Four new high-occupancy toll lanes -- once derisively called "Lexus lanes" -- will open Saturday on the Capital Beltway between the Springfield Interchange and the Dulles Toll Road. This is good news for every driver in Northern Virginia, including those who can't afford a Lexus and don't want to pay any tolls, because the increased capacity will speed up traffic for everybody.

Thanks to a public-private partnership between the Virginia Department of Transportation, Fluor Enterprises and Australian toll road developer Transurban, the 495 Express Lanes were completed on-budget and six weeks ahead of schedule. The private joint venture kicked in 80 percent of the $2 billion cost, leveraging public funds to replace 50 aging bridges and upgrade 12 key interchanges that would not have been financially possible otherwise. In exchange, Fluor-Transurban will pocket tolls for the next 75 years while VDOT retains ownership of the "highway within a highway."

About 225,000 vehicles currently crowd onto the Virginia section of the Beltway daily. That number is expected to increase to 400,000 by 2020. VDOT projections show that without the four new Express Lanes, that segment will be in gridlock 12 hours a day two decades from now, compared with five hours with the new Express Lanes.

The first dynamically priced toll lanes in the region will not just allow rich people to buy their way out of gridlock. For one thing, the lanes are free for buses, carpools and vanpools with three or more passengers, motorcycles and emergency vehicles. Those who need or want to get to their destinations faster will have the option of paying tolls, averaging $3 to $6 during rush hour, but those tolls will pay for the additional highway capacity that benefits everybody. Existing Beltway lanes will still be free but with fewer vehicles than they would have otherwise.

The Fairfax Board of Supervisors' Private Sector Energy Task Force recently admitted that only 5 percent of the county's 1 million residents live within a half mile of a transit station. That will be just 7.5 percent by 2040 -- even with the addition of the Silver Line. But thanks to decades of political and environmental opposition, highway capacity has not kept pace with the growing population.

That's why the Washington region now has the nation's third-worst traffic congestion. It will take more than 14 miles of Express Lanes to reverse that mistake, but they still represent a tangible -- and welcome -- improvement.