A method to define public transit opportunity space

A public transit performance measure quantifying the ease of reaching a destination from a given location is important for describing the efficiency and convenience of public transit. In this paper, a new method for quantifying public transit performance, the Transit Opportunity Index (TOI), is presented. This measure accounts for both transit accessibility (the level of access to the transit system) and transit connectivity (the system’s provision of services between origins and destinations) by combining measures of spatial coverage, temporal coverage, and trip coverage. Spatial and temporal coverage measures are calculated using an origin–destination (O–D) representation of the transit network and then combined to create a transit accessibility score for each O–D pair. Transit accessibility is weighted by a binary connectivity parameter and a connectivity decay factor. The connectivity decay factor is derived from a travel time-based logistic function to reflect the decreasing connectivity with increasing travel time. The binary connectivity parameter and the connectivity decay factor are used to account for trip coverage, or transit connectivity. The Transit Opportunity Index (TOI) is then applied to the bus network of the city of New Haven, Connecticut. The results of this case study suggest that the TOI is a more complete and practical measure of public transit service performance than previously established measures. This method also has the potential to identify transfer zones for public transit trips between O–D pairs without direct connections. However, the TOI is most powerful when used in conjunction with a public transit demand measure to identify underserved areas.