I don't think it's realistically possible to get rid of any of these highways. Much as Storrow SHOULD go, that's going to be too radical to get widespread support. And by widespread support I mean like 2/3 supermajority to set it in motion.
Improvements:
Storrow
-- Demolish the Bowker Overpass, restore Charlesgate street grid.
-- Reconfigure the Charlesgate interchange further away from the river w/right-hand exit only and minimal-profile ramps to/from Storrow West.
-- Realign under Mass Ave. to lower-profile roadway on the Back St. side, return all the 'no man's land' in the center to the Esplanade. Move Mass Ave. north off-ramp to right-hand exit on re-centered roadway. I guess you could do a Mass Ave. south to Storrow west on-ramp if you wanted with that reclaimed space, but I prefer not inducing any more demand.
Soldiers Field Rd.
-- Reduce to 4 lanes between Western Ave. and Eliot Bridge. There doesn't need to be a continuous frontage lane, and this is dangerous road because people are switching lanes too fast for the sharp curves. Do adequate merge lanes at each exit and re-claim part of the deleted travel lanes as much-needed shoulder. Now you have a saner left travel lane and right local lane setup instead of speeding travel/speeding travel + crazy merging/frontage + crazy merging lanes.
-- Reduce the excessive Eliot Bridge ramps to a lower-profile setup. Why is this a 10-lane split? That's insane for a 4-lane parkway interchanging with a 4-lane bridge at a partial intersection.
Greenough Blvd.
-- Reduce to 2 lanes from Eliot Bridge to Arsenal St. and trade in reclaimed space for bike/pedestrian paths on both sides. This road is ridiculously underutilized for how wide it is, and is a scary proposition for pedestrians with the substandard sidewalks and speeding traffic.
-- Narrow the profile of the Cambridge-side Eliot Bridge interchange. Greenough east doesn't need to split into 2 + 2 lanes, and merge into 3 + 1 lanes. 1 + 1 / 1 + 1. And fix that stupid endless red light from Fresh Pond Pkwy, bar none the dumbest timed traffic signal in Metro Boston. It prohibits all traffic whatsoever onto Greenough west when half of the interchange is on a protected merge. Who does that??? I have never felt so dumb as when sitting at that thing for 5 minutes staring at wide open road while some uptight idiot behind me starts inching forward pressuring me to run the red.
-- Fill in the discontinuity in Greenough at Arsenal. Did this road used to go straight through and then get demolished through that open field long ago? Bizarre layout. Traffic completely hoses Arsenal in both directions with all the people making left turns to/from Greenough next to the Arsenal with no light protection. That's stupid, and this bottleneck is also what keeps Greenough so sorely underutilized throughout. Connect the ends together at one light and abandon the jog behind the Arsenal to parkland. This road could be a new secret weapon for getting around smoothly were it not so oddly laid out.
Memorial Dr.
-- Signal coordination. Especially BU Bridge-Harvard. Traffic flow is incredibly choppy because the signals are all asynchronous. Biggest single improvement they can make to the entire roadway.
-- Eliminate the right-lane parking from JFK Park to Mt. Auburn St. This is senseless for both residents, who have to be home to move their cars at rush hour, and drivers who have no warning that the right travel lane is on-street parking until they have to do frantic weaving. If you're gonna do that, don't stripe the frigging lane...make it a breakdown lane with permitted travel 5 weekday hours per day. I would be terrified to park there lest I be the last car in line when some out-of-towner guns it out of Harvard. If the neighbors need parking, find it somewhere. But not on the freaking parkway.
-- Fix the Doubletree light...you know, the green that's always red? They make these things called turn arrows, guys.
-- Better ped access to the reservation. Eliminating the eastbound parking lane was a good start. Now they have to find some way to make all that parkland in the middle more usable and inviting to people. Think "active lifestyle" Comm Ave. Mall with exercise equipment or something. It's a big patch of green canvas that could be a lot better utilized, and if it's got higher activity that'll bring further traffic-calming effects.
-- Erosion mitigation. That's a sorry, sorry excuse for a "riverbank" from Mass Ave. to BU Bridge. Badly graded sand and geese s***, walkways too narrow to be all that functional. It's beyond me why they've let the deplorable soil conditions persist here when it's probably the #1 source of runoff pollutants in the basin. See above...additional traffic calming if people are actually using the "green" (use your imagination on this one) space.
Pike
-- New staggered ramps in Back Bay to offload Storrow capacity, replace Bowker.
