APPENDIX

Summary of Current Diagnostic Assessment and Countermeasure Selection Tools for Crashes

1 Introduction

This subsection reviews diagnostic assessments and countermeasure selection approaches used to assess and mitigate roadway crashes. This is a substantial field, and the goal was not to capture every instance of these methodologies; rather, it was to generally present the breadth and nature of the current state of the art of diagnostic assessment and countermeasure selection. The following resources are presented and described as follows:

• Program Evaluation
• Highway Safety Manual (HSM)
• usRAP (Roadway Safety Foundation, 2024b)
• Systemic Safety Project Selection Tool
• Safe System
• PEDSAFE (FHWA, n.d.c) and BIKESAFE (FHWA, n.d.a)
• Field Guide for Selecting Countermeasures at Uncontrolled Pedestrian Crossing Locations (Blackburn et al., 2018)
• Use of naturalistic driving study (NDS) data

2 Program Evaluation

State highway safety plans (e.g., SHSPs) use safety data—such as fatal crashes and crashes involving serious injuries along with roadway and traffic data—to identify critical highway safety problems and safety improvement opportunities. These plans include specific multi-year goals, objectives, and measures to support performance-based highway programs. Specific strategies for improving safety include the highway safety elements of engineering, education, enforcement, and emergency services (the four “E’s”; FHWA, 2016).

From FHWA (2016): “For example, if speed is an emphasis area in a State SHSP, the State may consider a variety of 4 E strategies to reduce or mitigate the impact of speeding. Strategies might include increasing law enforcement efforts to reduce speeding (enforcement), applying traffic calming measures such as speed humps and roundabouts (engineering), delivering public

information campaigns that focus on the dangers of speeding (education), and utilizing Emergency Medical Services data to quantify the burden to the health care system and the cost to the community (emergency services).”

Equally critical to improving safety performance is the evaluation (the fifth “E” of safety) of crash data in modal and facility contexts to assess and aid the selection and design of countermeasures. While program evaluation might be considered something to worry about after countermeasures have been identified, this fifth “E” should be implemented at every stage of the safety improvement process (see Figure 1) and include input and involvement from the range of transportation professionals involved, including planners, designers, engineers, and safety analysts. In short, having an evaluative mindset throughout the crash prevention process can add rigor and purpose to safety improvement planning. Evaluation is simply the process of examining the value or worth of something. In the highway safety context, evaluations focus on rigorously analyzing and assessing the efficacy of safety improvements to determine what is working and why. As described in Pullen-Seufert and Hall (2008), evaluations should be seen as a tool to be used throughout the highway safety improvement process to clarify problems, help develop good safety questions, prioritize countermeasures, identify metrics for success, and then assess countermeasure implementations. At its most fundamental level, countermeasure evaluations focus on two basic questions: (1) did you implement the program as planned? and (2) did you accomplish your objectives? (Pullen-Seufert and Hall, 2008).

Pullen-Seufert and Hall (2008) provide a seven-step process for evaluating highway safety programs and countermeasures, as follows:

1. Identify the problem: Gather and analyze the information necessary to help determine the nature and size of the problem you wish to address, data on contributing factors, where the problem is manifesting, and who is being affected.
2. Develop reasonable objectives: What will determine the success of a proposed program, treatment, or countermeasure, and how will success be measured? Program objectives should be SMART (specific, measurable, action-oriented, reasonable, and time-specific) (Pullen-Seufert and Hall, 2008).
3. Develop a plan for measuring results: Develop a detailed plan that describes what you will measure, how you will measure it, and how you will analyze the results obtained. In general, evaluations are more robust when they include multiple measures obtained from multiple methods—it is beneficial to consider a range of outcome measures that are appropriate to your evaluations. For example, a countermeasure to reduce speeding behavior might use speeding-involved crashes, speeding tickets, and surveys of public awareness to assess efficacy.
4. Gather baseline data: Measuring the value of a proposed program, treatment, or countermeasure often includes comparing measured outcomes before implementation to those same outcomes after implementation, while controlling for other key variables that could impact the results.

