Importance of objectives in urban transit-network design

Stop spacing and line spacing are key design variables in urban transit-network design. They determine both the travel time and the operational costs. It is therefore essential to know what the main relationships are for these design variables. The question is, What are the optimal values for stop spacing and for line spacing in urban transit networks, given traveler preferences and supply-budget constraints? Possible objectives are discussed and analyzed using analytical models. The results of these analytical models for two typical city types are analyzed by comparing performance characteristics (i.e., travel time, operator costs, and patronage). Modeling outcomes are compared with actual data for urban transit networks in Europe. A supplemental analysis is made of the impact of considering different traveler groups. It was found that although many objectives may be formulated, only a few objectives are suitable for transit-network design. Currently applied stop spacings prove to be too short. Focusing the design to specific traveler groups might lead to a variation of stop spacing and line spacing ranging from -12 percent to +13 percent at most. Recommendations for urban transit-network design and for further research are given.