Simulation Models Assess Cost Differences Between Expanding Traditional Transit and Implementing App-Based Shared Mobility.
Seattle, Washington, United States
Supplementing Fixed-Route Transit With Dynamic Shared Mobility Services: A Marginal Cost Comparison Approach
Summary Information
In recent years, shared mobility has gained popularity as smartphones and location-based service apps have become increasingly widespread. As a result, many public transportation agencies started to study the feasibility of incorporating shared mobility into their transit services. This study developed a framework based on the economic concept of marginal cost, aimed to determine the cost difference between implementing app-based shared mobility options and expanding “traditional transit”. The study created a simulation model and applied it to evaluate an existing pilot project named Via to Transit, a transit supplementing on-demand mobility service of King County Metro (KCM) in the Seattle region, by using its ridership data collected in 2019. Via to Transit pilot employed on-demand, accessible shared mobility services as a first-mile/last-mile solution for connecting people located within specified service areas to one of five Link light rail stations of KCM.
METHODOLOGY
The study consisted of two parts. First, it developed a theoretical framework to analyze the costs of various transportation options, based on three principles: (i) using marginal cost rather than average cost for decision-making; (ii) considering both service provider and user costs; and (iii) including all components of user travel time, such as in-vehicle, access, waiting, and egress times. Next, the study developed a simulation model of the study area to depict scenarios where Via to Transit did not exist, and all current Via to Transit riders used alternative modes instead. Fixed-route transit and driving alone to/from park-and-ride facilities were the two modes considered. An open-source microscopic simulation software tool was employed to simulate Via traveler’s trips using alternative modes for the analyses. Total generalized cost for alternative modes of travelers was calculated by combining the time cost from the simulation model (access, waiting, in-vehicle travel, and egress times) and the monetary cost.
FINDINGS
- On average, Via to Transit had a travel time of 19.4 minutes. If trips were diverted to the two bus routes with their existing service frequency, the average travel time would increase to 27.3 minutes (a 30 percent increase). The longest trip duration increased by 23 percent, from 43.0 minutes to 53.1 minutes.
- If the frequency reached a high level with a 5-min headway, bus trips became nearly equivalent in performance to Via (19.4 minutes versus 19.7 minutes), highlighting the time-saving benefits of Via to Transit's on-demand and flexible nature compared to fixed-route buses.
- Via to Transit proved to be a better choice than relying solely on transit for longer trips. However, for trips less than 1.5 miles, Via to Transit did not offer an advantage over buses.
- Although the shortest travel times were still achieved by driving alone, primarily because it does not require waiting and detouring like Via does.
- The economic analysis showed that when travelers’ total generalized costs were incorporated, the Via to Transit pilot is more economically cost-effective ($5,278) than running fixed-route transit at the current frequency ($6,729).
