My only solution to this would to be constructing a tunnel for thru traffic underneath Storrow Drive. (I know a lot of you are going to say "Dont you remember the big dig?" Yes, I do, but I dont think adding more exits to the pike would be sufficient.) Above, a more narrow Storrow Drive could be constructed, along with bike paths and parks.
"Only solution"?
I mean look, if we're going to consider $10 billion 'solutions' then perhaps it might be wise to first consider cheaper alternatives.
How about putting tolls and charging the market price for using Storrow Drive, based on demand?
Oh yes, I can already anticipate all the objections: "Awww but c'mon, roads are meant to be FREE! You can't charge for freedom! We deserve to sit in traffic!"
Or, "politics will never allow charging for use of Storrow Drive."
I acknowledge politics, but I also acknowledge that it's incredibly irresponsible to ignore alternatives to a massively disruptive environmental nightmare that a full-length tunnel would be. And I think it's fair to put the order of magnitude cost at $10 billion to fully implement such a monster.
P.S. Welcome to archboston!