Hillary Hershey sat exasperated in her car, stuck in bumper-to-bumper traffic as she tried to make her way home in the late afternoon rush hour on Wisconsin Avenue in Bethesda. She waved her arms at other motorists, shook her head and pounded her horn, but to no avail.

Traffic tie-ups on Wisconsin routinely test commuters' patience, but construction of a pedestrian underpass at Old Georgetown Road, which began last month, is bringing a new degree of frustration to the daily trek.

"It's terrible through this section, especially with the construction," Hershey said. "And that's anytime of the day except late at night."

The underpass construction near the Bethesda Metro station has made the already congested intersection of Wisconsin and Old Georgetown Road one of the worst in the county, according to Robert McGarry, Montgomery County transportation director. Cars are routinely backed up for two or three blocks, according to county police officer Jane McDonough.

McGarry said the construction has been an inconvenience but the underpass will help alleviate congestion in the area. Part of that congestion was eased by the opening of Metro system in Bethesda in August, but traffic is still heavy, he said.

"If all the people who were taking Metro were driving cars, we'd have a helluva problem," McGarry said.

Construction above ground should be complete in two or three weeks, but the tunnel won't open for 18 months, he said.

The 160-foot underpass, 19 feet below the surface, could accommodate as many as 1,350 pedestrians an hour, according to Robert Merryman, county chief of transportation engineering. The underpass will take pedestrians from the Metro station to the corner of Wisconsin Avenue and East West Highway. Merryman said a temporary steel bridge will enable commuters to use the intersection while work continues below. Pedestrians currently use a crosswalk on Wisconsin Avenue. Merryman said the road will be repaved in October.

The construction crew has periodically closed two lanes and removed the center island to allow traffic in both directions, Merryman said. The steel plates on the road have contributed to the slowdown, according to McGarry.

Meanwhile, commuters in search of relief will have to use Metro, find alternate routes or persevere.

"It's been crazy out here," said construction worker Butch Pounsberry. "I'm out here trying to work and they drive by cussing me while I'm trying to move dirt or something.

"People make it worse on themselves because they're so impatient."

McGarry said residents realize that the county's efforts will improve the situation in the long run, so he said they haven't complained.

"People get delighted to see the road construction, and they're willing to accept it," he said.

Hershey, a 21-year-old from Silver Spring, said she is not delighted. She doesn't see how a pedestrian crossing will solve the problem at what she considers the worst intersection in the Washington metropolitan area.

"I don't think that [pedestrian traffic] is the main problem," she said. "The main problem is just the volume of cars."

McGarrry said that if drivers are unsatisfied with the roads they should take Metro. But Metro isn't convenient for everybody.

Alonzo Weaver, of Forestville, can't take the subway because he gets off work at midnight. Yet he stays away from Wisconsin Avenue on his way to work.

The security guard at the Clark Building on Old Georgetown Road used to leave home at 3 p.m. to start work at 4.

After two months of fighting stoplights, construction and impatient motorists on Wisconsin Avenue, he moved over to Connecticut Avenue, a less direct route but one that cut his travel time in half and also reduced his gasoline costs by $2 a week.

"I'd be at spots on Wisconsin waiting for 10 minutes for cars to squeeze in on one side or the other," he said. "It takes me five minutes coming this way [Connecticut Avenue] and took me 25 minutes to come up here from Wisconsin so I don't even try it anymore, except when I go home. I get off at 12 and it's a straight shot home."