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3. OPERATIONAL ANALYSIS This chapter presents the operational guidelines for evaluating ATLs at signalized intersections. It is founded on a method to predict the volume of traffic that will use an ATL. In addition to evaluating ATL and intersection performance, the results from the operational analysis are needed to determine the recommended minimum design lengths for the upstream and downstream ATL described in Chapter 5. This method supplements the Highway Capacity Manual 2010 (2) procedures. The HCM 2010 does not directly account for the effects of short lane additions (including ATLs) in its lane utilization factor fLU. Instead, it directs users to apply a simulation tool to predict the through-movement volume in the short lane. While some ATL characteristics can be modeled through micro- simulation, the models presented here are based primarily on empirical observations taken at a number of existing signalized ATL approaches across the United States. A detailed discussion of how microsimulation may be used to evaluate ATL performance is provided in Appendix A. Appendix B describes the computational engine that incorporates the ATL lane use prediction model presented in this chapter. Given its unique operating characteristics and lower utilization, an ATL should always be treated as a separate lane group, regardless of whether the lane is shared with right turns or is exclusive. Thus, an approach that consists of a separate left-turn lane, one CTL, one ATL, and one exclusive right-turn lane would have four lane groups as shown in Exhibit 3-1. Exhibit 3-1 Exclusive ATL Lane Group Diagram While the HCM 2010 treats a shared through-right lane as a separate lane group (which is different from how the HCM 2000 lane groups were designated), it still combines all exclusive through lanes into a single lane group. This process is not appropriate in the presence of an ATL because the lane utilization of the ATL is much lower than that of a traditional CTL. This chapter presents the following information: Principles of ATL operations Data collection required for analysis Analysis techniques for ATL operations Page 15