Investigating the impact of vehicle speed and traffic volume on headway along two-lane bituminous highways in Uganda.

Abstract

Rear end accidents pose a significant challenge on two-lane bituminous highways in Uganda, necessitating the thorough investigation of their causes and potential mitigation strategies. This research aims at understanding the relationship between vehicle speed, traffic volume and headway along a typical two-lane highway. By analysing how these factors influence the headway between two successive vehicles, the study aims to provide insights on how these factors impact the occurrence of rear end accidents / collisions. The research employs a quantitative approach using data collected through field observations and measurements along Kampala - Jinja highway which is a two-lane highway with heterogenous traffic conditions. The data was gathered from a selected road segment with a clear sight without intersections that would cause diversion or interruption of speed in the traffic and free from commercial activities. The collected data was analysed using Microsoft Excel from which graphs were plotted to assist in the development of relationships between traffic volume and headway, vehicle speed and headway. From the findings, it was observed that an increase in vehicle speed leads to an increase in headway and that for every 10 km/h increase in the vehicle speed there is a 0.79 second or 20.8 metre increase in the headway between successive vehicles on Kampala - Jinja highway. Conversely, the headway between succussive vehicles on the highway reduces with increase in traffic volume and for every additional 100 vehicles added to the vehicle streams every hour on the highway, there is a 0.5 second or 4.68 meters spacing or time headway reduction between successive vehicles, this thereby increasing the likelihood of occurrence of rear end collisions. These findings shed light on the dynamics of headway variations on two-lane highways and their implication on rear-end accidents. To minimise rear end collisions on Ugandan highways, average vehicle speeds along two-lane highways should not fall below a safe following speed of 27 km/h as obtained in this research. Also, dualizing the major highways through lane addition to ensure that the traffic volumes do not exceed 855 vph per lane which is the critical traffic volume obtained from this study would enhance safety and minimize the occurrence of rear end accidents on two-lane highways in Uganda.