Route 991 was a commuter bus route operated by the Maryland Transit Administration in the U.S. state of Maryland between Hagerstown, Frederick, and the Shady Grove Metro Station.The line has since been split into two different routes. The line is operated by the private contactor Eyre Bus Company. Service operates on weekdays only, providing AM service from Hagerstown to Shady Grove, and PM service from Shady Grove to Hagerstown, operating primarily along I-270 and I-70. The buses also operate to Rock Spring Business Park. Two stops are made in Frederick County.