Many people have jumped on the recently released Draft Environmental Impact Report (DEIR) for the Los Angeles Westside Subway extension's comments that the extension was going to have a minimal effect on traffic congestion as justification for stopping the project altogether. But these people are misguided.
First, similarly to freeway expansion, any introduction of additional transportation infrastructure like the subway extension will lead to short term traffic relief, but in the medium and long term the traffic relief will end and congestion will again approach previous levels. We have recently seen this effect with the opening of the long-awaited completion of I-210 in San Bernardino County. Does this necessarily mean that people are not better off? Currently, due to traffic congestion on the westside of LA, people who may wish to travel at 5 PM are now leaving at 3 PM or 7 PM to avoid congestion. When the Westside Subway extension opens, it will draw enough passengers to relieve enough initial congestion so that the above people will now be able to travel at 5 PM. In other words, while congestion may end up being stable, more people will be able to travel at their desired times.
More importantly, projects such as these do not necessarily relieve current congestion, but they allow for more growth to take place in the area without causing additional congestion. For example, in Toronto peak hour traffic volumes on the Don Valley Parkway, one of two expressways serving downtown Toronto, have remained constant since the 1970s despite the rapid intensification of downtown Toronto. Many experts believe the presence of the Toronto subway system is responsible: although there are now many more people working in downtown Toronto than there were 30 - 40 years ago, these people are taking transit to work instead of driving. I expect a similar effect will happen in Los Angeles with the Westside Subway; I wish the DEIR had spent time discussing it.
Finally, the fact that each of the transit projects currently under development in Los Angeles are planned by separate non-overlapping teams in conjunction with federal rules about declarations such as the DEIR makes it incredibly difficult for these documents to discuss the synergistic network effect that will happen with each additional rapid transit line that comes on line in Los Angeles. Each additional line increases the value of the lines already completed by providing more destinations that can conveniently be reached from them. When the Westside Subway extension is completed it will be possible to travel from downtown Long Beach to the UCLA campus in 1.5 hours; it may not sound like much, but currently such a trip on transit takes at least 2 hours and could easily take 3.
I will have more to say about this in the future, but just remember that transit construction is not meant to relieve current congestion; it is meant to give people choices and alleviate increases in congestion.