Circular buffers and isodistances as methods to designate catchment areas for public transport: a comparative analysis

An important aspect of an efficient transport system in urban areas is to provide passengers with a high level of access to public transport stops. In areas with dense and diverse development, locating such facilities in the transport network is a significant challenge and a complex decision-making problem. Therefore, it is necessary to support it with appropriate analyses before making the final decision. Many approaches in this field require spatial determination of the range of impact in the form of a catchment area, which can be constructed in various ways. Therefore, the study aimed to compare two methods for designating catchment areas of public transport stops in urban locations, i.e., circular buffers and isodistances, to support more informed decisions. The novelty of the approach was to enable a comparison of both approaches at the level of individual stops and the entire network, and the introduction of a way to designate the optimal buffer radius that best approximates the isodistance-based area. A new measure based on the weighted average percentage of area coverage is introduced. Such analysis allows us to use both approaches interchangeably. The analysis was conducted for the public transport stops in a large metropolitan area in southern Poland, GZM Metropolis (Górnośląsko-Zagłębiowska Metropolia), which differed both in terms of their location with respect to the city center and in terms of the structure of the surrounding road and street network adapted to pedestrians. The results of the analysis suggest that the percentage of buffer and isodistance coverage with the same radius sizes and values may range from about 34% to 61%. Based on the performed analysis, the best results of the substitution of the isodistance model with the circular buffer model are obtained if the buffers are 100-200 m smaller than the isodistances. In future work, it is also worth examining the dependence of the values of the analyzed measures for a single public transport stop, as well as the average values for the entire set of stops, on the parameters of the road and street network within the buffer or isodistance.