The work zone for the express lanes is in the middle of I-95 in Northern Virginia. (Robert Thomson/The Washington Post)

We call it September Shock because of the cruel awakening to more congested roads, buses and train cars, but the effects of summer’s end don’t become apparent all at once.

The return comes in waves. On Tuesday, Virginia public school students returned to classes, but many students in Maryland and the District are into their second week. Congress isn’t due back till next Monday.

And the sheer number of commuters is only part of the story. The timing of commuting turned out to be a bigger factor, according to a study done by the regional Transportation Planning Board. During the long days of warm weather, with school out of session, workers are more likely to vary their schedules. When the weather cools, and the days grow shorter, people compress their commuting times into narrower windows, resulting in more congestion.

Metrorail and Metrobus ridership tends to drop in August, then rebound in September. We’ll be watching to see if the rebound has a noticeable effect on Metrorail, which opened the Silver Line in mid-summer.

Here are some tips for making your commutes a bit less shocking.

  • The takeaway from that planning board study on summer-fall commuting is that if you can vary your departure times this fall, you may have a better commute.
  • The Capital Weather Gang says commuters will get through this post-Labor Day week without the slightest hint of fall. Tuesday is likely to be the most uncomfortable day, but the high temperatures will hover around 90 degrees through Saturday.
  • Drivers may encounter a bit more congestion around the entrance to the new garage on the north side of the Silver Line’s Wiehle-Reston East station. But I’m more concerned about the potential for additional crowding on downtown platforms during the afternoon commute, especially when there’s a disruption in service affecting the Silver, Orange and Blue lines. Blue Line riders will only get more unhappy with the crowding, now that their trains operate every 12 minutes.
  • The seasonal change makes no difference in the ranking of road work delays. The champ still will be the 29-mile-long work zone for the 95 Express Lanes on I-95/395 in Northern Virginia. The project is scheduled to be done at the end of the year, with the express lanes opening in early 2015.
  • Some traditional trouble spots get less worse during the summer but will return to their full agony this month. Those include the Capital Beltway between I-95 and Georgia Avenue during the morning commute and the Beltway between Tysons Corner and Bethesda during the afternoon commute. Congestion will start earlier and be more intense than it was during the summer.
  • AAA Mid-Atlantic added these spots to the watch list for commuters: New York Avenue, Constitution Avenue, Independence Avenue, D.C. 295, the Southeast-Southwest Freeway, Rhode Island Avenue and Wisconsin Avenue in the District; northbound I-395 from Route 27 to Route 110 and the Beltway inner loop from Route 193 to the George Washington Parkway in Virginia. That stretch of the inner loop between Tysons Corner and the parkway also includes a work zone where the Virginia Department of Transportation is planning to open the shoulder lane to rush hour traffic. That project is scheduled to be done by the end of the year.
  • This fall, the District Department of Transportation plans to begin rebuilding the 16th Street Bridge over Military Road NW. The work will be done on an accelerated schedule, since it involves the junction of two important commuter routes, but it still will disrupt traffic for at least a few months.