This quote is taken straight from NHPR, a site that continually supports commuter rail. The comment that follows is the most succinct explanation of why extending the MBTA to Concord would be unsustainable.
“82,000 people travel from New Hampshire to Massachusetts each day, but only about 2,000 of them take public transit.”
What does that say about transit? It says that transit is a better choice than driving for only two and a half percent of those people. Out of 100 commuters who weigh the advantages and disadvantages of transit versus driving, 97.5 percent of them have concluded that driving is better.
Comprehensive PDF File (not from lobbyists) on commuter rail — and why it would not help to alleviate traffic or pollution, create jobs or improve the economy, draw youth to an area, or be able to sustain itself.