While seagull intersections can reduce traffic delays through their staged right-turn movements, their implementation has not always translated to improved safety outcomes. Studies have revealed increased crash rates at some seagull intersections. This can be attributed to two primary factors: compromised geometric design and inherent operational complexity.
Design issues include inadequate merge lane lengths, insufficient sightlines, or poorly defined turning areas. These can force drivers to execute challenging manoeuvres under time pressure, leading to increased collision risk. Additionally, the inherent complexity of the seagull layout, with its unique turning patterns and staggered traffic flows, can be cognitively demanding for unfamiliar drivers. This cognitive overload can contribute to confusion and misjudgement.
Waka Kotahi, the New Zealand Transport Agency, has developed a dedicated crash prediction tool for seagull intersections. This model quantifies the safety implications of various design elements, enabling engineers to optimise layouts.
The tool (and research report by Turner et al.) are available here: https://www.nzta.govt.nz/resources/research/reports/644/
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