Named Merchandise Boxcars - Where did they go?

I suspect it was the same for other railroads as well, but I can only speak for the PRR.  Merchandise Service cars were not interchanged with other railroads for the duration of special less than carload and expedited merchandise service on the railroad. 

On the PRR, Merchandise Service began in 1946 and ended in 1961, although TrucTrain (trailers on flat cars) service began in 1956 and siphoned off a lot of expedited freight.  When no longer needed for the special service, the cars were returned to general service (still painted with the Merchandise Service band) and were interchanged like any other PRR boxcar.

MoPac were restricted to MoPac and T&P rails.

Initially the NYC Pacemaker box cars were kept on line in captive service to Manhattan's Westside Terminal. They had a restricted capacity of 25 tons for high-speed running.  Also they originally had minimal data marking, which did not meet interchange requirements.

In time they too went out on interchange, had capacity increased to 50s ton and got full data markings. Report marks and data originally in white was changed to black with full data measurements for interchange use.

B&O's colorful Sentinel and Time Saver box car were basically for advertising B&O through freight  services, which included car tracking (Sentinel) and over the road timing (Time Saver) for shippers. The specially painted cars were used for interchange as well as in LCL (less than carload) merchandise service.  However, any other B&O box car,  if clean and weather tight,  would also be used the same way. Most qualifying box cars carried a 'Circle T' emblem on their CAPY line to indicate fitness for such work.  

I'm not as certain about the PRR. However, they did use specially marked cars between certain terminals on regular runs, often being sealed cars loaded with mail.

S. Islander

NYC Pacemaker cars initially were restricted to online service. They ran in groups on specific trains . Later on these cars were interchanged and had the appropriate reporting marks added. The NYC had large online warehouse facilities that allowed partial contents of a car to be transferred to other cars that wre in on line only service and also cars that were being interchanged. 

nkp4me posted:

Just a curiosity question as I continue to organize my freight cars. Would the name merchandise service cars have stayed exclusively on home rails, or would they have gone on other line's rails? Would these have been just in an online assigned service? For instance, New York Central Pacemaker or Early Bird service cars - would they have stayed exclusively on NYC rails or would they have seen service on say, Pennsylvania or B&O?  

Early Bird was not a dedicated service.  It was simply a sales department name for a set of faster freight train schedules between the east coast and western gateways.  The logo was painted on some ordinary box cars.

Good question and interesting responses!