Nearly five years after the Sept. 11 terrorist attacks and a year after Hurricane Katrina left thousands of people stranded in massive flooding, emergency officials in the Washington area have not identified the people they would need to move to safety in a mass evacuation.

The region doesn’t have a registry of people who would need assistance, but about 35 percent of the District’s households do not have access to a vehicle, said Natalie Jones Best, emergency preparedness and risk manager for the Department of Transportation.