The Boston Region Metropolitan Planning Organization (MPO) selected Route 138 in the Town of Canton as the subject of a corridor study in federal fiscal year 2017. The Route 138 Priority Corridor Study focuses on one of the locations identified in a regional needs assessment—conducted as part of the MPO’s Long-Range Transportation Plan, Charting Progress to 2040. This report presents details of the analyses of existing conditions, assesses safety and operational problems in the corridor, discusses options for roadway improvements, and makes recommendations for implementing improvements. If the report’s recommendations are implemented, they should result in Complete Streets benefits, such as enhanced pedestrian and bicyclist accommodations, increased traffic safety, more efficient traffic operations, reduced congestion, and promotion of multimodal transportation. The report contains technical appendices, which cite the methods used and data applied in the study, and include detailed reports about intersection capacity analyses.