In the congested D.C. region, the planners of a road project face two basic challenges: There’s the problem they have to fix, and there’s where they have to fix it.

The problem along Arlington Boulevard near Fort Myer is easy for commuters to spot. There’s no room to do anything. In heavy traffic — and there’s often heavy traffic on this six-lane stretch with closely spaced intersections that aren’t really worthy of the name — drivers must give all their attention to accelerating along on-ramps, decelerating on exit ramps or just trying to inch forward along the through lanes.

Meanwhile, the work environment for road crews amounts to a crawl space. They’re out there behind orange barrels and cones, trying to keep the traffic flowing as they do their jobs while trying not to raise so much of a racket that they bother the thousands living in apartments and townhouses nearby.

This is what they’re doing and why.

The legacy

Arlington Boulevard (Route 50) was built in the 1930s as a four-lane divided highway. Then interchanges were added at 10th Street and Courthouse Road on the south side of Rosslyn, and the road was widened to six lanes.

The interchanges are close together, and the merge lanes are short. Drivers entering on the westbound side can’t get up much speed, but at least they’re approaching the travel lanes from the right-hand side. The drivers entering on the eastbound side merge with the left travel lane. So they’re attempting to reach highway speed while looking for traffic over their right shoulders.

Untangling this mess has been a transportation priority in Arlington County for more than a decade, and the county has been working with the Virginia Department of Transportation on a plan that now has become a $39 million project.

The fix

“This will be better,” Mel Harvey assured me as we looked over thick books of plans for Arlington Boulevard and the interchanges. Harvey is the VDOT construction engineer responsible for the project, which began last year.

When it’s all done in fall 2013, the rebuilt interchanges and boulevard will be safer and easier to drive and have more traffic-moving capacity, Harvey said. Unfortunately, they’ll still have those left-hand entrances on the eastbound side, but along with the other ramps, they should be lengthened to the point that drivers will have a much easier time getting on and off the boulevard.

The bridges over westbound Arlington Boulevard at 10th Street and Courthouse Road will be replaced. Acceleration and deceleration lanes will be added and separated from the main road.

Intersections controlled by traffic signals will provide access from eastbound Arlington Boulevard to 10th Street and Courthouse Road. Ramps will provide access from westbound Route 50. A “T” intersection, with signals, will control access from both directions of Fairfax Drive to the Courthouse Road ramp.

A bike path will be added to eastbound Arlington Boulevard between Pershing Drive and Rolfe Street. The westbound trail will be moved and extended under the 10th Street bridge.

Some enhancements have nothing to do with moving people but should make the traveling experience more pleasant. Watch for the artistry that will emerge in the metal grillwork and accent lighting for the bridges and in the sculpted panels of the concrete retaining walls. These are part of the Arlington Public Art program.

The work

“Each project has its own personality,” Harvey said. And he said he thinks this one has a fairly difficult personality, for its size. The tight workspace is a particular challenge, but the soil in some areas has been of poor quality for construction work, and utility relocations posed unexpected difficulties. While workers on other projects were benefiting from the mild winter, he and the other officials on the Arlington Boulevard job were dealing with the soil and the underground lines.

Meanwhile, they have been working on balancing the needs of the neighbors and the commuters, two groups that tend to have very different priorities.

The neighbors successfully petitioned for a change in a traffic detour. (The nearby streets are densely populated, and plenty of people are out walking. Many streets have 25 mph speed limits.) To limit nighttime noise and disruption, the project managers have tried to build in more room for daytime work while keeping the travel lanes open at peak periods.

Drivers may find up to two lanes closed in each direction on Arlington Boulevard from 9 p.m. to 5 a.m. weeknights.

The bridge from southbound 10th Street to eastbound Arlington Boulevard will be closed through late 2012 or early 2013. VDOT said drivers can detour by taking Washington Boulevard to North Pershing Drive and then get to the boulevard.

The ramp from westbound Arlington Boulevard to North Fairfax Drive between Courthouse Road and 10th Street also will be closed. Drivers can detour via 10th Street.

Fairfax Drive between Scott Street and Courthouse Road will be closed. Drivers can take North Scott Street to 13th Street North.

Drivers will not be able to make left turns from Courthouse Road to Fairfax Drive.

Traffic is scheduled to return to the rebuilt bridges in fall 2013.