Headway is a safety measure commonly used to investigate driving behaviour and driver performance. Its purpose is to reflect the following distance or time between a leading and following vehicle in traffic. It is therefore associated with drivers’ response time, such as in braking or swerving, during safety critical events. In the literature, distance and time headway are defined in different ways, despite standard definitions in the traffic engineering literature, which prompted this systematic review of headway definitions across a range of study designs, in order to recommend approaches to improve the accuracy and reproducibility of headway definitions used in road safety contexts. PRISMA guidelines were followed to search four databases (EMBASE, COMPENDEX, SCOPUS and MEDLINE) for studies that reported on headways or discussed methodological approaches. The search and filtering of abstracts identified 110 articles for a qualitative synthesis. Four broad approaches to measuring headways were detected: studies using simulation, roadside external features, on-road features, and on-vehicle features. Studies were coded as to whether they included written explanation, mathematical statements, or pictorial depictions of headway. Only 49.6% of studies contextualised headway sufficiently for reproducibility. Reproducibility is crucial for accurate interpretation of research findings and comparisons across studies. It is recommended that headway definitions should a) exclude vehicle or parts of vehicle lengths, b) include reference points (e.g., bumper/axle/rear), c) have a consistent terminology, and d) include the accuracy of headway measuring devices to report the precision of a study’s findings.

行驶距离是一种安全措施，通常用于调查驾驶行为和驾驶员表现。其目的是反映行进中的先行车辆与后行车辆之间的跟随距离或时间。因此，它与驾驶员在安全关键事件中的响应时间（例如制动或转弯）相关。在文献中，尽管交通工程文献中有标准定义，但距离和时程的定义却以不同的方式进行，这促使系统地回顾了一系列研究设计中的时程定义，从而提出了改进方法的准确性和可重复性的建议。道路安全环境中使用的车距定义。遵循PRISMA指南搜索四个数据库（EMBASE，COMPENDEX，SCOPUS和MEDLINE），用于进行进展报道或讨论方法论的研究。摘要的搜索和过滤确定了110篇文章以进行定性综合。检测到四种测量车头距离的方法：使用模拟进行研究，路边外部特征，道路特征和车辆特征。研究被编码为包括书面解释，数学陈述或前进的图画描述。只有49.6％的研究充分说明了可重复性的进展。可重复性对于准确解释研究结果和研究之间的比较至关重要。建议车距定义应a）排除车辆或部分车辆长度，b）包括参考点（例如，保险杠/车轴/后方），c）具有一致的术语，