Gradual rasterization: redefining spatial resolution in transport modelling

It is a challenge to find the appropriate level of spatial resolution in transport modelling. While the zone system has substantial influence on model results, the resolution and design of zones is rarely analyzed systematically, and even less commonly adjusted to a specific modelling need. In this paper we present a new methodology to automatically create a new zone system based on the quadtree algorithm specific to transport modelling. Gradual raster cells are generated, where smaller raster cells tend to be used in urban areas and larger raster cells dominate in low-density, rural areas. As changing the zonal resolution affects the number of intrazonal and interzonal trips, an algorithm has been developed that adjusts intrazonal trips in line with the network resolution. Trip tables of a travel demand model for the state of Georgia, USA were disaggregated using this new zone system of gradual raster cells. The traffic assignment results validate significantly better than when using the original zone system.