A warning to anyone who slogs through the mind-numbing traffic in lower Montgomery County: Things are about to get uglier.

Beginning in a few weeks, key parts of Rockville Pike and Connecticut Avenue just inside the Capital Beltway in Bethesda and North Chevy Chase will be ripped up in what transportation officials describe as a major construction zone for three years.

Think Rockville Pike backs up now? Picture orange barrels shrinking its six lanes to two or four during periodic lane closures.

Officials say the work — mostly adding turn lanes and short segments of lanes to move traffic through intersections more quickly — will help the area accommodate new traffic from the recently expanded Walter Reed National Military Medical Center. The hospital added 2,500 employees, and patient visits are projected to jump from 500,000 to 1 million annually.

“It’ll be a mess,” said Phil Alperson, a Montgomery official who oversees local impact from the military hospital’s expansion.

Construction is expected to begin on Rockville Pike early next month and at Connecticut Avenue and Jones Bridge Road in late March.

The area is a considerable choke point because it encompasses major commuter routes into the District, downtown Bethesda, the National Institutes of Health and Walter Reed. Other roads that will be affected — Cedar Lane and Jones Bridge Road — serve Kensington and Silver Spring.

With about 70,000 vehicles already jamming Connecticut Avenue and Rockville Pike daily, highway officials are warning motorists to expect delays. All lanes will remain open in the peak direction during the morning and afternoon rush, officials said.

Drivers traveling through the area during non-peak hours “are going to be dealing with added delays; that’s a fact,” said Christina Minkler, a Maryland State Highway Administration project manager. “It’s a short-term pain to get the gain in the long term.”

Alperson and local business leaders say they lobbied hard for the improvements to keep traffic moving long-term.

Even as the roadwork is underway, county officials will begin a major two-year tunneling project beneath Rockville Pike starting in fall 2013. That will include excavating a 120-foot deep shaft for a new set of high-speed elevators on the east side of Rockville Pike near the military hospital entrance and a 20-foot-deep pedestrian tunnel.

Both projects are designed to allow people to walk between the hospital campus, the Medical Center Metrorail station and nearby bus stops without having to cross busy Rockville Pike. The number of pedestrian crossings there was projected to jump from 3,000 to 7,000 daily after Walter Reed’s expansion, Alperson said.

Defense Secretary Leon Panetta salutes as he gets the ceremonial scissors fromMarine Corps Lance Cpl. Kyle Carpenter to cut the ribbon at the dedication ceremony at the Walter Reed National Military Medical Center in Bethesda on Nov. 10. (JONATHAN ERNST/Reuters)

NIH officials said they’ve been trying to prepare their 18,000 employees and 7,000 or so daily visitors for the roadwork. Tom Hayden, who oversees transportation issues for NIH, said employees are being encouraged to take public transit, join a carpool and telework. He said NIH officials are concerned that traffic trying to avoid construction on Rockville Pike will clog Old Georgetown Road and the campus’s western entrances.

“We just want to make sure we’re not adding to the congestion,” Hayden said.

The $68 million combined construction costs for the elevators and pedestrian tunnel will be covered with federal money, Alperson said. The state is covering about $30 million of the road improvements, while the federal government will pay for about $59 million, he said.

Rockville Pike will probably see orange barrels first, when crews begin moving underground utility lines between the Beltway and Jones Bridge Road in a few weeks. That utility work will take about a year, highway officials said, and will be followed by another two years of construction to add lanes at the intersections with Cedar Lane and Jones Bridge Road.

Later this year, workers will carve out a longer queue area for southbound Rockville Pike traffic waiting to turn left onto eastbound Jones Bridge. They also will add signs at that intersection to make one of Rockville Pike’s southbound through lanes a second left-turn-only lane during the afternoon rush.

At Connecticut Avenue and Jones Bridge Road, workers will add a right-turn-only lane on southbound Connecticut to carry traffic that exits the Beltway to head west on Jones Bridge while heading to NIH, Walter Reed and downtown Bethesda.

Part of the Connecticut Avenue median will be carved out to create an additional northbound through lane between Manor Road and the Beltway.

The plan also includes construction of a third left-turn lane from eastbound Jones Bridge to northbound Connecticut, highway officials said, but no schedule for that has been set.