Big different is length of car. PCC could fit 100% on the longest (75') cars then with no overhang. The new car overhang the longest cars in the system that you need idler cars at each end for clearance.How did they ever handle the delivery of THREE PCC streetcars at the same time?
Answer: they did just fine.
The length of a car is from the centre to centre of the coupler and the longest flat is 89'. Therefor you can an overhang and for safety reason, you need extra clearance between different types of cars and that is where idler cars come into play using various length of flat cars. Even if the whole train is our new cars, still need an idler car between them. Don't forget, trains travel around curves and the clearance become tighter doing so. Couplers move in and out of the pocket depending what taking place as well.