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the ATL. As congestion increases, the risk that a driver will not clear the intersection within the current cycle increases, along with the delay savings achieved by using the ATL, making it more likely that a driver will choose to use the ATL. This research found a strong correlation between congestion level and use of the ATL. This document presents guidelines that are a culmination of information gathered via a literature review, a survey of transportation practitioners, and an analysis of field data regarding ATLs, along with the research team's experience in the operation and design of signalized intersections. These guidelines are intended to be applied by transportation practitioners as a decision support tool and are intended to supplement national guidance documents and local agency policies and practices on intersection design. SCOPE OF THE GUIDELINES These guidelines apply to auxiliary lanes for through movements that begin upstream of a signalized intersection and end downstream of the intersection. It focuses on ATLs that begin with a right-hand add lane upstream of the signal and end with a right-hand merge downstream of the signal. The operational models presented in these guidelines assume that both the continuous and auxiliary through lanes are free from impedances from left-turn movements and downstream activity. These guidelines provide practitioners with the tools and guidance needed to answer the following questions: What factors affect the use of ATLs? How much traffic is likely to use an ATL? What is the safety performance of ATLs? What tools are available to evaluate operational and safety performance of ATLs? What minimum length is needed for the upstream and downstream components of the ATL? What signs and pavement markings should be applied on ATLs? How can simulation be used to supplement a deterministic analysis of ATLs? LIMITATIONS OF THE GUIDELINES The ATL guidelines do not address the following conditions: Non-signalized intersections Intersections that serve as transitions from either four-lane to two-lane roadways or six-lane to four-lane roadways Left- or right-turn lanes with an upstream addition and downstream drop Approaches that have more than two CTLs Approaches that include shared leftthrough lanes or downstream facilities where queues extend into the ATL Page 2