McMahon provided transportation engineering and conceptual design services on the design team for the Casey Arborway project. 

The structurally deficient Casey Overpass, which is part of the Arborway (Route 203) needed to be replaced. In the planning stage, McMahon undertook a vast multimodal data collection effort, determined existing and projected traffic volumes, analyzed the traffic operations, prepared VISSIM traffic simulations, developed conceptual designs for both at-grade and bridge replacement alternatives, and participated in extensive public outreach. The study area is located in the vicinity of the Forest Hills MBTA Station in the Jamaica Plain section of Boston, and the concepts developed were multimodal in nature. McMahon coordinated with the City of Boston and the Central Transportation Planning Staff (CTPS) to develop the future volume projections for the transportation modes. The evaluations of the alternatives considered local and regional elements; mobility and livability issues including operations; enhancements for the connectivity between business, residential, and recreational uses; and the restoration of the Emerald Necklace connection through this corridor. 

McMahon developed an at-grade solution that allowed for the removal of the bridge while providing for future vehicle operations and significant pedestrian, bicycle and landscape enhancements. McMahon’s final design services included traffic analysis, assistance and quality review of the traffic signal design for 12 locations, agency coordination, public outreach, and assistance with pavement markings, signage and construction staging, including development of temporary traffic signal timing plans for each construction stage. The traffic signal design includes innovative features such as lead pedestrian intervals, bike crosswalks and signals, and an exclusive bus lane and signal phase. 

In addition to design services, McMahon also provided construction services, particularly as it related to the signal timings and traffic management. The project was completed in 2019.