https://www.transitchicago.com/travel-information/alert-detail/?AlertId=115377
A 4 car train for any big city is almost a joke. Short trains can full up too quickly. However, a late-night train or an overnight train might be adequate with only 4 cars in a big city.
A 5 car train is better than a 4, but not quite as good as a 6 car train.
https://en.wikipedia.org/wiki/SkyTrain_(Vancouver)#Canada_Line
What should be called, the YVR-Canada_Line wasn't designed to have 5 car trains.
https://en.wikipedia.org/wiki/Canada_Line#Stations The absurd 50 m stations were only designed to eventually accommodate 2.5 car trains. Since 2009, only 2 car trains have be used.
Unlike backwards Vancouver, most major cities have better transportation planning and are on a much larger scale. The Montreal_Metro was built with 500 foot long stations, right from the start.
https://en.wikipedia.org/wiki/Montreal_Metro#Rolling_stock A 9 car train takes up the full 152.5 m platform.
