Better gas milage = less gas tax, because less gas is purchased, so there is less tax... Surprise!
The trend toward lower gasoline consumption is like a flashing yellow light in the new 20-year plan from the Washington Transportation Commission.
To improve or even maintain mobility in the state, the commission is recommending new ways to raise money beyond the gas tax: wider use of toll charges, a new vehicle excise tax, local tax options and a tax on alternative- fuel vehicles.
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As gasoline use drops, so does state revenue, Seattle Times Newspaper