Poster "octr202" is correct-Washington, DC used standard gauge while Baltimore had a broad gauge system.
The Baltimore system used a unique 5' 4 1/2" gauge, peculiar to Baltimore. The use of this gauge dates back to the horsecar lines that originated in 1859. Back then, many of Baltimore's streets were paved with cobblestones. This gauge allowed carriages to use the horse car right of way and avoid a bumpy ride.
The Baltimore Streetcar Museum is also unique that, due to the gauge, all of the trolleys in the Baltimore collection were used in that city.
http://www.baltimorestreetcar.org
Pennsylvania "broad gauge" was 2 inches narrower at 5' 2 1/2"-5' 2 1/4" in Philadelphia. This was done to preclude electric lines from hauling steam railroad freight cars on city streets. (If they'd only been able to see into the future and visualize the size of the trucks that now travel in many cities...)
Poster "delvyrails" already mentioned the Los Angeles Railway that used a 3' 6" (42") gauge. Another city that made used of the 42" gauge was Denver-check out this link for a number of photos of Denver equipment:
(WARNING-Lots of photos-may take a long time to download.)
http://davesrailpix.com/dentram/dentram.htm
Currently, San Francisco's Bay Area Rapid Transit (BART) uses a gauge of 5' 6"-the widest gauge ever used in North American transit systems.