The planning board that oversees regional transportation projects on Wednesday advanced a modified High-Occupancy Toll (HOT) lanes plan along I-95, as well as a reversible on-off ramp to increase access to the Mark Center in Alexandria.

Under the first project, a $1 billion public-private plan, HOV/HOT lanes would eventually extend from about two miles north of I-495 to Route 610 in Stafford County. Construction is projected to start in 2012 and could be completed as early as 2015. A federal environmental review is also required.