Reg. rail travel between baltimore and Washington?

What is the shortest distance between batimore and Washington DC by Train. How much time is reqd. for the travel. PL. mention which trains can be taken on this route

Either MARC or Amtrak.

http://www.mtamaryland.com/services/marc/schedulesSystemMaps/marcTrainSystemMap.cfm
http://www.amtrak.com/servlet/ContentServer?pagename=Amtrak/HomePage

Amtrak will take between 35 - 47 minutes depending on what time of day you take the train. The time varies with train services. Train number 2203 is an ACELA and takes 35 minutes from Baltimore-Penn Station to Washington Union Station. Train 143 takes 47 minutes between the same stations.
Check all schedules at:
http://tickets.amtrak.com/itd/amtrak