Along with the five-year federal transportation budget passed by Congress and signed into law by President Obama last week comes a good deal of hopeful thinking.

Rather than do the heavy lifting in front of voters to increase the federal portion of the gas tax, which has held steady at 18.4 cents per gallon since 1993, the funding package Congress assembled includes less reliable sources of funding, such as sending collection agencies after tax scofflaws and selling 66 million barrels of oil from the federal Strategic Petroleum Reserve under the assumption that the price of oil, now scraping the bottom of the barrel, will increase enough for such a sale to bring in $6.2 billion in the next 10 years.

Washington state legislators, apparently made of stronger stuff than their D.C. counterparts, earlier this year passed a gas tax increase that will fund the state’s own $16 billion, 16-year transportation spending plan. The state is now collecting 44.5 cents per gallon and will tack on another nickle next summer.

But it’s dawning on many that the gas tax has lost its ability to adequately fund the maintenance and further development that our state’s transportation infrastructure will need over the next 25 years.

The gas tax has three problems:

It’s set at a fixed rate that isn’t adjusted for inflation, eroding its purchasing power;

People are driving less often and fewer miles, and consequently buying less fuel and paying less tax;

Vehicles’ increased fuel efficiency and the growing popularity of electric and hybrid vehicles has likewise had an impact on gas tax revenue.

It’s why the Washington State Transportation Commission and the Puget Sound Regional Council are considering replacements for the gas tax, including an increased use of tolling, a carbon emissions tax, vehicle fees and charging drivers by the mile, perhaps using GPS technology or something similar to the Good to Go transponders the state is now using to charge tolls on I-405’s HOT lanes and the Highway 520 floating bridge and Tacoma Narrows bridge.

A two-day Transportation Commission hearing this week in Olympia will begin the discussion of different options at 9 a.m. today, and 8:30 a.m. Wednesday at the Transportation Building, 310 Maple Park Ave. SE, on the Capitol Campus in Olympia. Public comment periods are at 4:45 p.m. today and at 12:15 p.m. Wednesday.

The Puget Sound Regional Council’s plan seeks to increase funding $62.4 billion between now and 2040, with new highway tolls, a gradual replacement of the gas tax with a pay-per-mile system, fare increases for ferries and transit and a 1.5 percent increase in the motor vehicle excise tax.

PSRC’s evaluation of its plan shows little impact on the time most would spend commuting to and from work. And it also shows an increase in the amount most drivers would spend on their daily work commutes, compared to current costs and other funding scenarios. That increase, particularly for solo drivers, might provide additional motivation to consider transit, and that’s added justification for Sound Transit’s expansion of its Link light rail service into Everett.

Because of earlier decisions to fund transportation projects with bonds, we’re going to need to keep the gas tax for the next 10 to 15 years to pay off those bonds.

But going forward we need to consider new sources of revenue to fund maintenance and new construction so we can keep going foward.