The Army’s decision to move 6,400 defense workers to an Alexandria office complex this year was based on a deeply flawed portrayal of the impact it would have on traffic, according to a report by the Pentagon’s inspector general that is expected out this week.

The Army used bad traffic data to make its case for the transfers and failed to comply with state and federal standards in its proposals to minimize traffic congestion, the inspector general’s report said.

The mass relocation of defense workers to a new building alongside a major freeway in the heart of the nation’s most congested region, a building without immediate access to the Metrorail system, has been controversial from the start.

Northern Virginia’s congressional delegation has united with local elected officials, first in questioning the transfers to the Mark Center complex and then in pleading that they be delayed until road and intersections could be improved.

“This will be the sixth report showing that the Mark Center relocation will create intolerable traffic congestion,” said Rep. James P. Moran (D-Va.). “It’s a damning testament to the Army’s poor planning and the original sin of relocating a facility of this magnitude miles from Metro.”

With fewer than half of the transfers completed in September, the Virginia Department of Transportation found that traffic flow had been reduced to minimal acceptable standards, with morning backups on the Seminary Road exit ramps off Interstate 395, a major artery that carries commuters into Alexandria and the District.

The inspector general’s report is not the first to take issue with the Army’s calculations of the impact thousands of new drivers would have on one of the region’s most congested corridors, but coming from within the Pentagon, it may carry greater weight.

The Army’s written response was as blistering as the report itself, challenging every finding by the inspector general and rejecting each recommendation. The Army said it was cooperating with state and local officials, and providing more than $20 million for traffic improvements.

It said conducting a new traffic study — one that the inspector general said should use more “accurate, reliable” data than the Army’s last effort — would be a pointless exercise that would not “provide additional solutions to past or existing traffic issues.”

“What’s striking is how strongly worded the inspector general’s report is and how strongly the Army responded,” said Ron Kirby, transportation planning director for the Metropolitan Washington Council of Governments. “These are not close views or assessments. They appear to be poles apart.”

Previous conflict

The Pentagon’s inspector general and the Army have jousted before over a 2008 transportation plan that the Army used to justify the transfers. In April, the inspector general said the Army “did not adequately address existing and projected peak hour volumes” in concluding they would have no significant impact on traffic.

The transfers result from the decision of the 2005 Base Realignment and Closure Commission to relocate thousands of Washington-area defense workers, with major expansions at Fort Meade, Fort Belvoir and the National Naval Medical Center in Bethesda.

The Pentagon’s guidelines don’t require that it fund transportation improvements when it transfers thousands of defense personnel unless the changes would cause congestion to double. Calculated as a reasonable standard for bases in relatively rural locations, it seemed nonsensical in a region with the worst congestion in the country. Traffic around the Mark Center probably would reach total gridlock well before its volume doubled.

Planners have said that most of those being transferred to the Mark Center are moving from offices within the region and are unlikely to move to homes closer to their new workplace. Without viable public transportation options, they are expected to drive to work, many of them using I-395, which already carries about 200,000 vehicles a day.

With nearly 5,000 workers scheduled to be in place by year’s end, and the rest arriving early in 2012, commissioning a new traffic study would not alleviate the expected massive congestion.

“If a new, expanded traffic study is performed, it may point out additional regional transit and road improvements necessary to mitigate the impact of Mark Center,” said Tom Fahrney, VDOT’s BRAC coordinator. “However, if all employees are moved as scheduled well before funded road improvements are constructed, our studies indicate severe congestion will develop on I-395, Seminary Road and Beauregard.”

Fahrney said VDOT began warning the Army three years ago that its traffic studies failed to take into account the full scope of the region’s traffic congestion.

‘Need couldn’t be clearer’

T he call was taken up by Northern Virginia’s congressional delegation, which approached then-Defense Secretary Robert M. Gates in January and his successor, Leon E. Panetta, in September. Sens. James Webb and Mark R. Warner and Reps. Moran and Gerald E. Connolly, all Democrats, pleaded unsuccessfully to slow the transfers until road improvements were completed.

“The need couldn’t be clearer for Congress to impose a parking cap limiting the number of cars with access to the site until sufficient transportation upgrades can be completed,” Moran said Wednesday.

Construction on one of the key improvements — a new carpool and bus ramp from I-395 to Seminary Road — was delayed in April when the Federal Highway Administration required a more-thorough environmental impact study. VDOT said the $80 million project would be delayed by 18 months.

Kirby said Virginia officials should reconsider a recently discarded proposal to build high-occupancy toll lanes on I-395 to the 14th Street Bridge that crosses into the District. That plan was dropped after Arlington County brought a lawsuit to block it.

“That would have added an enormous amount of capacity,” Kirby said. “It could have helped get these folks in and out of the Mark Center.”

Virginia Gov. Robert F. McDonnell set up a task force in August to monitor traffic around the Mark Center, warning that arrival of the new workers would “disrupt daily commutes and the movement of goods and freight [and have] wide-reaching impacts that will be felt across the Northern Virginia region.”