Jeff "Pantograph Trolleypole" Wood has a post questioning the value of building new commuter rail lines, as contrasted with light rail or streetcars. He points to several new lines where ridership is well below expectations, and argues that such tiny numbers do little to further our goals.
It has always been acknowledged that these new commuter rail lines are oriented towards relatively affluent park-and-ride commuters, so they won't increase access for underserved communities. The claim was that they would get people out of their cars for at least a portion of the trip, leading to greater efficiency and less pollution and carnage. In addition, some people claimed (or at least hoped) that they would attract relatively well-connected passengers, who in turn would have an interest in lobbying for the maintenance and expansion of the transit system. Jeff argues that such small numbers do very little to help us reach any of those goals.
Everyone seems to agree that these commuter lines are a miserable failure, but there is disagreement over why exactly they failed, and how to avoid failures like this in the future. Jeff takes a technical approach, saying that the problem is that the lines tend to be located in old freight rights-of-way far from residential, job and shopping centers and served by large park-and-ride lots. Significantly, these lines all tend to be relatively low frequency, sometimes only a few trains a day. He recommends that agencies pursue light rail through urban areas instead, and contrasts the ridership numbers on these commuter rail lines with numbers from new light rail lines.
Yonah Freemark expands on Jeff's post, but argues instead that the problem is a political failure, due to a futile attempt to distribute funding across metropolitan regions, hamstrung by bad zoning.
I think they're both confusing correlation with causation. Both of their explanations are probably true to some degree, but in fact only one could, or none; we don't know. There's another factor at work that I think plays a role. I don't have any proof, only a similar causation, but that is enough to require more support for Jeff and Yonah's claims. Both bloggers are suffering from transportation myopia, because for every one of the commuter rail lines that Jeff lists, there was a major road project that improved car travel and took riders away from the commuter rail lines.
Now I know some of the readers are going to jump in and say, "but that highway project outside of Portland is only one lane in one direction for a few blocks!" Yes, but there are numerous other highway expansion projects going on in the area. You can quibble with the details, but I think you'll agree that the overall picture is sound.
If you regularly commute from Maple Grove to downtown Minneapolis and keep getting stuck in traffic jams on I-94, you might consider switching to the Northstar trains. But then if MnDOT adds a lane to I-94 and traffic moves smoother, you might stay in your car. This is partly a failure of commuter rail, partly a failure of regionalism, but mostly a failure of transit advocates to realize how much of a threat competing road projects can be to the train lines they so desperately want to see.