Handling Non-Motorized Trips in Macroscopic Travel Demand Models : Calculating Intrazonal Impedances and Identifying an Appropriate Level of Spatial Resolution

Non-motorized trips are generally short trips, and in macroscopic models, many of them end up in the same transport analysis zones from which they originate. Since the spatial aggregation nature of these models makes it difficult to model intrazonal trips, the treatment of non-motorized trips in such models is limited. Non-motorized trips can however not be neglected in urban transport analyses considering the high share of walking and cycling in urban areas, and their importance for sustainable mobility. Recognizing the mitigation of the intrazonal problem as key to improving non-motorized trip modeling in macroscopic models, the research seeks to enhance the macroscopic modeling of non-motorized trips by finding a suitable method for calculating intrazonal impedances, and identifying an appropriate level of spatial resolution for analysis zones. To find a suitable method for calculating intrazonal impedances, the study compares both calculated intrazonal impedances and modeled intrazonal trips. The study considers existing methods for calculating intrazonal impedances and a new method that calculates intrazonal impedance by finding the average impedance between node pairs within a zone. The results show that whereas the proposed method provides better estimates of intrazonal impedances, better intrazonal impedance estimates do not guarantee better intrazonal trip estimates. Consequently, non-motorized trips cannot be adequately handled in macroscopic models by improving the calculation of intrazonal impedances. Efforts aimed at improving the calculation of intrazonal impedances should therefore be geared towards reducing the need to deal with intrazonal trips. In identifying an appropriate level of spatial resolution, the study seeks to minimize a cost function with respect to the number of zones and the deviations in traffic assignment results. The objective is to keep the number of zones to the minimum possible while ensuring low deviations in assignment results. Using network length per zone to define spatial resolution, the study applies the gradual rasterization process with the quadtree concept to create 24 different raster cell systems for different levels of spatial resolution. The study identifies 1,000 m network length per raster cell as an appropriate level of spatial resolution for the study area and indicates the possibility of adjusting input variables to define context-specific appropriate levels of spatial resolution. The results show that there is a limit beyond which the benefits derived by further increases in spatial resolution is not worth the costs associated with the extremely high increase in the resultant number of zones. The application of the research findings in the travel demand model of Dachau confirms that mitigating the intrazonal problem improves the modeling of non-motorized trips. The research outcome should facilitate the integration of bicycle and pedestrian travel in the models of planning agencies to enable impact assessment of actions taken to encourage non-motorized travel. This will ensure the successful development and implementation of sustainable mobility concepts.