The impact of shoulder characteristics on safety of highway in horizontal curves: a systematic literature review

Highway geometry has a significant impact on road safety, particularly in the shoulder of horizontal curves where vehicle dynamics and driver behavior are changed, and the likelihood of an accident is significantly higher. Highway safety is greatly impacted by shoulder characteristics because of the difficulties these road segments present. Improving road safety requires well-planned and regularly inspected highway shoulders. The association between shoulder characteristics and road traffic accidents has been the subject of several studies on ways to reduce crash rates. In this study, we reviewed the various research works, studied by researchers and discussed about how shoulder characteristics affect highway safety in horizontal curves. This article presents an analysis on the effects of several shoulder types on highway safety in horizontal curves, including shoulder width, shoulder rumble strips, inside or outside shoulders, part-time shoulder use (PSTU), hard shoulder running (HSR), and emergency shoulder use (ESU). This article also summarizes the benefits and limitations of these shoulder characteristics on highway safety. The results of this study demonstrated that the number of overall accidents has significantly decreased due to the implementation of all these shoulder characteristics on highways. This comprehensive analysis will give future researchers a better understanding when they do preliminary evaluations in the specific field.