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Firm Overview 

SL Engineering, LLC is led by Susan Langdon, PE, PTOE and is focused on providing high-quality traffic engineering operations and intelligent transportation solutions to clients. Ms. Langdon has been an industry leader in traffic signal operations and ITS applications providing innovative solutions to her clients for more than 30 years. She was one of the first to implement transit signal priority timing providing transit priority within a coordinated signal system in a highly complex urban environment. She further was one of the first engineers to bring Automated Traffic Signal Performance Measures approach to signal operations to the State of Texas and other agencies in the United States. Her decades of experience include traffic signal design and operations, signal systems timing and implementation, traffic systems modeling and simulation, transit priority applications, Automated Traffic Signal Performance Measures and Intelligent Transportation Systems applications. Her experience includes ten years in the public sector with the Wisconsin Department of Transportation and the remainder of her career has been in private practice.

Susan has served in consulting roles with several firms, progressively moving into positions with more responsibility eventually this progression led to the decision to operate her own traffic engineering firm for 8 years, which resulted in a strategic acquisition by an international professional services company where Ms. Langdon served as Principal of Transportation Services for the central US and led the ITS practice nationwide. She is now owner and sole employee of SL Engineering, LLC where she brings her extensive traffic signal operations expertise to clients throughout the US. Susan has developed signal timing for more than 4,000 traffic signals and developed signal plans for more than 450 signalized intersections. Susan has completed engineering projects throughout the US and has led traffic and ITS design for many high-profile projects in Texas, including design-build projects LBJ Express and SH 288; as well as major light rail project Houston Metro; and transit signal priority in the Dallas Transit Mall. She has also served as expert resource in the field of traffic signal operations, most notably, serving on the project review panel for both the Signal Timing Manual and the Signal Timing Manual Second Edition. Ms. Langdon has been involved as a peer reviewer from the initial research on signal performance measures conducted through the TRB Traffic Signal Systems all the way through implementation of Automated Traffic Signal Performance Measures.

Ms. Langdon has also volunteered her time with professional organizations throughout her career such as the Institute of Transportation Engineers, American Society of Civil Engineers, American Council of Engineering Companies and Transportation Research Board. She is Past President for the Texas District of ITE and Past Chair of the Transportation Research Board Traffic Signal Systems Committee. In the March, 2020 edition of the ITE Journal, ITE International President Randy McCourt identified Susan as one of the 12 lions in the industry who have advanced traffic signals.