Discussion Paper No. 128 of 2012 on Evaluating the Impact of Road Traffic Congestion Mitigation Measures in Nairobi Metropolitan Region

Abstract

Traffic congestion is a major problem in many cities around the world, including the Nairobi Metropolitan Region (NMR). Given the high economic, social and environmental costs incurred on account of road traffic congestion, the Government of Kenya as well as other actors have planned and implemented various strategies in an effort to mitigate these negative effects. This study evaluate the effectiveness of road traffic congestion mitigation measures in the NMR, aiming to establish strategic options that could be used to mitigate the problem of road traffic congestion. The methodology used in this research was based on the Four Step Model (FSM) of travel demand forecasting. A FSM of travel demand in NMR was built using Geographical Information Systems (GIS) and this was followed by simulation of the effects of implementing different traffic congestion mitigation measures. Results from data analysis reveal that the problem of traffic congestion will be significantly worse by the year 2030, if no measures are taken to address it. Traffic congestion in NMR is influenced by both demand and supply side factors. It also emerges that majority of traffic flows were concentrated in the central area of Nairobi city. The results of the simulations reveal that increasing the capacity of roads has the greatest effect on reducing congestion. Implementation of the modal shift strategies has the second-best effect on reducing congestion. The third best mitigation strategy is building the bypass roads and missing links, while implementation of multi-centric development of the NMR is fourth. A combination of all mitigation measures yield a significant reduction in road traffic congestion, representing a 70 per cent decrease. It is observed that traffic flows on the major roads in Nairobi city follow a temporal pattern of high flows that coincide with hours in which most work trips and home trips are executed.