As long as we're still driving fossil-fuel vehicles, the way we pay for our roads is pretty straightforward: We fill up at the pump, and for the most part, a big chunk of the gasoline tax we pay goes toward building and maintaining roads.

What isn't nearly as transparent is how we fund rail, pedestrian rights of way, and other transportation solutions. And of course what happens with our road funding once we start plugging in en masse.

Washington State lawmakers have already, by the way, been looking at that question for electric vehicles like the upcoming Nissan Leaf, with a proposed $100 tax per EV per year.

Seattle is facing a four-million-dollar budget shortfall for non-car-related infrastructure; the city previously had a controversial "head tax," for which companies had to pay $25 for each of its employees who drove alone to work, but last year a downtown business association succeeded in repealing it.

Now transportation advocates are proposing a new way of doing it. Instead of having businesses pay it, they want a similar system to be administered via a payroll tax; simply put, those employees who commute alone would get a little more deducted each paycheck.

A number of cities have a fixed-rate payroll tax that goes toward public transit, but the tax on solo commuters is a novel approach.

Iacocca on E-bike

Admittedly, Seattle and parts of the surrounding Puget Sound region is one of the most traffic-choked regions in the country—due both to challenging terrain and environmental regulations, both of which make it more difficult to either plan new roads or transportation alternatives than in most other U.S. cities. Seattle is in the process of constructing a costly light-rail line that might help ease congestion.

What do you think of a tax for car commuting solo? Is it fair, or even legal?

[Sightline Daily]