The City of Philadelphia, in an effort to improve the flow of traffic along major corridors, embarked on a comprehensive study of its existing traffic signal system in order to optimize the traffic signal timing of those select corridors. With limited ability to add physical capacity along these corridors due to development abutting most of the corridors, as well as limited budgets, signal retiming remains as one of the most cost effective ways to improve traffic flow, increase capacity, and reduce congestion. McMahon was selected in 2010 by the City to perform traffic signal retiming and optimization on multiple signalized arterials (up to 21 arterials total encompassing over 600 intersections). Our tasks under this assignment included extensive traffic volume data collection, including automatic traffic recorders and manual turning movement counts, pedestrian traffic counts, before and after travel time and delay studies utilizing new technologies, such as Bluetooth readers. McMahon also analyzed and evaluated existing corridor operations including multi-modal considerations, detailed capacity analysis of existing conditions, and final capacity analysis to optimize corridor operations, which in-turn prepared work orders for city personnel to implement the proposed traffic signal timings updates. We also assisted the City with the timing implementation.