As it works to convince you to institute a 10-cent gas tax on May 17, City Hall wants everyone to know it's not letting enormous trucks off for free.

Sure, those trucks wouldn't have to pay the tax, but now we've got our first look at how the city will look to make them pony up. The Portland Bureau of Transportation is circulating a proposal [PDF] for a "Portland Heavy Vehicle Use Tax" that would tack on an additional percentage to the state fees truckers already pay.

By taxing 2.8 percent of the weight-mile fee trucking outfits pay the state for their abuse of state roads, the city thinks it can pull in the $2.5 million a year it says is heavy trucks' fair share of road repair. Taken in tandem with the gas tax on the ballot next month, the plan could result in $18.5 million a year targeted to city streets in the next four years—a fraction of Portland's estimated need for road repairs, but also the most progress Portland's seen toward corralling more cash for transportation in a decade or more.

Even if the gas tax fails, PBOT says, the business tax plan will move forward. Truckers have said they oppose it.

The proposed heavy vehicle tax is one of several plans for taxing truckers the city has considered. We reported earlier this year on a proposed fee on tanker trucks as they picked up bulk shipments of diesel at Northwest Portland tanker farms.

Instead, Portland Transportation Commissioner Steve Novick has settled on a plan widely considered more fair (the load fee would have effectively taxed diesel customers around the state). The city plans to append the tax to the business license tax it already charges for the right to deliver products by truck within Portland city limits.

"The heavy vehicle use tax can be applied to businesses based in Portland and to businesses that ship to Portland addresses," reads a fact sheet about the proposal.

To calculate the tax, the city says it will charge businesses 2.8 percent of the weight-mile tax they pay to the State of Oregon for highway upkeep. So if that annual state tax is $10,000, the city says, an additional $280 would come to PBOT.

"Due to the fact that a relatively small number of businesses account for most of the heavy truck activity and therefore most of the costs associated with heavy trucks, most businesses will pay a relatively small amount," the fact sheet says. "On the flip side, a handful of very large trucking businesses will pay more based on their volume of trucking activity."

One potential issue with this proposal: There are a decent amount of scofflaws out there who don't pay for Portland business licenses even though they make truck deliveries in town. That's according to Jana Jarvis, president of Oregon Trucking Associations, Inc. In a recent email to members about the city's proposal, Jarvis noted: "Many of you may not be paying this tax today, as the evasion rate is high."

The city seems to think that its new tax will change that. "Many in the trucking industry believe that establishing this program will increase the number of businesses that should be paying this fee," the city's fact sheet says.

Portland City Council will take up the new tax May 4, according to PBOT spokesperson John Brady. It doesn't require a vote of the people to go into law, he says.