I tend to believe the assessment of Robert Pitcher, VP of the American Trucking Association, that Rhode Island legislators intended for a fee reduction on truck registrations to be an insider gimme to in-state truckers, not “to apply to vehicles based outside the state.” As the Trucking Association describes the problem:
“The new section 31-6-1.1 lowers the fees for trucks and tractors registered in RI,” said Pitcher. “This includes trucks and tractors registered under [the International Registration Plan (IRP)] and based in  states other than RI, all of which are under the Plan registered in RI to which they pay fees for all travel in RI. And of course, this means a reduction in registration fees for a whole lot of trucks — including tractor trailers running through Rhode Island on the interstate.”
Everybody’s been focusing on the incompetence of this poor drafting of the law (if it proves to have the warned-of consequence). The effort to bring in new revenue from tolls may have the effect of removing existing revenue from registrations.
On reflection, though, maybe that’s not such a bad thing. Any money not collected for more-general purposes and dedicated to maintaining infrastructure is a good thing, and if the trade is entirely within the tax-and-fees structure for commercial trucks, so much the better.
Of course, the trick would be to prevent the state from making up for the lost revenue from registrations by increasing registration fees on others or just increasing taxes on everybody. That would just make the whole tolling fiasco ultimately an increase of general taxes.
I wish I could be confident that Rhode Islanders could prevent the state government from ratcheting up revenue in this way, but given that we don’t have a legitimate representative democracy, we’ll just have to continue watching the blundering as insiders move to fix the holes the poked in their graft boat.