What's eating public transit in the United States? Reasons for declining transit ridership in the 2010s

Despite ever-increasing public and financial support for public transportation in recent decades, transit ridership has dropped substantially in the 2010s across the United States. While many theories that explain the reasons behind the decline in ridership have been proposed, no consensus on the primary causes has been reached. By employing gradient boosting decision tree and counterfactual simulations, we examine the complex relationships between transit ridership and key internal and external factors from 2002 to 2017 in 85 of the largest urbanized areas in the US. Among several contributing factors, the declining cost of driving, measured by the decreasing share of carless households combined with lower gasoline prices, was the salient, most influential factor behind the recent decline. Neighborhood change in high-density neighborhoods also led to a moderate net loss in ridership. The only factor that has been mitigating further decline was an increase in transit services. Had this increase not occurred, loss of ridership would have been more than double the actual loss during the study period.