Wouldnt the "no turn" signs make little difference to traffic passing through, because except for a little street that goes along Spy Pond, everything between the pond and Alewife Brook that crosses the bike path, side streets included, is funneled through one point?

Or did there used to be more crossings in the side streets?

A walk/dont walk signal during rush-hour traffic would improve the situation immensely, provided the pedestrians can be persuaded to wait their turn.