You can't cross on the Tobin or on I93.
But on the map you can see Alford St (99), Main St (Medford) (38) and River St/Harvard Ave. Just off the map is Medford St/High St (60) double rotary. After that it is no longer a river.
So that leaves out Boston Ave, Main St (Somerville), Winthrop St, Fellsway, and the multiple Mystic Valley Parkway (16) Crossings.
Contrast with the Charles all the way out to Waltham, where I have crossed every bridge except Arsenal and Moody.
-mr. bill