Investigating the effect of road geometric parameters on the manoeuvrability performance of transit buses at junctions within Kampala

Abstract

Road geometric parameters, which are the dimensions and design features that define a road’s physical layout, significantly influence the manoeuvrability performance of transit buses, especially at junctions. Just like many developing cities worldwide, Kampala through the Kamapala Capital City Authority (KCCA) intends to introduce and successfully implement a public Bus Rapid Transit (BRT) system in order to curb issues such as congestion. However, there has been little research on whether the existing road infrastructure in Kampala can support such a system. Therefore, the main aim of this research was to investigate the effect of road geometric parameters on the manoeuvrability performance of transit buses at junctions within Kampala. By ensuring that these parameters exceed adequacy, it is possible to mitigate curb and lane infringements, reduce the complexities of making manoeuvres, and consequently minimize the risk of accidents, thereby enhancing manoeuvrability performance and promoting the use of transit buses as a preferred means of public transportation. This study collected data through field measurements using a Global Navigation Satellite System (GNSS) receiver at thirteen diverse junctions. The data was imported into AutoCAD software, and the manoeuvrability performance metrics were evaluated using swept path analyses, facilitated by the Autodesk Vehicle Tracking software plugin. The simulations assessed the movements of two types of transit buses—Bus A, a standard bus, and Bus B, an articulated bus, both sourced from the Autodesk Vehicle Tracking software vehicle library. The manoeuvrability performance outcomes were quantified using a formula that calculates the proportion of routes successfully navigated by the buses relative to the total available routes at each junction type, as a measure of junction performance. The parameters analysed included lane width, number of lanes, road width, curb turning radius, intersection / circulation area, main carriageway width, and extreme flare width. The study found that the manoeuvrability performance of the transit buses improved with increases in each of these parameters. Notably, Buses A and B achieved baseline manoeuvrability performances of 54.00 % and 41.00 %, respectively, based on the minimum recommended values from the Ministry of Works & Transport. A sensitivity analysis with a ± 10 % variation in parameters identified lane width as the most sensitive, followed in descending order of sensitivity by curb turning radius, main carriageway width, road width, and extreme flare width.