Traffic congestion significantly contributes to climate change due to the emissions of Greenhouse Gases (GHGs) such as Carbon Dioxide (CO2), Nitrous Oxide (N2O) and Ozone (O3). Rapid urbanization and poor planning coupled with increased motorization and fragmented public transport system in cities such as Nairobi has led to increased vehicular emissions along the various roads and within the Central Business District (CBD). To reduce GHG emissions in the urban transport sector, institutional coordination and relevant policy tools must be considered. The aim of this study was to estimate CO2 emissions from different vehicle categories during congestion, using Uhuru Highway as a case study. The relationship between traffic congestion and CO2 emissions was analysed using qualitative and quantitative methods, through a bottom-up approach. Both primary and secondary data were used in this study. Questionnaires were administered to get individual vehicle characteristics and opinions on the best actions for reduction of CO2 emissions along Uhuru Highway in Nairobi. The Average Annual Daily Traffic (AADT) for different vehicle categories from 2014 to 2019 formed the basis for estimation of CO2 emissions. Results showed that private cars predominate over other vehicle types, contributing 73% of the total CO2 emissions in Nairobi Central Business District (CBD). Private cars are the highest contributors of CO2 emissions with a total of 25.3 million of Carbon dioxide equivalent (gCO2e), between 2014 and 2019. In comparison, Public Service Vehicles, commonly referred to as Matatus emitted 6.89 million gCO2e, Light Commercial Vehicles (1.82 million gCO2e), Heavy Goods Vehicles (251,683 gCO2e) and motorcycles (181,054 gCO2e). To minimize CO2 emissions, the study recommended enforcement of strong mobility policies to control the high motorization rate. One of these policies is the prioritization of the development of mass public transport system to achieve the potential health, economic and environmental gains within the CBD.

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