Serena - any roadstuff is good stuff, you should know that
As for this project, I've read (small) amounts of info on it - as you've said, it's to increase capacity on the insanely congested Central Artery - only Route 3 (North, IIRC) andInterstate 95are as busy.
However, do not be suprised at this scheme to put elevated roads underground- America's road projects in the 50/60s all involved elevated roads being cramped through spaces wherever possible, they'd run these aerial roads through back-alleys, along water fronts, over houses, etc. Sadly, most were well opposed - and two in San Francisco were demolished (and replaced withwider surface streets). These were the I-480 Embarcadero and the I-880 Cypress Viaduct. Both were two-tier freeways, the former along the bay (blocking the view for thousands of residents) and the latter over a street. Tragically, the Cypress Structure collapsed in the 1989 earthquake, killing 42 people, and the Embarcadero was condemned (but it was a hated road anyway).
New York's elevated roads don't fare much better - I have a friend in New York who drives on the FDR Drive everyday, being stuck in traffic - however, when he visited London he said (and I quote): "I have never been on such a busy road as the M4 and M25near Heathrow Airport. Not even the FDR Drive compares to that area".
I also showed a friend who lives in Rhode Island a photo of traffic on the M25, and he too was shocked - even though he lives near I-95 (which is one of America's largest car-parks apparentally).
Also, when I was talking to them the other night about US/UK road differences (in the middle of explaining the lingo we use - dual carriageway is not a term the US uses, it seems), we established that despite our roads being more technologically advanced, theirs carry more traffic, often on the same number of lanes, yet theydon't suffer the same congestion as we do.
Somewhere we in Britianmessed up - particulary with inner-city roads, London may have looked terrible with the Box running around it, but with careful planning it could've integrated with the scenery.
Sorry to drift off on a tangent - it'sjust that American roads(from whatI've read/seen photos of) are so much better than ours in most aspects...and they're not afraidto spend billions on vital projects, unlike here.