-- Eliminate Allston tolls. I know this is radical, but I'd rather see the lost revenue offset (and them some) by state-line tolls on 93/95/91/US3 than have this continue to be some great wall making it hard to get around the urban core. That monstrously overdesigned interchange was for the I-695 inner belt, not the river roads. It wouldn't be so heinously complex if 695 had been canceled before it was already open.
-- New exit: Birmingham Parkway rotary, Allston. Ties in North Beacon St., Charles River Rd., Nonantum Rd., the other ends of Soldiers Field Rd. and Greenough Blvd., takes a load off Newton Corner by funneling Watertown Sq. traffic onto the light-use river roads, takes a load off Cambridge St. by drawing away Allston traffic that would otherwise have to reverse direction. Contiguous link to the river roads is supporting reason for dropping the tolls, though I suppose if they absolutely HAVE to stay you could do up this one with high-speed tolls + 1 single manual booth per ramp and bring back the Newton exit tolls in tandem for parity. I'd make 'em cheap tolls, though, to encourage local travel.
-- Beacon Park relocation. Been discussed here before, but the viaduct and all of the overpasses are facing end-of-life and potentially hugely expensive rebuild. And odds of Harvard successfully developing Beacon Park after the struggles they had elsewhere are slim the way the Pike shears it off from Lower Allston. As it's an overbuilt I-695 residue interchange and high speed tolls don't require the massive footprint of manual tolls, time to blow this sucker up and go minimalist. Build a new carriageway at-grade on arrow-straight path through the rail yard, inclining up onto the viaduct at Harry Agganis Way. Rehab the viaduct east of there where the tracks have no choice but to run underneath, demolish it west of there where it starts to turn north. Land swap nets Harvard property that's fully facing and integrated with Cambridge St., and probably more total acreage than it's got now hamstrung by ramps.
-- Allston exit Option #1: Construct narrow-profile right-hand flyover ramps for eastbound to/from the exit. Consolidate all the twisting and weaving into narrower profile. New direct ramp to Storrow east (on footprint of that useless truck U-turn lane behind the Doubletree), straighter entrance from Soldiers Field Rd. east frontage road. Somewhat improved intersection with Cambridge St., but mostly same design as now. Direct Storrow east entrance/exit ramps and new Birmingham Pkwy. exit at other end relieve considerable strain on Cambridge St.
-- Allston exit Option #2 (more expensive): Cut Storrow the length of the Doubletree-Western Ave. frontage road so the roller coaster dips are combined at 100% below-grade (easier construction here than elsewhere because of the existing underpasses and frontage roads usable during construction). Deck over the newly cut parkway and re-center the frontage roads on top of it as a 4-lane boulevard to reclaim park space. Construct Pike-to-Storrow east ramp as in Option #1, but create flyover ramp to/from Pike sliding on top of the Doubletree end tunnel portal. At-grade intersections at Cambridge St. and Western Ave. Aligns perfectly with straight traffic onto the underutilized western river roads, consolidates all the Allston and Cambridge movements into straightforward left/right turns, extremely narrow profile and efficient land use, reclaims maximum possible real estate for redevelopment, allows Cambridge St. to be completely flattened at-grade and contiguously redeveloped from Lower Allston to the river (i.e. no bridges, ramps, or landfill hills shearing it off).
Other related
-- Blowing up McGrath Highway and making (improved) Rutherford Ave. and (improved) Mystic Ave. the prevailing traffic pattern from Fellsway to the river roads helps everything immensely by cutting a huge amount of turning traffic out of Leverett Circle and the O'Brien/Memorial intersection. The ramps straight-feeding the Pike to either end of Soldiers Field Rd. does a lot of traffic-balancing to roads in that direction that can handle it and away from roads that can't handle excessive turning and weaving. This serves the same function for the McGrath/O'Brien/Craigie/Leverett clusterfuck. If there's anybody I WANT speeding along the river instead of using the Pike it's the drivers funneled through Charlestown who can pass quietly underneath Leverett Circle or go straight coming off the Gilmore Bridge instead of tying up a turn lane in front of the Museum of Science. Not only is the state not providing enough incentive to do this commute the easy way, it's not providing nearly enough DISINCENTIVE to stop overflowing 28. Which is, after all, supposed to somehow become the friendly main street of the Northpoint and Brickbottom great white hopes...something that's not gonna happen if traffic don't become a lot less intimidating. So I think you have to figure the whole whither McGrath/Sullivan Sq./Rutherford Ave. debates into improving the river roads.
