Network optimization to improve accessibility in Bangkok

18 Oct 2022
The Sasin Research Seminar series continued with a presentation looking at accessibility in Bangkok by Assistant Professor Stefano Starita. The research aims to improve pedestrian access to critical services, such as schools and hospitals, by increasing the number of walkable paths in Bangkok. The talk began with Assistant Professor Starita giving an example of a one-kilometer walk in a Bangkok district. Some sections were accessible for all, including the disabled, but others were missing pavements, required overhead crossings, or were unpassable for all, often ending in a dead end. As Bangkok’s population gets older, this poses a growing problem. Three types of pathways were identified. Those that were accessible to all were labelled white. Those that were just for walkers and not the disabled were yellow. And blocked paths were marked red. The Assistant Professor showed the districts he selected for the research. Covering the whole of Bangkok would be impossible, so he picked a typical region of the city with highly clustered neighborhoods, a network of sois, and major roads. He then showed all the routes with the white, yellow, and red added. The research wants to show how infrastructure investment could turn red and yellow links into white ones and assumes there is a budget. But where should the money go, and what needs improvement? A new map was shown with groups of people as orange dots and places they might want to go, such as schools and hospitals, marked blue. These locations should be accessible to those without cars. This information was combined with the previous map. The idea is to make sure suitable investments are made. For example, where can blue dots be added or red lines changed? Next was how the data was collected. OpenStreetMap was used, and the assumption was made that residential areas were accessible for all and could not be improved. The initial research found 60kms of roads proved to be walkable and wheelchair friendly, with 32km accessible to just walkers (orange) and 28km inaccessible to all (red). The problems with budget allocation were discussed. Next was a look at network optimization and using algorithms and mathematical optimization to design, manage and improve a network’s performance. The best way to use mathematics to calculate models was discussed, including factors such as the cheapest, shortest, and quickest path, and maximum flow. For network design, the research looked at which assets, such as nodes and links, would create the best-performing network. Regarding network design and accessibility, the study asked what road segments should be improved (or built) and where more facilities nodes should be placed. Different views of the maps and nodes were examined, showing the complexity of the data. The existing literature was then discussed, including studies on network design, accessibility, and walkability. The Shortest Path Problem was examined. This assumes that traversing a link comes at a cost, such as distance or time. The idea is to find the lowest cost path between nodes. Assistant Professor Starita numbered the links and showed some of the calculations used, mathematics, and variables. He discussed how the paths could be described and revealed the complex mathematical equations that could explain them. He also looked at how the equations could be developed and how new nodes could be added. He then discussed the next steps, such as adapting the shortest path problem to incorporate accessibility and running analysis under different scenarios. This was followed by current limitations and issues to address, including outdated data, problems with complexity, and the lack of incorporation of environmental issues. The talk concluded with the expected outcome. This would be a systematic tool that could tell, for a given budget, where road enhancement or additional facilities should be built to benefit the community. The presentation was followed by a Q&A session that looked at how this was computed, which areas would be covered, and discussed similar studies.  
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