If you are in the DC suburbs, either MD or VA, you are better off calling a cab. Any restaurant will call one for you and you will get better service from the restaurant than a direct call. In Arlington/Alexandria, you can expect no more than 5-10 mins for a cab, so you should be pretty close to ready to depart when you call. Even in DC, if you are, as you say outskirts, cabs can be a tough find. Again, have the hotel order one for you unless you see a cab line at the hotel. Different rate systems in DC, VA and MD, but on typical ride, the meter averages out pretty much the same.