I have seen sources that cite the broadcast as occurring in Maryland... considering the technology of the day it seemed at first reasonable to assume that most of the broadcast occurred in the New York area. This is not so. The train was the Baltimore & Ohio Railroad. I know for a fact the "pick up points" were Beltsville, M.D. and Laurel, MD. I found a single reference referring to "pick up points." I think these are not regular stop on the train nor are they the locations of repeaters, etc. I think the complete run of the train was from Beltsville to Laurel. This would allow a single site to receive and transmit the program to WABC-AM. The Kane Book of First Facts and Records explains
"The transmitter was operated on a frequency of 1542 kilocycles employing high percentage modulation and running on fifty watts power."
So with only fifty watts ERP at no more than 20 feet HAAT an 8 mile stretch of rail is actually doable. It's journey began in Baltimore and headed north through Maryland, New Jersey and into New York state. Those two towns are only 8 miles apart. There is still a rail line between them, you can see it off to the eastern side of Route 1. These towns are halfway between Baltimore and Washington D.C. about 200 miles South West of New York City. You can actually see the Laurel stop on the map below.If there were two sites to receive and rebroadcast it's possible the program began somewhat before Beltsville and somewhere after Laurel. But I think it is safe to assume that the program in it's entirely was complete before they reached Philadelphia. Belle Baker and Jack Denny's Orchestra were featured on the variety program. The Jack Denny's Orchestra was one of the earliest orchestras on the radio at all. they played on WRC, WJZ, WABC and WEAF. They were in 1932 the house band for the Waldorf Astoria Hotel.