Assessing Functions of Bypass Roads in Cities and Towns: a Case Study of Eastern Bypass in the City of Nairobi

Abstract

Functions of bypasses and their impacts have been assessed in various studies worldwide. These roads are key in addressing traffic congestion, environmental pollution, road accidents and economic growth in cities and towns. Nairobi’s Eastern Bypass is one such road constructed mainly as an alternative route for both local and traffic on transit in the City of Nairobi. However, after opening the bypass to traffic, it attracted unexpectedly high volumes of traffic and failed to function as a bypass in a short period. In this study, functions of Eastern Bypass in the City of Nairobi were assessed specifically to establish trip composition and traffic mix, traffic flow characteristics, current and future traffic and congestion levels based on traffic volume counts, origin and destination, and travel time and delays data. The study also compared various features along Eastern Bypass and bypass standards. In summary, the study established that 43% of vehicles that operated along Eastern Bypass consisted of of cars and taxis, large cars, 4wheel drives, jeeps, pickups and vans; 35% were goods vehicles and 9% were public service vehicles among others. Again, approximately 12% of trips along Eastern Bypass consisted of local trips and 22% through trips while the rest of trips were either internal – external or external – internal trips. Still, the study established that over 39,295 passenger car units (PCUs) passed along Eastern Bypass daily or 1,638 PCUs per hour. Projections of this traffic indicated that over 123,325 PCUs will pass along Eastern Bypass per day or 5,139 PCUs per hour by 2029. This volume was comparatively higher than the projections in the feasibility study carried out for the bypass in 2007. Again, most vehicles along Eastern Bypass had their origins and destinations in counties and regions in Eastern, Central and North Eastern Kenya. This was attributed to the location of Eastern Bypass relative to these regions. On congestion, the study found that the dualled section of Eastern Bypass and locations with grade separated junctions experienced speeds between 70km/hr and 80 km/hr corresponding to levels of service ranging between B and A. However, sections of Eastern Bypass with single carriageways operated at levels of service between C and F. Finally, the study established that few features along Eastern Bypass meet bypass standards.