For commuters, September doesn’t arrive all at once. In fact, the summer lull on the D.C. area’s roads and rails begins to end in late August as many students return to school. And this year’s federal base realignments also began to show their effects in August.

But as this month evolves, the collective impacts of having everyone back at work will generate the tension we refer to as September Shock. It may occur when you find yourself stuck behind a left-turning school bus, or waiting an extra light cycle to get through an intersection or jamming aboard a Metrobus that was late and loaded with passengers.

For many, the shock lasts only as long as it takes to shake off summer travel habits and reset behavior. But this September, there are a few particular concerns.

Bethesda’s National Naval Medical Center. Patients and staff have been shifting over to Bethesda from Walter Reed Army Medical Center as part of the base realignment. While some work has been done to ease the traffic impact, the main efforts are still to come. For now, travelers will see new sidewalks and new traffic signals. The reopening of the Cedar Lane bridge, which was closed for repairs over the summer, should be a help for many drivers.

Capital Beltway bridge. Work began in late spring on the Northwest Branch bridge between University Boulevard and New Hampshire Avenue in Silver Spring. All eight lanes are open at rush hours, but drivers encounter lane shifts and shortened merges. Maryland often stations a camera enforcement van along the side, to enforce the 55 mph speed limit through the work zone.

Alexandria’s Mark Center. This is another of the base relocation sites close to D.C. Here again, there are plans to improve the traffic flow, but most of those plans haven’t evolved into construction projects. Several bus routes have been modified to make transit use easier, but the Mark Center still is not a transit hub. The center overlooks Interstate 395, one of the region’s main commuter routes. I-395 really didn’t need any extra help to be a trouble spot for drivers.

Fort Belvoir. As with other base realignment programs, the one sending thousands more people to Fort Belvoir offered relatively little time to make transportation improvements in an area that lacks extensive transit service. But in this case, an extension of the Fairfax County Parkway has opened and a portion of Interstate 95 to the south has been widened. Long-term, Virginia is planning to convert the I-95 HOV lanes to high-occupancy toll lanes, but any positive effect of that is well beyond 2011, let alone September.

Dulles Toll Road/Capital Beltway. The reconfiguration of the interchange was a top complaint among commuters in late spring. The Virginia Department of Transportation then made some modifications in this HOT lanes work zone to ease the congestion, but many drivers think the fundamental problem has not gone away, and they fear September traffic. Their main concern is about the space taking up by the work zone on the left side heading east on the Toll Road.

I’d like to hear your reports from these areas, and help me identify other trouble spots.