This is a big weekend for traffic and transit changes in the D.C. region. The District plans to open one of the new spans on the 11th Street Bridge by Sunday, with another to follow in the coming week. Virginia plans to open a flyover ramp at the Capital Beltway/Interstate 66 interchange, easing a long-time traffic misery. Metro is going to change many bus schedules and routes beginning Sunday.

This is the last full weekend for shoppers before Christmas, so expect heavy traffic around the malls and lots of distracted pedestrians carrying packages in the parking areas. The holiday party season also is underway — yet another reason to travel carefully in the afternoons and evenings, and to appreciate the SoberRide program, which begins tonight.

The Capital Weather Gang’s forecast shows a generally pleasant weekend, with daytime temperatures in the 40s. Here are some of the things you need to know about getting around this weekend and beyond.

Metro weekend work

This is the last weekend for scheduled maintenance before the holiday break. Work is scheduled on all five lines from 10 p.m. Friday through the train system’s midnight closing Sunday.

Red Line: The focus of the work is at the Farragut North station, where crews will continue the effort to stabilize a water main that runs through the mezzanine level. Metro is trying to get this work done before an escalator replacement project closes off the south station entrance at nearby Dupont Circle.

To create a safe work zone for the weekend effort, a track will be taken out of service between Dupont Circle and Judiciary Square.

From 9:30 a.m. to 9 p.m. Saturday and Sunday, trains will leave every 10 minutes from the ends of the line at Shady Grove and Glenmont, but every other train from Shady Grove will turn back at Dupont Circle and every other train from Glenmont will turn back at Union Station.

At other times this weekend, the trains will leave the ends of the line every 20 minutes.

The last train from Glenmont will leave 11 minutes earlier than usual, at 2:26 a.m. Saturday and Sunday — that’s the Friday and Saturday night owl service — and at 11:26 p.m. Sunday, when service ends at midnight.

Riders should allow a half hour extra for their travel times and anticipate crowding.

Orange Line: Trains will share a track between East Falls Church and West Falls Church while workers install fiber optic cable.

Trains will leave about every 20 minutes from the ends of the line at Vienna and New Carrollton. Passengers waiting at the stations where the Blue and Orange lines run together should see a train about every 10 minutes.

Blue Line: Trains will share a track between Stadium-Armory and Addison Road and between Reagan National Airport and Braddock Road. All weekend, trains will leave the ends of the line at Franconia-Springfield and Largo Town Center about every 20 minutes. So again, riders waiting at stations where the Blue and Orange lines run together should see a train about every 10 minutes.

Green/Yellow lines: Yellow Line trains will share a track between Reagan National Airport and Braddock Road. The Yellow trains will operate every 20 minutes between Huntington and Mount Vernon Square. They will not continue north to Fort Totten as they normally do on weekends. Board a Green Line train to go north of Mount Vernon Square.

Green Line trains will operate at regular weekend service levels, Metro says. There will be minor adjustments to the schedule, because of single tracking between College Park and Greenbelt for track inspections. Every other train will turn back at College Park during the daytime.

11th Street Bridge

The District is about to open the first two of the three new spans that will replace the 11th Street Bridge over the Anacostia River.

These new spans are designed to carry freeway traffic, and will provide missing connections between Interstates — though not right away. The third span, connecting neighborhoods on either side of the river, is scheduled to be done next winter.

One of the freeway spans, the one that will carry drivers in the direction of downtown D.C., is scheduled to open this weekend. The outbound span will open next week. Mayor Vincent C. Gray is scheduled to host a ribbon-cutting ceremony today, before the first span of this D.C. megaproject opens.

There will be some immediate benefits, but drivers will still have to wait a while for the big breakthrough, the ramps that will connect the Interstates. At first, the two new spans will simply replace the old ones. Traffic must be shifted to create space to complete the new ramps.

Of most immediate concern to drivers will be the lane closings this weekend in preparation for the scheduled opening Sunday of the new inbound span.

The District Department of Transportation will be closing lanes along northbound I-295 to prepare the traffic switch from the old inbound bridge to the new one.

A single lane will be closed between Howard Road SE and 11th Street from midnight tonight to 10 p.m.Saturday. All northbound lanes between Howard Road SE and 11th Street SE will be closed from 10 p.m Saturday till 9 a.m. Sunday, when one northbound lane will be reopened. At 11 a.m., a second northbound lane will be reopened.

