It is not one way - River is one way, and Congress is one way east of River, but it is two-way west of River (coming up the hill, where they must turn right to go over the bridge).

This may be more a matter of confusion - drivers don't seem to notice that it is two-way on the other side of River.

It is legal to "turn left on right" from a 1-way street (Congress Street westbound) to another 1-way street (River Street southbound). Care should be taken when making this turn, besides there is not much traffic on Congress Street coming from Front Street. Keep traffic moving safely and save gas !!!!