OLYMPIA — When Mark Harmsworth went online earlier this month to renew the tabs for his 2014 Ford F350 pickup, he did so with trepidation.

The Republican state representative from Mill Creek knew plenty of people hit with skyrocketing bills due to last fall’s voter-approved car tab increase to pay for Sound Transit’s next round of expansion.

And he’s pilloried the regional transit authority for making matters a little worse by calculating its motor vehicle excise tax using an outdated formula that inflates the value of cars.

But even he didn’t expect what he saw when he looked at the amount due. It was $2 less than he paid in 2016.

“It was $108. I thought that doesn’t sound right,” he said Wednesday. “I was expecting to see $600 or $700 for my tabs.”

No mistake had been made.

He owed less because his truck is one of the many types of vehicles exempted under state law from paying the Sound Transit motor vehicle excise tax.

He knows he isn’t completely off the hook. Tabs on his family’s passenger vehicles will be due later this year. And he fully anticipates those fees will rise as a result of increases in Sound Transit 3 which aims to eventually bring light-rail service to Everett.

But the truck is exempt from the 1.1 percent excise tax rate under a provision covering trucks with a scale weight between 6,000 and 12,000 pounds. Other provisions exempt campers and off-road vehicles; cars registered to tribal members, disabled veterans and nonresident members of the military; and rental cars.

As of December, there were 174,615 registered powered vehicles in Sound Transit’s boundaries not subject to the tax, according to the state Department of Licensing.

The total included 61,076 passenger vehicles, 37,572 commercial vehicles, 34,823 trucks and 15,212 off-road vehicles. There also were 3,522 mopeds, 2,028 all-terrain vehicles and 5,493 snowmobiles.

To be clear, state lawmakers and not Sound Transit leaders made it possible for Harmsworth and others to catch this break.

Washington collected a statewide motor vehicle excise tax, or MVET, long before the birth of the regional transit authority. Lawmakers identified various types of registered vehicles that would not be charged. When Sound Transit started collecting its own excise tax in 1997, it was required to honor the exemptions in law at that time.

Passage of Initiative 695 — the $30 car tab ballot measure championed by Tim Eyman of Mukilteo — set in motion the eventual elimination of the state-imposed MVET.

But the exemptions remained on the books. Sound Transit has not attempted to change the law and has no plans to try in the future, an agency spokesman said.

Sen. Steve O’Ban, R-University Place, has led efforts in the Senate to reform how Sound Transit is governed and to force it to use a different vehicle valuation method. He learned of the exemptions from Harmsworth.

“That sounds bizarre to me,” he said, after hearing how many thousands of vehicles aren’t taxed.

Neither lawmaker intends to rewrite the law to reduce or eliminate exemptions. But Harmsworth said his experience highlights a need for cleaning up and clarifying statutes involving Sound Transit operations.

“It’s not well put together,” he said. “I just think this shows the incompetence of the way it was set up.”

Jerry Cornfield: 360-352-8623; jcornfield@heraldnet.com Twitter: @dospueblos.

This story has been corrected to reflect the fact motor homes are not exempt from the motor vehicle excise tax imposed by Sound Transit.