A roller conveyor includes a plurality of idler rollers positioned along and between opposite sidewalls and a transverse drive system operable to rotatably drive at least some of the idler rollers of the roller conveyer. The transverse drive system includes a motorized roller positioned generally transverse to the idler rollers and a plurality of drive members drivably connected between the motorized roller and respective ones of the idler rollers. Actuation of the motorized roller drives each of the drive members, which in turn independently rotatably drive the respective idler rollers. The transverse drive system may be selectively operable to accumulate articles on one or more zones of the roller conveyor. The roller conveyor may include a right angle transfer unit operable to transfer articles in a direction generally normal to the direction of conveyance of the idler rollers.