Explaining transit ridership: What has the evidence shown?

What explains transit ridership? The answer to this simple question is both obvious and complex. Public transit systems carry large shares of person travel in older, larger metropolitan areas around the globe, but in most places, old and new, large and small, transit is losing market share to private vehicles. A host of factors no doubt influence transit ridership, including fares, routing, service frequency, stop/station accessibility, safety, private vehicle ownership levels, population density, land use, parking availability, and cost. But the relative importance of these factors and the ways they influence one another is less well understood. At the same time, the relationships between these factors and transit ridership are central to public policy debates about transportation system investments and the pricing and deployment of transit services. The research explaining transit ridership is surprisingly uneven, spanning a variety of methodological approaches, data sources, and variables that produce, perhaps not surprisingly, somewhat ambiguous, contradictory, and inconsistent results. Yet the factors affecting transit ridership are not simply matters of academic interest. Public investment in transit is waxing in response to the many problems of auto dependence, worsening traffic congestion, rising fuel prices, vehicle emissions, and so on. What can be done to increase patronage and better leverage these investments? To address this question, this paper reviews research on transit use, critiques the sometimes significant weaknesses in much of the previous work on this topic, draws conclusions from the more rigorous studies about which factors most influence transit use, and presents recommendations for future research.