I've already written about the boon to state tax revenues should the Marketplace Fairness Act (MFA) pass the US House, enabling Washington State to collect an additional $567 million in taxes on the purchase of out-of-state goods in the 2015-17 biennium. But the so-called "Internet Sales Tax" would also prove a boon to local governments that have been slowly starved by a sales tax base that has been steadily shrinking as a portion of the overall economy.

According to the latest Washington State Department of Revenue projections, local governments would collect an additional $27.3 million in 2014, rising to $158.5 million in 2017 once businesses reach 90 percent compliance.

So what does this mean here in Seattle and King County? Well, King County accounts for about 40 percent of total taxable sales statewide, and Seattle accounts for about 39 percent of King County sales. So extrapolating from DOR's numbers, the following local revenues can be roughly approximated:

Additional Local Internet Sales Tax Revenue (in Millions)
Seattle (.85)$1.2$3.2$5.2$6.9
King County (.15)$0.5$1.5$2.4$3.2
Metro (.9)$3.3$8.7$14.4$19.0
Sound Transit (.9)$3.3$8.7$14.4$19.0
Criminal Justice (.1)$0.4$1.0$1.6$2.0
Mental Health (.1)$0.4$1.0$1.6$2.0
Total (3.0)$10.9$29.1$48.0$63.4
(Only Seattle city taxes shown, thus columns won't add up.)

It's a rough extrapolation based on projected revenues. And not all of King County levies the full 3 cent per dollar local sales tax, so that muddies my calculations a touch. But it's certainly in the ballpark. And the biggest takeaway is that the MFA would raise a substantial amount of money to build and operate local transit—an additional $38 million a year for Metro and Sound Transit combined by 2017. You know, give or take.

That's not enough to solve all our problems; Metro alone faces a $75 million shortfall in 2014. But it makes a big dent. And to be clear: This is not a new tax! The MFA merely enables state and local governments to collect a tax consumers already owe, but overwhelmingly don't pay. And now that they've worked out the kinks so that it's no longer a burden on small retailers, it's hard to see the moral or economic argument against it.