For years it was one of the most visible construction projects around the District — a massive building rising alongside I-395 in Virginia, brightly lit up at night so that it couldn’t possibly be ignored. But the Mark Center, which has started taking in government workers and contractors, remains a worry for local officials, both in terms of traffic and security.

The Washington Times reports today that Alexandria Mayor Bill Euille penned a letter to President Obama to express his concerns over security at the new Department of Defense building. According to a report in Time last week, the building’s designers seemed to miss one significant vulnerability — that the building sits so close along the freeway. “It is necessary for DOD to be open and honest with the City and its residents so that they can be reassured that there is no lack of security at the [building],” wrote Euille in his letter to Obama.

Another concern is traffic. The building will eventually house 6,400 employees; 2,300 are expected to be in place by this week. According to WJLA, the Mid-Atlantic AAA is warning that area commuters can generally expect more traffic as more government workers travel to new sites as part of the Pentagon’s Base Realignment and Closure (BRAC) process.