Multimodal Transport in Nairobi, Kenya: Insights and Recommendations with a Macroscopic Evidence-Based Model

The limited street network in Nairobi, Kenya, is crowded with cars and matatus (informal transit). This paper studies the existing traffic performance using traffic simulation. Despite the poorly connected, asymmetric street network, there is a consistent relationship between aggregated traffic variables for the city center, namely the number of vehicles circulating in the network and the rate at which trips reach their destinations. This relation is called a macroscopic fundamental diagram (MFD), and shows how the capacity of Nairobi's streets compares to the capacity of streets in other cities. The MFD also shows how traffic delays will increase with continued growth in demand. This method of looking at traffic performance is also used to identify policies which will improve traffic conditions in Nairobi. These policies include metering the rate that vehicles enter the city, spreading peak demand, improving intersection operations, dedicating lanes to buses and matatus, and strategically adding redundant links to the network. If nothing is done, traffic conditions in Nairobi will get worse, but by monitoring traffic and adopting some cost-effective policies, the capacity of the network to serve trips can be substantially improved.