Reader Inquiry: Ridership on AC Transit’s Transbay O Route. I noticed that someone has hit this site a few times, searching for ridership information on AC Transit’s O route, which is the transbay route that largely runs on the Alameda portion of the 51/851 route. This is a question that before now has remained unanswered on this site, but I figured that I might as well answer it, since someone appears to be interested: in 2007, daily ridership on the O was estimated to be 1,343. The top-two performing AC Transit routes were the 1/1R (at 21,554 daily passengers) and the 51 (at 18,747 passengers). 72/72R/72M clocked in at 15,019 daily passengers. Interested in the 2007 ridership estimates for other AC Transit lines? Check out the last few pages of this PDF.