Looking towards Cambridge
Looking towards Boston
My best guess is that it's an attempt to streamline diverted traffic from the Craigie bridge closure, which means it may only be in place for a month while Craigie is closed.
They were anticipating a huge volume of traffic coming off of mem drive and trying to cross into Boston, and they wanted them to be able to merge onto the bridge faster. I don't see that volume of traffic, so it seems like overkill to me, and kind of a mess for bikers. I don't mind the bike lane zig zagging, but there's so much visual clutter, that I'm worried that people entering the lane won't see bikers coming, what with the giant sign, the bollards and so on.
I sent photos to someone who has better contacts at Mass DOT to ask what's going on, but that's my best guess.
Do you ride there? What do you think they should do there? Anything? Or does it seem clear now that you've passed through it a couple of times?