I read this article about managing pedestrian street crossing in the Boston Globe today. It's a pretty good article. I like that people are finally starting to realize that it's a losing game to try and make a city be as efficient as possible for cars to the exclusion of pedestrians, buses, bikes, etc.
But there's a gigantic element missing from this article: namely, the elements. Can we stop living in denial that the weather in Boston just plain sucks? It always sucks. It always WILL suck. For at least four solid months of every year, there will be snow on the ground that you can measure in feet. For three months beyond that, you can count on frigid, hurricane-force winds...like as not with driving rain. And for good measure, don't forget July and August when it's typically hot as hell and humid to match.
So if you really want to improve the pedestrian experience in Boston, don't make people walk on the street at all. Make them walk above it, or below it. I'm talking about a system like the Minneapolis Skyway, the Montreal Underground City, or any one of a dozen other systems across the globe. A system of walkways and public areas that are in fully-enclosed spaces.
Boston already has a small version of this in the connecting walkways between the Prudential Mall, the Copley Mall, and the Westin Hotel. It's a very handy and pleasant way to walk about five or six blocks in total comfort. Similarly, the system of tunnels under MIT's campus, (PDF) while inherently limited to just serving the MIT area, is also very handy during the winter.
And it's also has the potential to be a prime driver of commerce. Not so much in a true "mall" sense, but you could easily have lots of little news-stand and Dunkin' Donuts kiosks (perfect for commuting times) and some CVS's sprinkled around. Maybe even some mini-supermarkets so you could shop for your dinner ingredients on your way home.
I don't deny this is would not be an inexpensive system to implement. But I would argue that it's probably less expensive than many would think. There's a tremendous amount of public interior space in many buildings that is poorly leveraged at the moment, but could be (relatively easily) connected via a skywalk. Or just renovate the miles of tunnels under Boston that are often just sitting abandoned at the moment.
These tunnels wouldn't even necessarily have to be open 24/7, either. Minneapolis's is not and it works fine. All they have to be is well-lit, well-ventilated (but not open-air) and reasonably clean, and people will use them in droves.