Steel beams will be placed across I-95 South near Garrisonville Road for the southern overpass on the 95 Express Lanes project. (Mike Salmon/VDOT)

[This post has been updated.]

Some drivers heading south from the D.C. area this weekend will encounter delays because of the region’s biggest road work project.

Starting at 9:30 p.m. Friday and Saturday, the Virginia Department of Transportation plans to close lanes on Interstate 95 South from just before Russell Road to Garrisonville Road. From 1 o’clock to 5 o’clock Saturday and Sunday mornings, expect to find all the southbound lanes closed and a detour in effect.

While drivers are detouring, workers will be lifting steel beams for a new bridge to carry traffic from what will become the 95 Express Lanes in the highway median to the right side of I-95 South, just north of Garrisonville Road.

During the set-up hours when the lanes are gradually closing, drivers should expect to encounter travel delays of about 20 minutes. Once all the lanes are closed, southbound traffic will be detoured to Route 1, which parallels I-95.

All the lanes on I-95 should be open by 9 a.m. Saturday and by 10 a.m. Sunday.

Update: Drivers in the northern section of the I-95 construction zone also will be affected by weekend work.The HOV lanes on I-395/95 are scheduled to close from 11 p.m. Friday to 5 a.m. Monday. That will limit weekend drivers to the regular lanes of I-95 between D.C. and Dumfries.

In the next few weeks, workers should complete the last of the steel lifts for the project. That includes the beams for the flyover ramp across I-95 near Garrisonville Road for the one across I-395 near Edsall Road. The entire work zone is 29 miles long, more than double the 14 miles for the Capital Beltway’s 495 Express Lanes project completed last November.

Nine new bridges are being built for the I-95 project, one of the longest road work zones in the nation. While the project is just reaching its mid-point and isn’t scheduled to open for traffic till early 2015, project managers think 2013 will be the most disruptive year for drivers along the corridor, because of the bridge construction and paving underway to create the high-occupancy toll lanes. By late this year, crews will have placed nearly half a million tons of asphalt along the route.

Drivers continue to endure construction disruptions throughout the week, in addition to these special weekend detours for the bridge work. The construction will continue in 2014, with continuing effects on daytime and nighttime traffic. That will include weekend closings of the HOV lanes, some limiting of shoulder access and a lot of slow-moving construction trucks in the work zone.