Trains and scalability

What with the high gas prices, it's not surprising that even in LA, public transit ridership has been setting records this year. What's particularly interesting about this latest set of numbers, though, is that the Gold Line's ridership has finally exceeded that of the Orange Line busway, and the Orange Line's growth is starting to stagnate. There's a very simple explanation: the Orange Line has basically reached capacity, since it's going to be hard to maintain reliable service with headways closer than four minutes. On the Gold Line, they've gone from 12 minute peak headways down to 7.5. Plus, thanks to the ability to couple trains, as well as the higher speed that comes with proper grade crossing protection, the Gold Line requires 11 drivers to operate peak service, while the Orange Line requires about 24, for a roughly comparable number of passenger miles.
And the Gold Line has quite a bright future ahead of it, as higher ridership leads to a more frequent and thus more attractive service. The Eastside extension can only help matters, by linking more destinations with the rail network. With some upgrades to the power system, they will be able to start running three car trains and boost capacity by another 50% with no extra drivers, and I suspect that headways as close as 5 minutes are possible as well, more than doubling the line's capacity.
Meanwhile, the Orange Line is already running a bus every four minutes at peak, and it's not likely that service can increase much beyond that without creating jams at the many grade crossing on the line. So the buses will get increasingly crowded until an equilibrium is reached between people needing to get somewhere, and people not wanting to put up with the crowding. Or until the line is rebuilt as light rail.