INVESTIGATING THE PROSPECT OF INTRODUCING TIDAL FLOW OPERATION BETWEEN GLOBE-INTERCHANGE AND KASARANI SECTION OF NAIROBI-THIKA ROAD

Most cities in Africa characteristically experience peak time traffic due to the commuter lifestyles of urban area residents. Therefore, in the morning roads leading to the central business district of most towns experience congestion while those leading out tend to have free flows. Traditional methods of solving this congestion problem such as additional roadway capacity have proved to be ineffective and overly expensive. Therefore, Solution of this kind of traffic congestion problem calls for other transport intelligent methods.
Incorporation of tidal flow designs on roadways presents a potential method of dealing with peak-time traffic congestion. A tidal flow operation is a traffic management process whereby the carriageway width is shared between two directions of travel in near proportions to the flow in each direction with the lanes of the roadway width being referred to as Dynamic Tidal Flow Lanes (DTF-lanes). This implies that the direction of traffic lanes is designed to be reversible according to the traffic demands. A well-designed tidal flow operation will ensure a very cost effective method of traffic management in the areas that experience high directional peak flows.
This study was in effect carried out to examine the viability of introducing tidal flow operations in Nairobi with Nairobi-Thika highway being used as the case study. The section between Kasarani to Globe Roundabout of the highway was chosen for the study. The section was chosen because it notoriously experiences directional peak congestion. With large traffic volumes in one direction during peak times, the highway width in the opposite direction remains under-used while the peak direction experiences congestion and delays. This in turn means that the highway is not effectively utilized at the peak times. A lot of useful space is left under-utilized; an uneconomic way of resource utilization.
In the study different road sections were checked for the conditions necessary to implement a tidal flow such as periodicity, distinctness and predictability of the flow and capacity for traffic dissipation at the ends of tidal lanes. This was by analysis of typical daily (12hrs) variation of traffic characteristics e.g. volumes and daily dynamism of the level of service. On determination of sufficiency, a tidal flow was designed by traffic micro-simulation approach using PTV VISSIM traffic simulation software. Computer simulation proved to be a vital adjunct to traditional traffic engineering analysis methods in fully understanding the dynamics of traffic movement and control operations. The simulation tools were critical in the development and evaluation of new ideas, algorithms, and traffic control systems.
The model’s capability of evaluating detailed traffic performance at interchanges/intersections, along highway/arterials and the whole transportation network provided a detailed objective operational analysis of traffic control features. The models also afforded the opportunity to evaluate traffic control and design strategies without committing expensive, time-consuming resources necessary to implement the alternative strategies in the field.
The study provides conclusion and recommendations on the adoption of tidal flows for traffic management and appropriate design approach that ensures efficiency in traffic flow and safety for all users including non-motorized traffic (NMT).