Part of the reason for the big disparity between heavy trucks and cars in Idaho on paying their fair share for roads: The repeal of the weight-distance tax in 2001, as a result of a lawsuit. Since then, heavy trucks have paid only registration fees. Idaho's last formally published highway cost-allocation study in 2002 didn't fully reflect that change, consultant Patrick Balducci told the governor's transportation funding task force today. An unpublished state highway cost allocation study in 2007 showed figures between the 2002 study and the new one, he said, which provides additional evidence of the trend toward cars paying more and trucks less.

Another factor: More construction, partly as a result of the GARVEE bonding program. When pavement or bridges are replaced in major construction projects, more of the cost of that is allocated to trucks than to cars, Balducci explained, "because of the ratio between axle weights and pavement damage." That's as opposed to costs for signals or general highway operations, which are attributed more equally to all types of vehicles. Also, the bonding program was focused on the interstate system, Balducci noted, which sees more heavy-truck travel. He also noted on big trucks the "data that they're going to do much more damage than the lighter vehicles."