Is the relationship between bus and light rail transit a competition substitution or a congestion substitution? An empirical study in Seattle

Public transit in Seattle has achieved success, with increases in transit ridership during these years, while most U.S. cities face a decline in transit ridership. It is worth learning the experience from Seattle's transit success, but the causes remain unclear. This study hypothetically attributes this success to a good cooperation between public transit modes and uses quantile regressions to prove this hypothesis. Based on a bus stop ridership of 2988 in 2017, results indicate that the differences between bus stops within light rail transit catchments and outside catchments are significant and prove the relationship as the substitution of light rail transit for bus services. We further identify the situations when substitution happens and find it only happens in areas with high bus ridership, as congestion substitution. Besides, bus rapid ride lines and land-use factors are significantly associated with bus ridership. Conclusively, our study proves that the good cooperation between light-rail transit and bus service and transferring facilities could be a success story in the Seattle public transit service. This study can contribute to policymakers allocating public transit budgets wisely and suggest that a good cooperation between public transit modes can be a potent way to promote public transit ridership.