During the period 1987 through 1996, I leased track space from MMID to store my private car ST REGIS RIVER in their yard at Union Bridge MD. MMID operated their own passenger excursion trains until around 1990, when they sold the rights to all passenger service on the line to The EnterTrainment Line. At least twice a year, I would pay them to haul my car on the passenger excursion train from Union Bridge to Blue Ridge Summit / Highfield and return. I always did a fall foliage trip; I tried to do one or two other trips each year. I got as far east as Emory Grove with the car, but never got ST REGIS RIVER on the MMID's Taneytown - Walkersville line.
I especially liked the climb of the 1.9% grade from Thurmont to Blue Ridge Summit. I can remember one year we had three MMID Geeps on the head end pulling 13 cars up the Catoctin Mountains. ST REGIS RIVER was right behind the power on the trip up the mountains ... you could stand in the vestibule and really hear the engines working to haul 13 passenger cars up the grade. I always liked crossing the two trestles not too far northwest of Thurmont, the open plateau with the siding (or remains of one) about halfway up the mountain, the horeseshoe curve at Sabillasville and the former WM station at Blue Ridge Summit which was now the local library. In Professor Potter's biography of Fleet Admiral William F. "Bull" Halsey USN, there is a mention of a young Halsey riding the WM passenger train to visit a friend or relative in Blue Ridge Summit.
I made that trip many other times in business car CATOCTIN, or either working on the excursion train or riding it as a guest. If not riding in my own car, my favorite alternatives were on the open platform of CATOCTIN, in the dome of the former UP/AutoTrain dome diner, in the EnterTrainment Line's open air sightseer lounge car (converted from the fire damaged dining car section of a C&O twin unit diner), or from the open dutch door of any car. Pleasing scenery and a well maintained railroad.
Regular passenger excursions on MMID ended in about 1994 or 1995 when The EnterTrainment Line ceased operations. Their equipment was sold at auction and dispersed across the country. Not long after that, MMID gave notice that they intended to terminate my storage lease, so I moved ST REGIS RIVER to a new home. I have not been back to the MMID since that time, but I have many pleasant memories of those years, thanks to MMID General Manager Alan Novotny and EnterTrainment Line CEO Gus Novotny (no - they are not related).
Here is my photo of MMID dome diner 58 crossing one of the two trestles on the east slope of the Catoctin Mountains between Thurmont and Sabillasville around 1990.