I don't think that transit or subway cars would have been cut into a train for of  freight cars while on their way from the plant to delivery.
They may have been moved as an extra, of 20-30 or so cars at a time and maybe even by night, to avoid potential vandalism along the way.
I've yet to see a photo of transit or subway cars in train movement for delivery, other than at a car float or delivery terminal.
Yet there must have been many such movements over the decades from 1905 to the 1990's, from Pullman, Standard Steel, Pressed Steel, St. Louis, ACF and Budd, to the municipalities buying such rolling stock. I think now such cars are shipped individually on flat cars or on highway flat-bed trailers.

The only movements of transit or subway cars I am familiar with through research, is the delivery of 90 motor units and10 trailers from Standard Steel Car to the Staten Island Rapid Transit (B&O New York Terminal subsidiary) in 1925.
The first ten cars left Standard at Hammond IN via NYC to GE's test track and facility at Erie PA in late February 1925.
These were track tested and had the car controls calibrated by GE to vary switching points between series and parallel.
The cars then went to the SIRT Clifton Shops (sans motors and pickups) along with calibration documentation.
They likely went via Erie to NY and car floats to St. George.
The SIRT Clifton Shops installed the traction motors, shoe beams and contact shoes.

The remainder of the contract was shipped in three additional special movements like the first, going by rail directly to Staten Island via Cranford Junction in NJ.
The attached photo shows the second train of sixteen SIRT cars ready to leave the Standard Steel plant for delivery in May, 1925
In shipping, the cars did not have their traction motors, third rail shoe beams or pickup shoes installed.
An AAR coupler and air hoses were fitted to one end of the first car and the back end of the last for the movement. 
Th remainder of the train retained the Westinghouse H-2A type multiple unit electric couplers.  

Ed Bommer

Virus-free. www.avg.com