Megan Tribble votes at Charles Houston Recreation Center in Alexandria on Tuesday. (ASTRID RIECKEN/For The Washington Post)

Voters are choosing candidates in a slew of potentially high-impact primary elections in Virginia on Tuesday, including contests for Alexandria mayor, two members of the Arlington County Board and a number of positions in the state legislature that could determine control of the Senate.

Polls opened at 6 a.m. across Virginia and closed at 7 p.m.

Perhaps the highest-profile race in the state is one 50 miles south of Washington that pits Republican House Speaker William J. Howell against his onetime political protege, former Stafford County supervisor Susan Stimpson, whose campaign aims to harness the same tea-party-driven disaffection that last year helped Dave Brat oust then-U.S. House Majority Leader Eric Cantor.

A Howell loss would portend a difficult road for state and national Republicans trying to compete in the 2016 presidential contest in a crucial state that has not voted red in a statewide election for six years. But with more than half of precincts reporting Tuesday night, Howell held a wide lead.

More immediately, however, several state Senate contests with primary elections Tuesday could determine control of the state legislature’s upper chamber.

And in Arlington and Alexandria, primary elections for mayor and county board are seen as highly likely to produce the eventual winners in fall elections, given both communities’ solidly Democratic makeup.

Turnout was light in many precincts, especially compared to elections where a presidential, Congressional or gubernatorial contest is on the ballot. But those who did cast ballots took the process seriously.

“I’m voting because I can’t not vote,” said Susan Liss, a retiree who cast her ballot at Fairlington Community Center in Arlington and said her political involvement dates back to when she volunteered for John F. Kennedy as a high school student. “I have a 28-year-old son, and I don’t like the world I am leaving to him.”

Megan Tribble, who voted at the Charles Houston Recreation Center in Alexandria, called voting “my civic duty.”

“I don’t ever want to miss an election,” Tribble said. "This election has fewer voters, and my vote counts more."

Here are the key races:

Alexandria

A hard-fought Democratic primary for mayor has pitted three well-known politicians against one another. Four-term Mayor William D. Euille, facing a primary challenge for the first time in 12 years, is campaigning on his record of bringing big, long-planned projects to closure, such as choosing a location for a new Potomac Yard Metrorail station and the passage of the waterfront redevelopment plan.

Euille raised more than $200,000 to hold off former mayor Kerry Donley, who argues that the pace of economic development needs to pick up if Alexandria wishes to solve its fiscal imbalance,and Vice Mayor Allison Silberberg, who says historic areas and existing neighborhoods need to be protected.

With nearly 8-0 percent of the vote in, Euille and Silberberg were neck-and-neck, with Donley a distant third.

Arlington

Six Democratic candidates vying for the party nomination to the Arlington County Board define themselves as progressive fiscal watchdogs. It’s the first time in 30 years that two seats are open on the five-member board.

Katie Cristol, Christian Dorsey, Peter Fallon, James Lander, Andrew Schneider and Bruce Wiljanen want to succeed Chair Mary Hynes (D) and Vice Chairman J. Walter Tejada (D). Few policy differences have separated the candidates during the campaign, which has focused more on the issues each would tackle first. But even there, there are similarities.

Cristol, who at 30 is the youngest candidate, said the board needs new energy and to pay more attention to economic challenges of both young and old. Dorsey wants to focus on basic services and keep spending in check so money will be available for schools and affordable housing. Fallon, who has served on the housing, transportation and planning committees, said he’ll use his expertise to ask hard questions and rebuild trust with citizens. Lander has interests in attracting new businesses to Arlington and improving bus connections across the county. Schneider wants school improvements, better business growth, better “customer service” from county staffers and less intra-county factionalism. Wiljanen calls himself the mature, common-sense candidate who best represents ordinary residents.

Senate

Both parties are closely watching a three-way Democratic primary for a seat held by Sen. Charles J. Colgan (D), who is retiring after 40 years in the Senate. The district spans Prince William County and Manassas City. Michael Futrell, a former delegate, is running against Jeremy McPike, a volunteer firefighter and emergency medical technician, and Atif Qarni, a math teacher and former Marine.

Three Democrats are also vying for a seat held by retiring Sen. John C. Watkins (R), who represents one of the most evenly divided districts in the state, including parts of Richmond, Powhatan and Chesterfield.

Daniel Allen Gecker, a Chesterfield County supervisor, took a wide lead against rivals Emily Francis and Alex McMurtrie with about half of precincts reporting.

In a Senate district that includes parts of Richmond, Chesterfield and Petersburg, incumbent Democrat Rosalyn Dance faces a challenge from former delegate Joe Preston. Results from about a third of the district had Dance far ahead.

Joe Morrissey, the former lawmaker who fathered a child with a woman nearly 40 years his junior and won his last race from jail, is also running as an independent.

Republicans have their share of competitive primaries with four candidates vying to represent the Henrico area in a seat held by retiring Sen. Walter A. Stosch (R). And a longtime conservative target, Republican Sen. Emmett Hanger of rural Augusta County, is facing two challengers in the GOP primary there.

With two-thirds of precincts reporting, tea party-backed rival Amanda Chase is leading state Sen. Steve Martin, who also faces a challenge from businessman Barry Moore.

House of Delegates

In the Shenandoah Valley, conservative Del. Mark Berg faces a challenge from a more centrist GOP candidate, Christopher Edman Collins, a former Frederick County supervisor, who has raised more money than the incumbent. A win by Collins, along with Howell, could bolster establishment Republicans trying to fend off efforts by conservatives to control the state GOP.

A crowded field of five Democrats are in a race to replace Del. Rob Krupicka (D), who announced he won’t run for reelection because he has opened a doughnut shop, in a district divided between Alexandria, Fairfax County and Arlington. They are: Julie Jakopic, a consultant who ran two campaigns for Krupicka; Democratic Party leader Clarence Tong; Alexandria’s director of communications, Craig Fifer; former congressional candidate Mark Levine, and Larry Altenburg, an executive at an security technology firm. In Fairfax, two Democrats are vying to replace Del. Scott A. Surovell (D), who is running for Senate. They are Justin Brown and Paul E. Krizek.

Fairfax County

Supervisor Penelope A. Gross (D-Mason), a five-term veteran on the Fairfax County Board of Supervisors, will have to beat a tough competitor Tuesday if she wants to reclaim her seat. Jessica Swanson, a political newcomer who works for the D.C. public school system, is challenging Gross for the Democratic nomination, arguing that the incumbent has failed students in her district by consistently voting to underfund local schools during her tenure. Gross has countered that Swanson has received a large chunk of her funding from a Washington-based group and isn’t actually a local candidate. Swanson has also challenged Gross on her proposed redevelopment plan for Seven Corners.

In Fairfax’s Mount Vernon district, four Democrats are vying for the seat of Gerald L. Hyland, who is retiring after serving nearly 30 years on the board. Local business owner Candice Bennett, county Human Services Council member Jack Dobbyn, Fairfax County School Board member Daniel G Storck and Planning Commissioner Tim Sargeant are all bidding to represent the district that is divided by the Fort Belvoir military base.

The winner of the crowded primary in the largely Democratic district, which stretches south from Alexandria into Lorton, will face Republican nominee Jane Gandee in the general election.

Prince William County

Democrats Andrea O. Bailey, a local business owner, and Derrick R. Wood, a Dumfries town councilman and Marine veteran, are competing for the Democratic nomination representing the Potomac district on the Republican-dominated Prince William Board of County Supervisors — the board’s only primary this Tuesday. The winner will face longtime Republican incumbent Maureen S. Caddigan in the general election.

Astrid Riecken contributed to this report.