If you itemize your taxes, there are some taxes you can claim on Schedule A line 7 that you may not be aware of.
- Seattle monorail tax ("Monorail")
- Sound Transit tax ("RTA Tax")
These taxes are special because they are based on the value of the vehicle and therefore qualify as a "personal property tax" from the IRS's point of view.
While you're on Schedule A, don't forget to claim your deduction for state sales tax on line 5. You can look up the local sales tax rate for any Washington address by using this handy web form on the State of Washington Department of Revenue site. If you prefer doing it the slow way, you can download all the local sales tax rates. If you live in King County†, for example, the local rate is 1.9%, or 2.3% if you live in an RTA area. (That's in addition to the state-wide 6.5% rate.)
†That's King County, Washington, USA of course. I would have thought that was clear from context (it's the county that Seattle is a member of, and I've been talking about the state of Washington the whole time), but I can never tell with you folks.