This is more of a 'crazy arterial' pitch rather than a crazy highway pitch. Could we just ban left turns along most of Mass Ave? I was thinking about my last visit to Europe and I recalled seeing a lot of intersections where the signals are simple because they don't allow left turns and require you to make "semi direct" (right before, then left, and left) or "indirect" turns (multiple rights) to make the desired left turn. A lot of Mass Ave seems like a place to try this -- they already do a lot of this in Cambridge around Central Square and MIT. In Boston, at least Back Bay and South End seem like places that should be trying this and even between Porter and Arlington in Cambridge.