Having a car in Washington is usually not necessary. While the city is laid out in a basic grid system, one way streets, 4 quadrants that create 4 different "M" streets and avenue's that cross the grid on angles mean the city can be quite confusing to navigate. In addition, parking, especially in the downtown area is very difficult with limited metered parking and expensive private parking garages. We strongly encourage visitors to use the excellent public transportation system to reach your sightseeing destinations.
If you are driving to Washington D.C., please be sure to check the specific parking options of your rental property. Some are able to offer reserved off street parking, usually for an additional fee. Others offer a complimentary street parking pass, that allows you to park on the street like a resident, in the specific neighborhood where the vacation rental is located. Note, the parking pass does not guarantee a specific spot and you are still required to obey posted parking restrictions.
Consider as well, that if you need a car just for one day of your visit, most of the larger rental companies have locations in the city or easily reachable Reagan National Airport. If you are a member of Zip Car, there are car pick up points throughout the city.
These links may be helpful: