This alternate route from the Merriweather site worked for me for Neil Young show and others for the Killers show... It avoids the snarl at 29 and Broken Land parkway, and you can imagine you are coming from Charm City

The only other option is take the long way around via Frederick and I-70
Alternate route from the Washington DC area:
Take DC Beltway 495 to I-95 North towards Baltimore.
Pass exit 38B, go two more exits.
Exit onto Route 100 West.
Proceed to Route 29 South.
Turn right onto South Entrance Road.
Turn left onto Symphony Woods Road.
Follow to Main Parking Area.