5. Implement your program: Initiate the program, treatment, or countermeasure that is the focus of your evaluation and document all implementation issues, questions, or milestones that might be important as you analyze your data.
6. Gather data and analyze results: Data collection and analysis may well be the most complex and labor-intensive elements of an evaluation. In this regard, a data collection schedule with detailed procedures should be developed and followed. Pay close attention to any external events that could change your outcomes in ways that are separate from the program, treatment, or countermeasure under evaluation. For example, if you are monitoring the effects of a countermeasure to reduce speeding behavior through a specific section of roadway and that roadway undergoes a major revision involving work zones and reduced traffic and throughput, you may wish to delay the evaluation or shift the implementation to another roadway to avoid confounding the results.
7. Report results: Clearly communicate the objectives, methods, results and conclusions of your evaluation to all organizations involved in the effort.

3 Highway Safety Manual

The American Association of State Highway and Transportation Officials (AASHTO) HSM is a resource that provides safety knowledge and tools in a useful form to facilitate improved decision-making based on safety performance (AASHTO, 2010). The six steps of the roadway safety management process are presented in Figure 1 in this appendix and are described in this section. The inputs and outputs for each step vary based on the safety management approach employed. The six-step roadway safety management process helps agencies develop a prioritized list of safety improvement projects and then evaluate the effectiveness of the projects in reducing crash frequency and/or severity.

1. Network Screening—Review a transportation network to identify and rank individual sites based on the potential for reducing crashes.
2. Diagnosis—Evaluate crash data, historic site data, and field conditions to identify crash patterns of interest at each site.
3. Countermeasure Selection—Identify factors that may contribute to crashes at a site and select possible countermeasures to reduce crashes.
4. Economic Appraisal—Calculate the estimated benefits and costs of potential countermeasures and identify individual projects that are cost-effective or economically justified.
5. Project Prioritization—Evaluate economically justified improvements at specific sites and across sites to identify a set of improvement projects that meet objectives such as cost, mobility, or environmental impacts.
6. Safety Effectiveness Evaluation—Evaluate the effectiveness of a countermeasure, a combination of countermeasures, or projects implemented at multiple sites in reducing crash frequency and/or severity.

The roadway safety management process may be conducted sequentially as described, or each step may be conducted in isolation. This project focused on Steps 2 and 3 of the roadway safety management process. As noted above, however, the fifth E—evaluation—should be applied throughout the entire process.

The three primary steps associated with diagnosis outlined in the HSM are as follows (AASHTO, 2010):

1. Review safety data such as crash types, severities, and environmental conditions to develop descriptive statistics and identify crash patterns.
2. Review supporting documentation, such as past studies and plans covering the site vicinity, to identify known issues, opportunities, and constraints.
3. Conduct a field investigation to assess the conditions of the site and observe how different users and modes travel through the site and use available facilities and services in the vicinity of the site.

The HSM describes the three primary steps of countermeasure selection (AASHTO, 2010):

1. Identify factors contributing to the cause of crashes at the subject site.
2. Identify countermeasures that may address the contributing factors.
3. Conduct a cost-benefit analysis, if possible, to select preferred treatments.

Although the HSM has several different types of documentation—including user guides—to assist with understanding the approach, the tools may be difficult for some to navigate. For example, the diagnostic process includes human factors as an integral component of its procedure; however, the HSM lacks a systematic and fully guided approach to human factors insofar as there does not exist a checklist or set of detailed diagnostic questions related to specific human factors issues. Such a tool that maintains a level of specificity would be beneficial. Rather than relying on the users to understand what features fall under each human factors category, users will be able to simply be guided by the tool itself.

4 usRAP

The usRAP is a free and proactive safety management tool used to rate the safety of a roadway based on an assessment of the presence and condition of the roadway, roadside, and intersection design elements and to identify cost-effective countermeasures to reduce fatal and serious injury crashes (Roadway Safety Foundation, 2024b). This tool is used by state and local highway agencies, and each agency’s data are password protected. The usRAP is not meant to take the place of professional engineering studies, RSAs, or other activities carried out by roadway agencies and traffic engineers; but, this data-driven tool provides proactive procedures to assess crash potential, mapping capabilities, and cost-benefit considerations to identify cost-effective countermeasures to reduce fatal and serious injury crashes (Roadway Safety Foundation, 2024a).

