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A number of alternative intersection layouts are used around the country to reduce traffic delays and to improve road safety. One such group of alternative intersections are termed ‘priority controlled seagull intersections’.

Seagull intersections are often used on roads to reduce traffic delays as they allow right-turning traffic from the side road to give way to traffic flow on the main road one direction at a time (without impeding the through traffic). However a number of seagull intersections experience high crash rates. This can be a result of design compromises (e.g. short merges) and/or due to the complexity and unfamiliarity of this intersection layout.

While there is considerable debate about the safety problems that occur at seagull intersections and left-turn slip lanes at priority intersections, there has been very little research that attempts to quantify the safety impact of different layouts.

In New Zealand, crash prediction models are available for urban and rural priority controlled intersections of a standard layout.

In this study, crash prediction models have been developed in an attempt to quantify the effect of various seagull intersection and left-turn slip lane designs.

Keywords: channelised layouts, crash modifying factors, crash prediction models, left turn slip lanes, priority intersections, right turn slip lanes, safety performance functions, seagull layouts, T-intersections