Quote:
... Interurban railways often operated two or more cars coupled as a train on busier routes or lines ...
To get some perspective, I consulted (flipped thru) Ray D Applegate's
Trolleys and Street Cars on American Picture Postcards, a lovely book with '191 Reproductions, Including 16 in Full Color'.
There was no point doing an exact count, as a single postcard might come from an operator with >500 cars, or less than 5, and a weighted average would have been unreliable, too.
Some of the cards did, indeed, show multiple coupled trolley cars and, indeed, they were usually on interurban lines.
But the vast majority of cards did not show an obvious coupler on the front of the car, which would have come into use when it was the second (or later) car in a train.
Many of the cars had cattle guards (!) and, of course, there could have been a coupler that was exposed once the guard was dismounted.
More likely, the times were just different. Today, people have become more expensive, and things have become cheaper, so we would expect every car to come with an integrated factory-installed coupler at either end of the car. Back then, things were more expensive and people were less expensive, so it might have made more sense to mount a coupler on a car only when the need arose.
The book (used, softcover) is available for less than U$D 4 ppd to USA at:
http://www.abebooks.com/products/is.../13108204612Cheers,
/s/ ikeyPikey