Large sections of the Silver Spring Transit Center have to be rebuilt because they don't meet safety standards, prolonging the construction-related traffic snarls that have inconvenienced residents for nearly four years.

An engineer discovered that the concrete on the second level of the three-story center -- the planned location of 32 bus bays -- did not meet the standards of either Metro or the American Concrete Institute, said Montgomery County Department of General Services Director David Dise. He said he has no idea when the project will be completed.

Some of the concrete slabs are not thick enough, and some surfaces are not durable enough, explained Metro spokesman Dan Stessel. Metro will not use the $101 million facility until the error is fixed.

In addition to Metrobuses, Montgomery County Ride On, Maryland Transit Administration commuter buses and shuttle buses will use the bus bays. Taxis and kiss-and-ride will available on the top level, while access to Metrorail and MARC trains will be available below.

Though there is no danger that the structure will collapse, the error could mean that the concrete will crack and flake, forcing the county to make repairs earlier than they would otherwise, Dise said. Because the concrete is intended to cover the steel reinforcement bars, or "rebars," cracking could allow moisture to reach the rebars, which would cause additional problems.

The new opening date will depend on the extent of the repairs that are needed, which has not been determined, Dise said. The county may need to replace the entire second floor or much of the steel reinforcements.

The error was made by Facchina Construction, a subcontractor to Foulger-Pratt, the county's general contractor for the project. As a result, the two companies will cover the costs of fixing the error, including the costs of the extended use of crossing guards and police officers around temporary bus stops set up as a result of construction, Dise said.

Foulger-Pratt referred questions to Montgomery County. Facchina representatives could not be reached for comment.

Even if taxpayers are not bearing the financial burden of the delayed construction, area residents still feel the inconvenience of construction delays as they try to get around Silver Spring, said Darian Unger, chairman of the Silver Spring Citizens Advisory Board's Transportation/Pedestrian Safety Committee.

"This is a gateway to Silver Spring, and it's a construction zone," he said. "It delays economic development, there's no question about it, and it interferes with public safety."

The construction has increased traffic in and around the downtown area, said Evan Russell, assistant general manager at 8407 kitchen bar, a restaurant adjacent to the construction site.

"We get a lot of people that ask when it's going to be finished, and we keep pushing the date back," said Russell.

Unger pointed to the years of delays the project has undergone. After initial delays beginning construction, the facility's opening has been previously scheduled for summer 2011, November 2011 and Jan. 7, 2012.

"Residents and commuters both deserve better than this," Unger said.