How many pedestrians are on that sidewalk? That would seem like the best place to put the cyclists, as long as they can be sane around other bridge users.
Also consider making bicycle (bike/pedestrian) specific bridges.
Eugene may be somewhat unique with I think 5 bicycle bridges across the Willamette river, and 2 over the McKenzie river. Plus several smaller bridges. There may well be more bicycle bridges crossing the river than automobile bridges.
The river is smaller than in Boston, but it is also a lot smaller city.
It just seems a little crazy to apparently cut the vehicle access in half, but not spend the money on bicycle infrastructure.