other states don't suggest this. To me they should be completely different. I do not want to do IFTA so I am just not going to do either for now. I think if you do IRPA I think you have to keep track of the miles you travel in each state throughout the year.
More from NJ:
Vehicles, or combinations thereof, having a gross vehicle weight of 26,000 pounds or less and
two-axle vehicles and buses used in transportation of chartered parties may be proportionally
registered at the option of the registrant.
It's too bad the states can't get this all exactly the same
