The National Highway Traffic Safety Administration (NHTSA) estimates there was 38,680 fatalities resulting from vehicle crashes in 2020, and that fatalities continue to increase in the first half of 2021. To reduce fatal crashes, the Federal Highway Administration (FHWA) has adopted a Safe System Approach (SSA) that accommodates human error and understands that human bodies have limited ability to tolerate crash impacts. The SSA is bounded by six principles and five elements including safe roads, safe speeds, safe users, safe vehicles, and post-crash care. All five elements work congruently, while following the principles, to facilitate a safer and more accessible transportation paradigm for all users.
Historically, safety projects and policies have prioritized motorized vehicles over both pedestrians and bicyclists. Thus, fatal and serious injury crashes for pedestrians and bicyclists continued to grow across the country. To help improve these alarming numbers, the SSA has specifically identified elements (safe roads, safe users) and a principle (humans are vulnerable) that aims to prioritize and focus on users that are more vulnerable on the roadway network. The idea is that if we propose solutions that will provide vulnerable road users separation in time and space, the risk of yielding a serious or fatal injury crash will significantly diminish.
FHWA Safe System Solutions in Highway Safety Improvement Projects (HSIP)
The FHWA initiated a project to identify safe system solutions for highway safety improvement projects. As part of this project, B&N, in conjunction with Cambridge Systematics (CS), helped conduct an extensive literature review to identify safe system solutions, develop a safe system hierarchy of effectiveness, and created two framework alignments to support agencies in making better decisions when conducting projects and updating safety policies.
Safe System Hierarchy of Effectiveness
The Hierarchy of Effectiveness aims to provide safe system solutions that range from most effective to least effective. As part of this hierarchy, both “remove severe conflicts” and “conflict separation in time” focus on separation of vulnerable road users (VRUs) from motorists. Specifically, when considering “remove severe conflicts,” the literature review found that sidewalks and shared-use paths improve safety and mobility by providing pedestrians with dedicated space to travel, reducing potential collisions. Additionally, the literature review found that Leading Pedestrian Intervals (LPI) and Pedestrian Hybrid Beacons (PHB) help capture “conflict separation in time” by providing dedicated time to pedestrians where they are given protected priority within the roadway. These solutions can improve safety and create a transportation network that accommodates all users.
Project-Based Framework Alignment
A project-based alignment framework was created to prioritize countermeasures, strategies, and design elements that minimize severe injuries and are consistent with the Safe System Principles for the FHWA Office of Safety. The goal of the tool is to have practitioners/users evaluate projects through a safe system lens.
The framework measures the safe system alignment and determines how different types of improvements yield better levels of SSA alignment. It multiplicatively compounds crash exposure, crash risk, and crash likelihood to determine an overall safe system alignment measurement.
This alignment framework is unique in that application of safe system alignment measurement is calculated separately for VRUs and motorists. The measurement demonstrates that crash exposure, crash risk, and crash severity vary significantly between the two types of users and require different considerations and recommendations. By designing a framework that separates risks related to the types of users, we understand and consider that improvements and projects should view safety from varying perspectives.
In recent years, SSA has been a focus in safety discussions within the US and across the world; however, very little direction has been provided regarding implementation and measurement of Safe System Alignment. As such, B&N, along with CS and FHWA, are helping to define safe system solutions that align with the safe system approach and develop tools that will help local and state agencies make better informed decisions when conducting safety analysis.