Esteban Garces and L. Mark Dudenhefer agree on this much, and perhaps only this much, as they vie for one of Northern Virginia’s three new House of Dele­gates seats: Traffic stinks.

For Garces, a 30-year-old community organizer for Tenants and Workers United, the answer is more Metro transit, with the state picking up some of the tab. Dudenhefer, a 59-year-old ex-Marine, favors free-market solutions, like the system of organized hitchhiking known as “slugging” that gets him to and from his defense-contracting job in the District.

Their race for the 2nd House District will be among Virginia’s most watched, drawing the attention of far-off politicos who experience Northern Virginia commuting woes only from the blissful distance of a “Worst Traffic Cities” ranking.

All eyes will be on the 2nd and two other Northern Virginia districts — the 10th and 87th — places that helped send Democrats Barack Obama to the White House and Mark Warner to the Senate in 2008, then turned around a year later and played a role in making Republicans Robert F. McDonnell and Ken Cuccinelli II governor and attorney general, respectively.

Freshly relocated — through redistricting — from dwindling downstate regions to the fast-growing Washington exurbs, these three swing districts cover territory crucial in next year’s races for president and U.S. Senate. As these seats go, some political observers say, so goes the state.

“I think you have to look at these elections as saying something important about how these exurban districts are trending,” said Bob Holsworth, a retired Virginia Commonwealth University political scientist.

Even as experts prepare to parse this trio of House races for clues to how purple Virginia may go in 2012, some caution against reading too much into the tea leaves. They contend that a number of factors make local elections imperfect predictors of statewide and national politics. Low voter turnout, a focus on bread-and-butter issues such as transportation, and the lag time between “off-year” elections next month and presidential-cycle races can make local contests less-than­reliable barometers, experts say.

“The concept of a bellwether district is very disturbing to me because it’s a coincidental statistical relationship,” said Craig Leonard Brians, associate professor of political science at Virginia Tech . “Some county in Ohio for 25 presidential elections, however it went, the rest of the country went. But that’s just a coincidence. There used to be five or six counties like that, but pretty soon they changed. Are they actually representative of the rest of the rest of the country? No, they’re not. ”

Even if the House races accurately take each district’s temperature on national and statewide races, a lot can happen in a year, said Stephen J. Farnsworth, an associate professor of communication at George Mason University.

“What we can see from this election is whether or not the Republican enthusiasm we saw in 2009 and 2010 is still in place,” he said. “And certainly if it is in place, that’s a good sign for Republicans in 2012. . . . Enthusiasm matters a lot in politics — and it can disappear very quickly.”

While their predictive value is in question, there is no doubt that these districts swing — and give the prevailing party the chance to spin its wins.

Obama won the 2nd District by 57 percent. A year later, McDonnell took it by 58 percent. In the 10th and 87th, Obama won by 51 percent and 54 percent, respectively, while McDonnell won by 62 percent and 59 percent.

With the areas up for grabs, all three races have been hard fought.

In the 2nd District, which covers parts of Prince William and Stafford counties, Dudenhefer and Garces have laid out competing visions to solve the area’s transportation ills.

In the 10th District, which takes in parts of Loudoun, Frederick and Clarke counties, Republican Randy Minchew, a Leesburg lawyer, is promising to cut taxes and spending in Richmond. His Democratic opponent, Leesburg Town Council member David Butler, stresses the need to improve roads and add jobs.

In the 87th District, which covers parts of Loudoun and Prince William counties, Republican businessman David Ramadan says he wants to promote a pro-business climate. He faces Democrat Mike Kondratick, director of grass-roots advocacy for the Juvenile Diabetes Research Foundation in the District. Kondratick is focused on schools and transportation issues.

The candidates agree that transportation and jobs are top-rated concerns of voters. They have said that social issues have hardly come up as they’ve knocked on thousands of doors and attended community meetings. Minchew has distributed literature stressing his opposition to abortion, including a desire to outlaw the procedure if used for sex selection.

Although swing areas are not known as hotbeds for social issues, those matters could tip a close race, said Mark Rozell, a George Mason University political scientist.

“It’s an appeal to core voters to try to mobilize them,” he said. “Elections, of course, are fought at the margins, within 5 percentage points. Even if the social issues are not paramount . . . it could be the critical difference.”

Voter turnout tends to be sharply lower in off-year elections than during presidential or statewide races. Turnout in Virginia was about 75 percent when Obama was elected in 2008 and 71 percent when George W. Bush won reelection four years earlier. It ranged from 30 percent to 53 percent in the years in between.

“Because Virginia has an off-year election cycle, you’re looking at a situation where the election is a very, very distorted picture of the electorate,” Farnsworth said. “You’re talking about a swing of millions of people participating or not participating.”

Even so, there is a reason to pay attention to the three districts: They’re competitive. Unlike the deep rural areas that are GOP territory and the cities and close-in suburbs that tend to go for Democrats, Virginia’s exurbs are “contestable,” Farnsworth said.

“These particular races are really important races because they’re in the areas of rapid growth and in the areas where both parties are really pretty competitive,” he said.

The reason for that is the growing diversification of those areas, experts say.

“There used to be this very easy formula, as a place became more suburbanized, it became more Republican,” Holsworth said.

But that traditional dynamic has not held true in these districts because of the way they have developed: first with large estates, then with townhouses and apartments, Farnsworth said.

“The first people into Loudoun are much more focused on a conservative social agenda than the second wave, who may be just looking for a deal on a townhouse they can afford with their high-tech job,” he said.

When estate owners and apartment dwellers head for the same ballot box, observers say, there’s a level of unpredictability that makes for good politics-watching if not a crystal ball.

“The local races are strongly affected, of course, by broader trends, but ultimately they come down to local issues and personalities,” Rozell said. “If we see a big Republican sweep, sure that would be a strong indicator of a trending that could hold for next year. . . . [But ] the old-line attachments to historic traditions and personalties in state politics just aren’t there for many of the new voters.”