Everybody knows Republicans never, ever want to raise taxes. In our region, however, there’s an important exception to that rule.

Much of the GOP leadership in Northern Virginia is perfectly willing to increase taxes — providing the money is guaranteed to go for roads and mass transit to combat our area’s crippling traffic backups.

But there are two obstacles. One is that Republicans elsewhere in the state won’t let it happen. The other is that a tax increase might have to win Fairfax voters’ approval in a referendum, which has proved difficult in the past.

This political dynamic was well illustrated in a spirited discussion Tuesday during a two-day retreat of the Fairfax County Board of Supervisors. One of the board’s most fiscally conservative members, John Cook (R-Braddock), openly endorsed the idea of seeking $230 million a year in new taxes over the coming decade to widen roads, build interchanges and add mass transit.

“This is a framework we could use to have a county-wide discussion,” Cook said enthusiastically. “The numbers are falling together. We might not like them, but they’re beginning to add up.”

Cook urged a deal in which the state legislature would empower the Fairfax supervisors to impose taxes on restaurant meals, and other levies and fees. In return, the county would take over responsibility for maintaining its own roads.

It was great to hear a Republican politician acknowledge the need to raise revenue to provide public services.

“The number one thing that people want us to do is fix the roads. It’s going to take some money,” Cook said.

But such a trade-off would almost certainly run afoul of GOP anti-tax purists, mostly from outside Northern Virginia, who dominate the General Assembly. Just as they would not raise taxes themselves, most Republicans in Richmond would not allow Fairfax (or anybody else) to do so.

“I just don’t think that this Assembly, with both houses controlled by Republicans, is going to approve it. I think that counting on it, or even thinking it’s going to happen, is just crazy,” Supervisor Michael Frey (R-Sully) said.

It’s not just the downstate GOP. The Fairfax supervisors already have the legal authority to ask voters to approve a meals tax in a referendum. But Fairfax voters rejected tax increases in ballot measures in 1992 and 2002, and politicians of both parties are wary of risking another loss.

In light of that, and after hearing the supervisors’ discussion at the Lorton Workhouse Arts Center, it was hard to be optimistic about the chances of reducing the gridlock in Northern Virginia.

An opening presentation by Fairfax Transportation Department Director Tom Biesiadny said the county was $3 billion short over the next 10 years of what was needed to improve roads and transit as the county desires.

There isn’t enough money for a long list of projects such as widening Route 7 near Tysons Corner Center and extending Frontier Drive near Springfield Mall. Many roads that should be repaved are merely being patched. That makes it more likely they’ll have to be completely rebuilt in the future, at much higher cost.

“Every day we wait, our roads are deteriorating. We’re going to be rebuilding roads, not resurfacing them,” Jeff McKay (D-Lee), chairman of the board’s transportation committee, said.

If there’s any hope, it’s in the bipartisan willingness in Fairfax to pay higher taxes of some sort if it means actual, visible improvements in the roads.

Mike Lewis, a Republican and vice chairman of the Fairfax County Economic Development Authority, said the area business community has long wanted tax increases to be considered as a way to address congestion.

“What John [Cook] is suggesting is not inconsistent with many more conservative views in Northern Virginia, as it relates to transportation,” Lewis said.

I heard similar opinions from voters in Cook’s district whom I interviewed Friday at Burke Centre Shopping Center. Even self-described conservatives said they’d pay more in taxes if they were confident it would all go for roads.

“I need a guarantee I’m going to get a return on my investment. They can’t raise my taxes and then give the money to someone or something else,” said Christopher Yurasko, 32, a life-insurance salesman.

Larry Grimes, 63, a retired government worker and registered independent, was frustrated by what he saw as excessive anti-tax sentiment in the state.

“A problem with Virginia is that too many people think you can continue to cut taxes and expect to have increased services. The money thing doesn’t work that way,” Grimes said.

When it comes to roads, even conservative leaders in our area have recognized that reality. The traffic can’t get fixed in Northern Virginia until downstate Republicans and local voters accept it, too.