Right now, the 71/73 buses go in the south portal from Mount Auburn St to the upper busway, discharge passengers, go out the north portal, loop around the Common, come back in the north portal to the lower busway, pick up passengers (this is where the wrong-side door issue arises) and head out the south portal. The other buses, e.g. the 77, go in the north portal, discharge in the lower busway (also on the wrong side, but it's less of an issue for discharging), loop around the Bennett St garage and come back in to the upper busway to pick up. If you make the busways both run the same way, all buses will have to both discharge and pick up at the same time, and get to or from their routes through the middle of Harvard Square, which kind of defeats the purpose of a busway.