here is a link to a helpful paper on the matter written by our (my district's) State Rep, Denise Provost. I don't think it directly answers your question, but it gives some excellent background and good information. She's really hot on the topic, so is a good resource.

It's a .doc, so if that poses a problem, I can copy and paste the content somewhere.

http://www.deniseprovost.org/images/Testimony/1.25.12%20op-ed%20mbta.doc