Date of Award

7-13-2026

Thesis Type

PhD

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Divisions

Faculty of Engineering

Department

Department of Civil Engineering

Institution

Universiti Malaya

Abstract

Traffic safety at roundabouts is an important concern in Malaysia, where motorcycles form a major component of mixed traffic. Motorcyclists are particularly vulnerable because their smaller vehicle size allows greater manoeuvring flexibility, which may contribute to risky behaviours such as improper lane selection, close-distance stopping, lane splitting, and failure to signal. This study examines the relationship between roundabout geometry and risky motorcyclist behaviour under mixed-traffic conditions in Kuching, Sarawak. Video data were collected using drone and roadside cameras at four selected roundabouts, comprising multi-lane roundabouts and one single-lane baseline comparison site. A total of 15,937 motorcyclist observations were coded into six risky behaviour categories: EN1, EN2, EN3, C1, EX1, and EX2, representing entry, circulation, and exit-stage behaviours. Five geometric variables were examined, namely entry width, entry radius, exit width, exit radius, and number of circulatory lanes. Multiple regression analysis was used to quantify the association between geometry and risky behaviour event rates per 100 motorcyclists, while CHAID analysis was applied to identify threshold-based behavioural patterns. The regression results showed that entry width was strongly associated with improper lane detection and close-distance stopping behaviours, while entry radius was more closely associated with failure to slow down before entering. For exit behaviours, exit radius was strongly associated with improper exit path selection and failure to signal before exiting. Circulation-related lane splitting was more evident at roundabouts with more circulatory lanes, although this behaviour should be interpreted together with traffic operating conditions. CHAID analysis further showed that entry radius was the primary splitting variable, indicating that risky behaviours varied across different geometric threshold conditions. Overall, the findings suggest that roundabout geometry is associated with distinct risky motorcyclist behaviours under peak-hour mixed-traffic conditions. The study contributes methodologically by combining regression and CHAID analysis to examine both overall geometry–behaviour relationships and conditional threshold patterns. Practically, the findings provide preliminary design-oriented insights to support more motorcycle-sensitive roundabout design considerations in Malaysia.

Initial

khm

Additional Information

Thesis (PhD) - Faculty of Engineering, Universiti Malaya, 2026.

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