The question of effective utilization of Special Use Lanes (SULs) is often addressed in terms of persons carried, rather than vehicles carried. However, this triggers a more fundamental question, namely what is the underlying upper limit on HOV throughput (or capacity ), given the factors identified in data analysis within this work? Those factors are to a large extent driven by the OD pattern on the facility, which was always known as important but was not accessible enough to be an explicit prevailing condition . The factors that are investigated in this research are: (1) high volumes on the Adjacent Transfer Lane which prevent access to and from the SUL, (2) barrier-separated SUL lanes which may impede access to desired exit ramps, (3) conflicting flow patterns, and (4) hot spots that develop near ramps and SUL access/egress points. The state-of-the-art in SUL research is advanced in this work by (a) studying the effects of the controlling mechanisms on SUL capacity using an extensive data base from Florida and (b) by developing a mathematical model for a facility with a Special Use Lane."