Department of Civil and Environmental Engineering, 107 McLaughlin Hall, University of California, Berkeley, Berkeley, CA 94720, USA.
Institute for Choice, University of South Australia, Level 13, 140 Arthur Street, North Sydney, NSW 2060, USA.
J Safety Res. 2021 Dec;79:135-147. doi: 10.1016/j.jsr.2021.08.014. Epub 2021 Sep 15.
Safety is a critical factor in promoting sustainable urban non-motorized travel modes like bicycles. Helmets have shown to be effective in reducing injury severity in bicycle crashes, however, their effects on bicyclists' behaviors still requires deeper understanding, especially amid the emerging trend of using shared bicycles. Risk compensation effects suggest that bicyclists may offset perceived gains in safety from wearing a helmet by increasing risk-taking behaviors. A better understanding of these compensation effects can be useful in assessing various bicycle safety related programs.
Using a sample of 131 bicyclists from the San Francisco Bay area, this research studies how bicyclists respond with respect to risk-taking behaviors under various urban-street conditions, as a function of helmet use. Study participants were each shown 12 videos, shot in Berkeley, California, from the perspective of a bicyclist riding behind another bicyclist. A fractional factorial experiment design was used to systematically vary contextual attributes (e.g., speed, bike lane facilities, on-street parking, passing vehicles) across the videos. After each video, participants were asked to indicate if they would overtake the bicyclist in the video. With the help of data adaptive estimation techniques, targeted maximum likelihood estimation (TMLE) was applied to estimate the average risk difference between helmeted users and non-users, controlling for self-selection effects. Individual-based nonparametric bootstrap was performed to assess the uncertainty associated with the estimator.
Our findings suggest, on average, individuals more likely to wear a helmet are 15.6% more likely to undertake a risky overtaking maneuver. Practical Applications: This study doesn't try to oppose mandatory helmet laws, but rather serves as a cautionary warning that road safety programs may need to consider strategies in which unintended impact of bicycle helmet use can be mitigated. Moreover, our findings also provide additional evaluation component when it comes to the cost-benefit assessment of helmet-related laws.
安全是促进可持续城市非机动出行方式（如自行车）的关键因素。头盔已被证明可有效降低自行车事故中的伤害严重程度，但它们对自行车骑行者行为的影响仍需要更深入的了解，尤其是在共享自行车这一新兴趋势下。风险补偿效应表明，自行车骑行者可能会通过增加冒险行为来抵消戴头盔带来的安全感提升。更好地理解这些补偿效应有助于评估各种与自行车安全相关的项目。
本研究使用来自旧金山湾区的 131 名自行车骑行者的样本，研究了在各种城市街道条件下，头盔使用情况如何影响自行车骑行者的冒险行为。研究参与者每人观看了 12 个视频，这些视频是从加利福尼亚州伯克利市的一名自行车骑行者从后面追赶另一名自行车骑行者的视角拍摄的。使用分因子实验设计，系统地在视频中变化情境属性（例如，速度、自行车道设施、路侧停车、过往车辆）。观看完每个视频后，参与者被要求表明是否会超越视频中的自行车骑行者。在数据自适应估计技术的帮助下，应用靶向最大似然估计（TMLE）来估计头盔使用者和非使用者之间的平均风险差异，同时控制自选择效应。进行个体基于的非参数自举来评估估计量的不确定性。
我们的研究结果表明，平均而言，更有可能戴头盔的个体更有可能采取冒险的超车行为，其可能性增加了 15.6%。
本研究并非试图反对强制性头盔法，而是提醒道路安全计划可能需要考虑一些策略，以减轻自行车头盔使用的意外影响。此外，我们的研究结果还为评估与头盔相关的法律的成本效益提供了额外的评估内容。
