Gov. Bob McDonnell's endorsement of Del. Tim Hugo's bold plan to replace Virginia's 17.5-cent gas tax with a slight increase in the state sales tax -- from 5 percent to 5.8 percent -- is under attack from all sides. But the commonwealth has little choice. It has painted itself into a corner by underfunding transportation even as it was doubling the state budget.

Since 2002, the General Assembly transferred $3 billion from the commonwealth's highway construction fund to fix potholes and repave existing roads. In a few short years, maintenance will consume every available transportation dollar. Thanks to the increasing fuel efficiency of vehicles, gas tax revenue has been steadily declining, so something obviously must be done.

Democrats correctly argue that the sales tax is regressive. Of course, that didn't stop them from enthusiastically supporting then-Gov. Mark Warner's unsuccessful regional sales tax referenda, specifically targeted for transportation improvements in Northern Virginia and Hampton Roads in 2002. Senate Democratic Leader Dick Saslaw should explain why raising the sales tax for transportation was such a good idea under a Democratic governor, but not under a Republican governor.

Another argument is that the poor are more likely to be carless. But this ignores the fact that the carless depend on well-maintained roads as much as anyone else, if they ever use or have need for school or commuter buses, police cars, firetrucks or ambulances. Even people who don't drive benefit from road funding, since virtually all necessities of life are delivered by truck.

Saslaw has also disingenuously insisted that transportation funding be kept completely separate from the state's General Fund. But lawmakers in Richmond have repeatedly raided the Transportation Trust Fund whenever it suited them and refused to pass legislation to make it truly off-limits. So the separation that Saslaw insists upon is a fiction.

Republicans rightly object to raising taxes on recession-battered taxpayers. Hugo's bill is based on a revenue-neutral trade-off. McDonnell's version, which raises $3.1 billion over the next five years, includes an unwarranted tax on Internet sales that should be stripped out before passage.

Transportation has been consistently short-changed in Virginia for decades, even though it represents one of the state's core functions. This cannot continue. And as sales tax receipts rise due to expanded economic activity, revenue for new roads and bridges will be generated to keep the vast highway network Virginians depend upon healthy for years to come.