Part-time Shoulder Use (PTSU) is a traffic management and operation strategy that allows the use of the left or right shoulder as a travel lane, typically during the peak hours of the day. Though PTSU is an effective strategy for increasing roadway capacity in congested traffic conditions, there is very limited quantitative information about PTSU design elements and operational strategy in the existing literature, which could impact the occurrence of crashes on freeways. This study contributes to the safety literature by analyzing various potential crash contributing factors related to PTSU operation and design elements through the development of short-term Safety Performance Functions (SPFs). A comparison of the estimated models demonstrated that by utilizing the mixed distribution and allowing the posterior parameter estimates of explanatory variables to vary from one observation to another, the Random Parameters Negative Binomial-Lindley (RPNB-L) model outperformed the traditional NB and fixed coefficient NB-L models. The results of the proposed RPNB-L model indicated that the PTSU implemented sections experienced a lower number of traffic crashes compared to the non-PTSU freeway sections. Among the attributes related to PTSU operation and design elements, the usage of the leftmost shoulder lane as PTSU, the presence of emergency rest areas for damaged vehicles, and adequate shoulder width would significantly reduce crash frequency for the PTSU implemented freeways. Moreover, investigation of the identified hotspots revealed that the transition areas (start/end locations of PTSU) are the most critical sections. The findings from this research could assist transportation agencies to take appropriate countermeasures for preventing and reducing crash occurrences on PTSU implemented freeways.

中文翻译：

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兼职肩部使用的随机参数负二项式-林德利模型的短期安全性能函数

部分时间路肩使用 (PTSU) 是一种交通管理和运营策略，允许通常在一天的高峰时段使用左路肩或右路肩作为行驶车道。尽管 PTSU 是在拥堵交通条件下增加道路通行能力的有效策略，但现有文献中有关 PTSU 设计元素和操作策略的定量信息非常有限，这可能会影响高速公路上碰撞事故的发生。本研究通过开发短期安全性能函数 (SPF)，分析与 PTSU 操作和设计元素相关的各种潜在碰撞影响因素，为安全文献做出贡献。估计模型的比较表明，通过利用混合分布并允许解释变量的后验参数估计随一个观测值而变化，随机参数负二项式-Lindley (RPNB-L) 模型优于传统的 NB 和固定系数模型NB-L 型号。所提出的 RPNB-L 模型的结果表明，与非 PTSU 高速公路路段相比，PTSU 实施路段的交通事故数量较少。在与 PTSU 操作和设计元素相关的属性中，使用最左侧的路肩车道作为 PTSU、为受损车辆设置紧急休息区以及足够的路肩宽度将显着降低 PTSU 实施的高速公路的碰撞频率。此外，对已识别热点的调查表明，过渡区域（PTSU 的起点/终点位置）是最关键的部分。这项研究的结果可以帮助运输机构采取适当的对策，预防和减少 PTSU 实施的高速公路上的碰撞事故发生。