The hottest election contests in Virginia are over whether the state should change the way it builds and manages its transportation system. Polls are open from 6 a.m. to 7 p.m. tomorrow.

The Tax

If a majority of voters in nine Northern Virginia jurisdictions approves, the sales tax will be increased a half-cent to 5 cents per dollar. Proponents say that would generate $5 billion over 20 years to finance road and transit projects within the region. Voters in the Hampton Roads area will vote on whether to increase the sales tax by 1 cent per dollar, to raise $7 billion for transportation projects.

If Approved

The tax money would go to new regional authorities, which would share responsibility for the state's transportation network with the Virginia Department of Transportation. The Northern Virginia Transportation Authority would be required to spend $2.8 billion on projects listed in the law that created the referendum. The authority's board, which includes the elected leaders of the nine jurisdictions, has set guidelines for further spending. A jurisdiction can veto a project within its boundaries.

If Defeated

Rejection of the tax leaves the current system intact. VDOT would continue to be responsible for building and maintaining the state's transportation network. The department's money comes from federal and state gasoline taxes, vehicle title fees, license tag fees and a half-cent of the current sales tax. Other revenue sources include bond sales based on anticipated federal revenue and a portion of the tax on insurance premiums.

On the Web

The Post's Voters Guides were published Thursday in the Extras and are available on The Post's Web site, www.washingtonpost.com. A primer on the Virginia tax referendum can be found at www.washingtonpost.com/vavoters.