The Maryland Transit Administration is keeping its bus routes rolling, but in many cases, it has modified routes as a concession to the snow. Here's the damages, straight from the MTA:

10:00am latest update:

MARC Train is operating on S schedule and experiencing 10-20 minute delays.
Metro and Light Rail are on schedule.

The following diversions are posted on the website.  A link was put on the Special Announcements section.
No. 1 Terminates at Mondawmin.
No. 5 Bus by-passing Park ave.
No. 9  Bus terminate at  Ridgley and Cranbrook.
No. 13 Bus by-passing Edgewood, staying on Dennison.
No. 15 Bus terminates at Walbrook Junction. West bound left at Guildford, right at Fayette, right at Park, left at Saratoga. Will service White Marsh Mall.
No. 16 Bus by-passing Violet Ville and Brooklyn area.
No. 20 Bus is by-passing St. Agnes Hospital, and Culver and Monastery
 
No. 22 Bus terminates at Eastern &  Ponca – bypass Bay view.
No. 23 Bus  by-passing Wildwood Parkway
No. 23 and 40 use Lombard to Ponca to Eastern in both directions.
Nos. 27, 29, and 51 Buses are staying on Cherry Hill Road
Nos. 10, 35, 33 and 27 pulled off the street.
No. 36 Bus  by-passing Argonne Drive, staying on the Alameda
No. 40 WB will terminate at Edmondson Village, not servicing Rt 40 & Rolling Rd.
No. 44 Bus WB from Rosedale will terminate at Northern Parkway @ York.  EB from Security will terminate at Sinai.
***All services will by-pass the Bay view Medical Center***