The Expo Line is couple of miles south of the Wilshire Corridor, so they don't really duplicate each other. Only when and if the Subway gets to WLA and Santa Monica do they begin to compete for some passengers. Some folks don't feel the cost of the Subway is worth it past UCLA, and in any case the subway won't even be able to break ground for 5 years, at the earliest. By the time it actually gets to UCLA-10 or 15 years, then that decision will be made.

Several years ago some folks from the Volpe Center (Transportation "Think Tank") did a study in the LA region on our Computerized Freeway Detection systems, that we put on the internet and into PDA's. All of our freeways have a vast network of congestion detection, available on the web, and web enabled devices, in real time, including accident locations. So you can see in advance how crappy traffic is before you leave, or even enroute.

These folks, being from Boston, figured that commuters and travelers would detect traffic congestion on say the I-10 and divert to what looked like "on the map" an excellent set of "parallel" routes like the 60, 91, or the 210. What they didn't realize until they got here is the sheer size of those corridors,(30X60 miles) and the volume of congestion (they all pretty much suck no matter what) in the "LA Region".

What they found was that a surprising number of people used the information to actually switch business trips to Downtown or Orange County to the commuter rail, where that option existed.
The largest proportion of people using the information changed the time of travel, and others cancelled their trips in response to severe congestion or sigalerts. It turned out almost nobody switched routes, because the probability of equal congestion and the extra distance of these "parallel" routes wiped out any liklehood of time savings.

The "big enchillada" ain't "itty bitty" Boston. The urbanized portion of Southern California is larger than the State of Connecticut. So while these two rail lines are parallel, they're not really that close, either.