The Red line of Los Angeles is a fairly new Subway System and so is still growing. You now have two lines, both terminating at LATC, Los Angeles Transit Center. Used to be LAUS, Los Angeles Union Station. The trains are quite short during off rush hours but can get to four units, two cars per unit, or eight cars. The stations can easily handle a train of ten cars. The stations are quite long. So far, in every rush hour I ever rode the Red Line, it was a maximum of eight cars. Most likely, as more and more people refuse, or can't afford, to pay the price of a gallon of gasoline, traffic and the number of passengers per train will increase. So far the head way is acceptable, something like 15 minutes between trains. During rush hour that time differential is much less.
In the meantime, it is probably one of the cleanest lines, stations and cars, that I have ever seen. And I used to commute to school with the NYC Subway system. If you dropped something on the station floor there, you would have to clean it after you picked it up.