The commuting phenomenon we call September Shock may not come as a sudden jolt on the first trip after Labor Day, but during the next few weeks, travelers may find their nerves a bit more on edge.

As vacations end, school resumes and Congress returns, highways in the D.C. area will be more crowded; it will take longer to get through busy intersections; and transit riders will find trains and buses more congested.

View Photo Gallery: Children across the Washington area headed back to school for another academic year.

Meanwhile, road construction projects and Metrorail’s rehab program are as active as they were during vacation season.

Another contributor to the September slowdown is the newness of some commuting experiences. There are people traveling to new schools or new jobs, perhaps from a new residence. They may be a little unsure about the directions, or about whether that last turn is a left or a right. Give them a little extra room to maneuver.

Here are some of the specific difficulties you may encounter.

Back to school

School opens in Alexandria and in Fairfax and Arlington counties. Some other large systems, including the public schools in the District and in Montgomery and Prince George’s counties, opened in late August.

Watch for young people at the school bus stops and remember to stop for the flashing red lights and signs when the buses are loading and unloading. Note the speed cameras in school zones in Maryland and D.C.

Northwest Branch bridge

Drivers will encounter a new traffic pattern this week at the Capital Beltway bridge over the Northwest Branch in Silver Spring. Three lanes will go to the right of a work zone barrier and the fourth will go to the left of it.

This stretch near the Beltway’s interchange with Interstate 95 is one of the region’s traditional trouble spots — with or without a construction project — and by 7:30 Tuesday morning, the outer loop was congested between I-95 and Georgia Avenue.

HOT lanes construction

Construction workers will be busy on both the Beltway and I-95 in Virginia this fall. The high occupancy toll lanes on the Beltway probably will be open before winter, and many stretches of pavement look done. But the most complicated parts of the project are the interchanges at I-66 and at the Dulles Toll Road, and there’s a lot of work to be done there.

All lanes are scheduled to remain open at rush hours, but drivers should watch for slow-moving construction equipment on the left sides of the inner and outer loops.

The I-95 HOT lanes project just got underway this summer and isn’t scheduled to be done until 2014, but drivers will notice the impact this fall. They may include slower travel times in the High Occupancy Vehicle lanes. Full closings of the HOV lanes may occur from 8 p.m. to 4 a.m. every night, and one lane may be closed until 5 a.m.

Sporting news

The Washington Nationals are at Nationals Park all week. After this, the team has two more home stands in the regular season. But the Nationals are in good shape to generate some traffic and transit news during the post-season in October.

The Redskins will start generating traffic on Sunday, Sept. 23, when they play their first home game at FedEx Field in Landover. The D.C. region’s college football teams will be back in action on Saturday afternoons.

Metro Rush Plus

Metro began its rush hour service realignment on the Blue, Orange and Yellow lines in late June, so September will be the first full month for Rush Plus outside of vacation season.

Blue Line riders have complained all summer that the new rush hour schedule has resulted in more crowded trains. Now that so many people are back at work, we’ll watch this situation carefully.

New SmarTrip rules

Starting this month, Metrorail riders need to have at least $1.20 on their regular SmarTrip cards to enter the stations. The minimum is 35 cents for people using the reduced fare SmarTrip cards for seniors and people with disabilities.

The Metrorail Fast Pass, the one for seven days of unlimited Metrorail travel, now is available for purchase only on SmarTrip. But the old paper Fast Pass cards can be used through Dec. 31.

The rebate program for SmarTrip card purchases took effect this month. People who buy a new SmarTrip card for $5 can get a $3 rebate after they register the card online. The $3 will be credited to the card five days after its first use.

Unfortunately, not all stations have vending machines for SmarTrip card purchases. Although 47 stations do have them, the distribution won’t be complete till November, the transit authority said.

What’s better

I hope Maryland drivers heading to work in the District or Virginia this fall will discover the advantages of the new ramp from southbound D.C. 295 to the 11th Street Bridge. This provides a convenient route to downtown D.C. and to the 14th Street Bridge over the Potomac. The outbound ramp, from the 11th Street Bridge to northbound D.C. 295, is scheduled to open later this year.

Route 50 inside the Beltway looked pretty bad Tuesday morning, and the reconstruction of the New York Avenue bridge over the tracks north of Union Station still has a long way to go. The new 11th Street Bridge ramps could help some of those drivers.

In Virginia, the major breakthrough of the summer was the full opening of the THRU and LOCAL lanes on the Beltway’s outer loop approaching the Woodrow Wilson Bridge. That should make fall traffic a lot easier for both local and long-distance drivers.

Beulah Road bridge

The Virginia Department of Transportation has begun a rehab project on the Beulah Road bridge in Fairfax County.

On Wednesday, Beulah Road will be reduced to a single lane in that area. A temporary signal at the intersection of Browns Mill Road will control traffic until the project is done at the end of the year.

Loudoun bridge reopened

VDOT has reopened Gleedsville Road in Loudoun County, which had been closed to through traffic since June while the bridge over Sycolin Creek was replaced. Some minor work will continue through September.

Metro weekend delays

The transit authority skipped over the major track work planned for the Labor Day weekend to accommodate the crowds at Nationals Park, but Red Line riders should anticipate a big disruption in service this coming weekend. From 10 p.m. Friday through the trains system’s midnight closing on Sunday, free shuttle buses will replace trains between the Dupont Circle and NoMa-Gallaudet University stations.