The ramps from northbound I-295 and from 13th Street SE to the old inbound bridge will be closed from 9 a.m. to 5 p.m. Sunday. The ramp from the old inbound bridge to the westbound Southeast-Southwest Freeway will be closed from 10 p.m. Saturday till 5 p.m. Sunday.

Watch for detour signs. While the northbound lanes on I-295 are closed, drivers will be detoured via the ramp from northbound I-295 (Exit 4) to the old 11th Street inbound bridge and M Street SE to the eastbound Southeast-Southwest Freeway using the 9th Street SE entrance ramp. From the eastbound freeway, they can reach northbound DC 295 via eastbound Pennsylvania Avenue SE.

While the ramps are closed from northbound I-295 and from 13th Street SE, drivers will be detoured onto South Capitol Street to reach the westbound Southeast-Southwest Freeway, I-395, and M Street SE.

This is a lot of detouring, and congestion is very likely during the closing hours. It would be best to avoid the inbound bridge area entirely till the new span is open.

Beltway/I-66

A new flyover ramp from eastbound I-66 to the inner loop of the Capital Beltway is scheduled to open by 9 a.m. Saturday. From 9 p.m. Friday to 9 a.m. Saturday, crews in this work zone for the high-occupancy toll lanes will close both exits from I-66 east to the inner loop as well as three lanes on the inner loop. Detours will be in place, but it would be best to avoid the area around the interchange because congestion is likely.

The new ramp will do two good things: It will eliminate one of the left-side entrances to the Beltway’s inner loop. That’s a bad spot because of the mix of the slower moving traffic coming off the ramp and the faster moving traffic in the left lanes of the Beltway.

Also, it will create an entrance on the right side of the inner loop that will particularly benefit northbound drivers who want to get off the Beltway at the nearby Route 7 exit into Tysons Corner.

Still, it will take drivers a while to get used to these changes, and the flyover ramp doesn’t eliminate every problem at the interchange. So drivers should use caution and anticipate that congestion will continue near the ramps.

Metrobus changes

Metro continues to adjust bus schedules and routes to improve performance, and there’s a big round of those scheduled to start on Sunday. Dozens of changes will occur on routes across the D.C. region.

A few examples: To reduce crowding on Route D6 (Sibley Hospital-Stadium-Armory), a new weekday trip will leave Stadium-Armory at 8 a.m. heading for P and 22nd streets NW. Schedule adjustments on Route 94 (the Stanton Road Line) are intended to reflect the realities of heavy traffic by scheduling the buses every 12 minutes rather than every 11. Schedules for some off-peak trips will be adjusted by a few minutes to make better connections with Green Line trains, the transit authority said. See the full list of changes on Metro’s Web site.

South Dakota Ave./Riggs Road

The District Department of Transportation’s closing of the right-turn lane on eastbound Riggs Road NE that leads to South Dakota Avenue NE is scheduled to continue for another week.

Access to South Dakota Avenue remains open via the ramp on Riggs Road at the site of this interchange reconstruction project.

Nebraska Avenue project

The District Department of Transportation recently began a year-long reconstruction project on Nebraska Avenue NW. Eastbound Military Road approaching the intersection with Nebraska will be closed to traffic through the winter. Signs trace a detour route using Nevada and Nebraska avenues to carry the eastbound Military Road traffic around the construction zone.

Nebraska Avenue will have at least one lane open in each direction throughout this period. Work hours are 7 a.m. to 7 p.m. weekdays. The traffic on Nebraska can get quite congested in the work zone between Military Road and Connecticut Avenue.

The project includes new curbs and pavement on Nebraska Avenue, Military Road and Broad Branch Road. There will be new traffic signals and accessibility ramps at Nebraska Avenue and Military Road and at Nebraska and Nevada avenues. The sidewalks and storm drains will be repaired. During the project, D.C. Water will complete a valve upgrade on a 48-inch water main.

Holiday SoberRide

As we launch the holiday party season, the SoberRide program is launching its safety campaign. Offered by the Washington Regional Alcohol Program through a network of cab companies, SoberRide will operate from 10 p.m. to 6 a.m. each night from tonight through New Year’s Eve.

Adults in the D.C. region who are at risk of driving while impaired can get a free ride home up to a $30 fare value by calling 800-200-TAXI (8294).

Meanwhile, the D.C. region’s police agencies are marshalling their annual Checkpoint Strikeforce campaign targeting drunk drivers during the holiday season.