Are Park-and-Rides Saving the Environment or Just Saving Parking Costs?

Abstract

Rising greenhouse gas (GHG) emissions have put public transit at the forefront of the push for more sustainable transportation. To improve transit accessibility and attract riders, agencies often build park-and-ride facilities on the periphery of cities. Through the provision of convenient parking facilities, agencies attempt to encourage drivers to shift modes and leave behind their cars to complete their journey by transit. Although park-and-rides are intended to increase transit ridership, such facilities may carry paradoxical environmental consequences. At issue is the degree to which such a multimodal car-to-transit trip actually offsets GHG emissions. The study reported in this paper examined single-occupancy vehicle (SOV) park-and-ride users in the Denver, Colorado, metropolitan area and evaluated the magnitude of GHG emissions saved from transit ridership. Through a comparison of a multimodal trip against a theoretical SOV drive-only trip, the effects from GHG emissions were weighed. In addition, the environmental opportunity cost of park-and-ride stations was assessed through the repetition of the analysis under the assumption that all park-and-ride transit users that originated from within a 2-mi radius would shift modes to walk or bike rather than drive an automobile to the station. The results suggested that park-and-rides located at inner-corridor stations were far less effective in reducing GHG emissions than were end-of-line stations. This ineffectiveness appeared to be exacerbated by a parking fee structure common to both the inner-corridor and end-of-line stations. If the goal is environmental sustainability, the location of a park-and-ride facility at almost every station should be reevaluated in favor of a strategy that focuses on how and where park-and-rides can be most effective. The results of this study suggested that inner-corridor stations, particularly those closest to a downtown area, induced unnecessary driving trips and provided an incentive for longer SOV transit-access car trips.