The voter-approved increase, a nickel per $10 purchase, bumps the total rate past 10 percent in Seattle, Tacoma and several north-end communities.

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The voter-approved Sound Transit 3 sales tax increase takes effect Saturday, bumping the total rate past 10 percent in Seattle, Tacoma and several north-end communities.

In all or parts of some 30 King County cities, from Bellevue to unincorporated places such as White Center and Skyway, the rate will hit exactly 10 percent.

Sound Transit 3 raises the sales tax 0.5 percent, or a nickel per $10 purchase — while also increasing property taxes and car-tab taxes in the urban Puget Sound area, adding to several existing taxes for local transit providers.

The $54 billion plan promises to deliver seven light-rail extensions over a quarter-century: Everett, Redmond, south Kirkland, Issaquah, Tacoma, West Seattle and Ballard. Commuter-train stations and capacity would be added on the south Sounder line, along with park-and-ride stations and an Interstate 405 bus-rapid transit corridor.

Traffic Lab is a Seattle Times project that digs into the region’s thorny transportation issues, spotlights promising approaches to easing gridlock, and helps readers find the best ways to get around. It is funded with the help of community sponsors Alaska Airlines, CenturyLink, Kemper Development Co., NHL Seattle, PEMCO Mutual Insurance Company, Sabey Corp., Seattle Children’s hospital and Ste. Michelle Wine Estates. Seattle Times editors and reporters operate independently of our funders and maintain editorial control over Traffic Lab content.

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About two-thirds of your total sales tax goes to Washington state for education, social services, prisons, environmental agencies and other functions. About one-fourth funds transit and the rest is for city or local services.

The new combined rate for Seattle and Tacoma shoppers is 10.1 percent.

The top rate is 10.4 percent in Lynnwood, a big retail destination that includes Alderwood mall. Voters there also passed a 0.1 percent sales tax for local streets last year.

Mill Creek residents also will pay 10.4 percent.

Both cities, along with neighboring Edmonds, Mountlake Terrace, Brier and Mukilteo, belong to the Community Transit district, where voters passed a 0.3 percent boost in 2015.

Rising sales taxes are one reason Washington’s tax system consistently ranks as the most unfair, or “regressive,” meaning that poorer people spend a larger share of their income on taxes, compared to the rich.

Transit campaigners say that packages like ST3 benefit the masses who can save money by substituting buses and trains for a car. But the costliest fixed-rail lines miss many working-class suburbs, and people who commute cross-county rather than downtown.

Besides sales taxes, ST3 raised the car-tab tax to $110 per $10,000 of vehicle value — but the tax rates are based on a depreciation schedule that overvalues newer cars, compared to the market or Kelley Blue Book value. State lawmakers have filed proposals this session that would reduce the tax bills.

And property taxes will rise this year by $25 per $100,000 of assessed home value, but increases are limited to 1 percent a year after 2017.

Overall, this year’s ST3 increases total an average $326 per median household, or $169 per adult.

You can estimate your own ST3 increase by using The Seattle Times calculator posted at seattletimes.com.