Analysis of the causal effects of exclusive bus lanes on performance indicators of public transport corridors

Exclusive bus lanes are frequently recommended in the literature to enhance transit efficiency. However, the improvements reported by transport agencies following bus-only lane interventions often lack rigorous evaluation using causal inference methods. This gap raises concerns about potential biases and the omission of relevant covariates that could influence the outcomes. Addressing these issues is crucial, particularly in understanding both the direct and indirect effects of exclusive bus lanes on operational indicators like speed and reliability, given the cyclic relationship between transit level of service and ridership. This paper therefore investigates the causal relationships between the determinants of public transport operations and examines how these factors are altered by exclusive bus lanes. We aim to estimate the direct and indirect causal effects of such interventions using a comprehensive approach that begins with the creation of a mental map outlining the key determinants affecting public transport demand and performance. This is followed by the development of a causal diagram to estimate the impact of bus lane interventions. To demonstrate the practical application of this approach, we conducted a case study assessing exclusive bus lane interventions in the transit corridors of Fortaleza, Brazil, using observational data from the system’s operation. Our findings contribute methodologically and practically by offering transport planners and practitioners a framework for assessing bus lanes effects on bus speed and reliability, as well as understanding how these lanes can indirectly influence these outcomes through increased ridership, stressing the importance of rigorous policy evaluation in public transport planning.