One way roads work much as they did previously except that now vehicles travel along one-way roads at freeway speeds! Additionally, if you try to change the direction of a one-way road without first erasing the road it will transform the road into a freeway.
If you really want to change the direction of a one-way road, then erase the old road first. Build the new road in the opposite direction after the old one-way road is gone.
Many of the city item exchanges are updated to convert freeway tiles into two one-way tiles. That new exchange allows you to get back any one-way tiles consumed by conversion to freeways.