This will limit capacity. Few light-rail systems anywhere in the world use trains longer than four cars. Most use between one and four cars per train. This allows more frequent service and more manageable train lengths. Light rail is an awkward way to move people.
Light rail is a very sleek, efficient way to move people.
It is far less awkward than the private automobile or the city bus. Sound Transit, like many typical light-rail lines, will very easily be able to move 100,000 people per day, while Seattle's busiest bus route carries about 15,000. Exactly my point. Unlike a bus, light rail has dedicated lanes that can no longer be used by automobiles. Gee, that will certainly improve congestion.