U.S. Rep. Jim Moran urged local officials on Wednesday to cement plans for what he called “pretty much an impossible task” — accommodating the 20,000 military personnel slated to move to Fort Belvoir next year.

In a meeting with state transportation officials and Fairfax County supervisors, the Virginia Democrat said they need to have plans in place by March for how to use $150 million allotted to ease traffic concerns expected with the military’s Base Realignment and Closure program.