Effects of Rainfall on Driver Behaviour and Gap Acceptance at Multilane Roundabouts

Stephen Ibijola, Johnnie Ben-Edigbe*
Department of Civil Engineering, University of KwaZulu-Natal, Durban, South Africa

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Creative Commons License
© 2018 Ibijola and Ben-Edigbe.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Correspondence: Address correspondence to this author at the Department of Civil Engineering, University of KwaZulu-Natal, Durban, South Africa; Tel: +27(031)2602005; E-mail:



This paper filled an important gap in the behaviour of driver and gap acceptance model at multilane roundabouts by investigating their traffic performances during rainfall.


The study carried out an investigation into the impact of rainfall on driver’s behavioural changes and gap acceptance characteristics. Follow-up time headway and gap time were used as proxies.


Traffic volume, speed, vehicle type and headway data were collected at selected multilane roundabouts in Durban, South Africa. All surveyed roundabouts are within rain gauge catchment area of about 1km. Rainfall intensity was divided into three groups (light, moderate, and heavy). Dry weather data were used as control parameters.

Data Analysis:

Stepwise data analytical technique was used for ease of explanation and clarity. All model equations were tested for statistical fitness and deemed satisfactory for further analysis.


Based on the synthesis of evidence obtained from driver’s behavioural changes and gap acceptance characteristics at multilane roundabouts, the paper concluded that it is correct to suggest that rainfall would have a profound effect on follow-up time headway and critical gap acceptance. However, the effect diminishes gradually as volume to capacity ratio approaches peak traffic operation. Once the threshold value of 0.85 is reached the diminishing effect of rainfall as the sole actuator of anomalous time headway increase is noticeable.

Keywords: Roundabout, Entry capacity, Circulating flow, Follow-up time, Critical gap, Rainfall.