Evaluating service mitigation proposals for the MBTA Green Line extension construction delay using simplified planning methods

Abstract

This thesis reviews a select group of transit environmental mitigation proposals through the application of ridership estimation methodologies. In recent years, rider demands and environmental concerns have led many transit agencies to explore options for increasing service even within constrained budgets. Anticipated state and metropolitan area climate change mitigation strategies are likely to result in the need for further transportation system changes in many cities. In response to environmental concerns raised during the construction of the Central Artery/Tunnel, Massachusetts committed to extending the Green Line light rail from its Cambridge terminal at Lechmere into Somerville and Medford. The Massachusetts State Implementation Plan requires that the Green Line be extended in two branches by the end of 2014. Massachusetts has delayed construction on the extension, and it must therefore undertake mitigation for the delay. Facing both financial constraints and pressure to increase service, transit agencies such as the MBTA need new ways to improve transportation systems with limited financial input and means by which to evaluate the impact of proposals. Several mitigation proposals focusing on transit services in the Lechmere Station area are presented in this thesis. Increasing service on the Green Line to Lechmere is found to be a good first step towards improving service in Somerville. Proposals for increasing bus feeder service to and from Lechmere and the surrounding areas include both increasing service on existing routes and introducing new routes. Partnerships with existing private providers could also help decrease the costs to the MBTA of introducing a new route. In order to analyze the mitigation proposals, several methodologies are explored including area wide transportation planning models, direct demand (regression) models and comparison equations. A rail elasticity of demand with respect to service is calculated based on a prior MBTA system experience, while elasticities from literature are used for buses. In addition, a direct demand model is estimated for the MBTA bus network, and the results are compared to elasticity analysis. Regional planning models are found to be important for predicting system-wide responses but often are too detailed and expensive to use to evaluate every proposal. Instead, direct demand models can help with initial rankings of proposals, and service elasticities can help further examine expected ridership changes due to service improvements.