i lived in fitchburg for a while and i can tell you the transit to and from boston sucks. route 2 is a nightmare any time of day but way better than the train. I lived with in a 10 minute walk of the commuter rail stop but would never use it because it was faster to drive into alewife. any sort of upgrade on the rail is great in my book, the extension i can take or leave, but if it makes the train more reliable i am for it.
I live off Fresh Pond Parkway and believe me---, I feel your pain. The streets in Cambridge cannot handle the volume of traffic. In the Morning/Afternoon the traffic here is crazy since Route 2 turns into a bottleneck with all the traffic lights in Cambridge. If they have money to burn, they should look at extending a better Northwest corridor in-to/out-of Boston.
I've thought about one.... It may even help your commute depending on the parts of city you goto. It would involve pushing the Fitchburg Line (near Alewife) underground ... From the overpass spanning the Fitchburg Line it can be observed there are four tracks that pass below the Alewife Brook Parkway bridge. There are the two main tracks of the Fitchburg Line, plus a siding of the Watertown Branch Railroad, and one going to a maintenance facility (shed) on the west side of the same Bridge.
I contend, that there appears to be enough land area to build a state-highway above the Fitchberg Line leading directly into Boston. (Since those tracks terminate near North Station).
It could terminate close to McGrath Highway in Somerville or even closer to the Boston Museum of Science area.
It looks to me to be as-wide as Route 9 around Wellesley/Framingham (and it is well known how much volume that route handles daily.)
The route could be a limited access road in order to keep traffic flowing quickly into/out of Boston. (Similar to the access road built between the southeast Expressway and the Ted Williams Tunnel.) and according to MBTA, from Waverly (Belmont) to North Station is 17 minutes. The junction I'm referring is probably about 7 minutes further east so one can easily do that math. I tell you one thing, it would work wonders to keep traffic flowing a lot faster from Route 2.... But that is at least a 3-4 mile long tunnel we'd be talking that would need to be built to put the Fitchburg Line underground between Alewife and Boston. this would open up a final Northwest corridor into/out-of Boston.