Crap, bad link and I missed the edit window:
Got it: Steet car line right to Swope Park. It’s te one that runs to the SSE. Oh, and terminates in a large park.
Not to discount your trolley car theory, but as an aside I can’t find any reference anywhere to the Katy Line running through Swope Park, as RAH indicated. Most references I can find vaguely describe it as following the Missouri River. I’m guessing that it’s the line on the map you linked to which does parallel the river, and serves the stockyards on the west side of the city. The line that runs through Swope Park is the St. Louis – San Francisco Line.
Do you really think that a Google Earth view will tell you anything at all about conditions over 100 years ago?
Google Earth seems to be exactly consistent with the historical map that Sicks Ate linked to. It also shows a cluster of enormous manmade structures on the west side of Cairo, Egypt that are in the exact same location that they were 4500 years ago.
The St. Louis – SF Railway also went bankrupt twice. It didn’t regain solvency until 1916 and may not have even been in operation when RAH was five or six years old.
That’s nothing. Sydney Airport used to have a railroad which crossed a runway. From the Sydney Airport Wikipedia page, “On 18 June 1950 a Douglas DC-3 of Ansett Airways taxiing for take-off from Sydney’s now non-existent runway 22 for a night-time passenger flight to Brisbane, hit and partially derailed a coal train travelling on the railway line that crossed the runway. Only the co-pilot was injured.”
Naw, what with continental drift, they actually have moved quite a bit. 
So did Midway in Chicago.
To the OP, Heinlein’s point would have been stronger if he didn’t have to invent his sole example.
Well, that’s just silly.
I hate story problems…