If you are traveling by taxi from BWI, you will likely end up taking a Baltimore taxi. This can be worthwhile if you are traveling in a group, but the distance to DC can make a ride to the district upwards of $75-$100, depending on traffic and conditions. Photo by Mario Roberto Duran Ortiz (CC SA-3.0)
Taxis from Baltimore, MD, home of Baltimore Washington Thurgood Marshall International Airport charge per 1/11th of a mile, at 2.20/mile, plus additional fees (not all of which may be listed here).