Traffic safety engineering and crash analysis methods

Traffic safety engineering and crash analysis have played a critical role in advancing transportation systems by focusing on reducing fatalities, minimizing crash severity, and improving overall roadway conditions. This review compiles and interprets a broad spectrum of methodologies that have shaped the field in the United States, particularly those related to crash data acquisition, roadway geometric design, safety performance evaluation, and human factors integration. Emphasis has traditionally been placed on empirical approaches such as crash frequency models, empirical Bayes methods, and safety audits—tools that have provided a foundation for identifying high-risk locations and guiding countermeasure implementation. Various techniques have been developed to evaluate the safety implications of roadway elements including signalized and unsignalized intersections, freeway segments, and multi-lane urban corridors. Key frameworks such as Safety Performance Functions (SPFs) and Crash Modification Factors (CMFs) have become instrumental in quantifying safety outcomes and comparing the effectiveness of engineering treatments. These tools have evolved to better account for behavioral dynamics, spatial distribution of crashes, and site-specific roadway features, thereby supporting more accurate and meaningful safety assessments. Recent efforts have also focused on enhancing methodological rigor through advanced statistical tools, spatial analysis techniques, and refined use of disaggregated data. These developments contribute to a more detailed understanding of crash characteristics and roadway conditions. Complementing these methods are integrated data strategies that combine crash records, roadway inventory systems, and traffic exposure data to better isolate safety deficiencies and prioritize interventions. Additionally, there has been a growing shift toward proactive safety management, with approaches such as systemic analysis and surrogate safety assessments helping to identify risk factors before crashes occur. Evaluations of specific engineering solutions—including roundabouts, pedestrian hybrid beacons, median treatments, and complete street implementations—provide insights into the application and outcomes of such measures across different geographic and operational settings. A notable dimension of recent work is the inclusion of vulnerable road users, such as pedestrians and cyclists, and considerations of demographic and equity-based disparities in exposure and safety outcomes. This review consolidates foundational and evolving approaches within traffic safety engineering and crash analysis, offering transportation professionals and decision-makers a comprehensive understanding of current practices, tools, and applications aimed at improving road safety in the United States