Data for roadway networks are collected and inputted into a software package that assigns a star rating (from one to five), reflecting the socioeconomic cost of crashes on the particular road section. The data needed for the software may be acquired from existing highway agency databases. When these data are unavailable, the required data input may be coded from Internet-based roadway photos or video logs.

The tool can be used to perform two types of analysis: developing star ratings and developing safer road investment plans. Star ratings and safer road investment plans are developed for 328-ft (100-m) sections of roadway, combined to provide recommended improvements for specific road sections, entire routes, and entire road networks.

Star ratings provide insight into crash likelihood and crash protection. Star ratings are based on the presence or absence of design and traffic control features associated with safety on an area of a roadway. A rating of one star indicates a road has few safety-related design and traffic features, whereas a rating of five indicates a road has many safety-related design and traffic features. Separate star ratings are provided for vehicle occupants, bicyclists, pedestrians, and motorcyclists because features that affect crash frequencies for these different modes of travel are very different.

After star ratings are assigned, the software evaluates approximately 70 countermeasures for potential implementation. If there appears to be an engineering need for a countermeasure and that countermeasure is not already present on the roadway segment, the countermeasure is identified for consideration in an economic analysis, and the software performs a cost-benefit

analysis for every countermeasure that was identified during the process. This output is referred to as a safer roads investment plan. Although site-specific crash data are not required, crash data are highly recommended for appropriate calibration to local conditions. The safer roads investment plan considers estimates of how many lives could be saved over 20 years if each improvement specified by the plan was made.

According to the usRAP website, this tool is user-friendly in that it does not require extensive crash data and, instead, uses aerial photos or video logs and free online software to generate a safer road investment plan (Roadway Safety Foundation, 2024a). Furthermore, the usRAP protocols and video software are available for free. The usRAP trainings may also be accessed free of charge. However, acquiring all of the required elements to utilize usRAP may be time-consuming. Additionally, the mention of human factors is absent from their website and other associated documentation. The software selects the use of potential countermeasures automatically without taking into consideration contributing factors of the crashes.

5 Systemic Safety Project Selection Tool

The Systemic Safety Project Selection Tool is used by state and local highway agencies and transportation planning organizations (Preston et al., 2013). The aim is to assist agencies with performing a systemwide evaluation—rather than site-specific analyses—to identify roadway features common to locations with a crash history; this process enables agencies to proactively address crashes that are widely dispersed across a highway and is considered more beneficial for countermeasure development versus diagnosing individual crashes (Preston et al., 2013).

Similar to the HSM, this tool presents a cyclical safety management process that involves three elements:

1. The Systemic Safety Planning Process helps analysts identify priority crash types and associated crash contributing factors, evaluate proven, low-cost safety countermeasures, and prioritize candidate locations for improvement.
2. A Framework for Balancing Systemic and Traditional Safety Investments that helps set funding goals between systemic and traditional safety programs.
3. Program Evaluation Methods that provide high-level direction for evaluating the effectiveness of systemic safety programs.

Of the three elements, the systemic safety planning process addresses diagnosis and countermeasure selection at various levels. The systemic safety planning process begins by identifying focus crash types, facility types, and contributing factors. The next steps involve documenting and/or identifying the most common characteristics of the locations where each focus crash type occurred and developing a prioritized list of potential locations on the roadway system that could benefit from systemic safety improvement projects. The data required to establish this include observations of site-specific crash information and basic features of the road system. Once facility types are identified, the factors contributing to roadway crashes along the network and at specific locations are assessed. The outcome of this process is an assessment and ranking of the focus facility elements in terms of their priority for safety improvement. The

next stage of the safety planning process involves assembling a list of potential countermeasures, screening and evaluating said countermeasures, and selecting the countermeasures for deployment. This step involves assembling a small number of low-cost, highly effective countermeasures to be considered for project development at candidate locations.

Overall, this diagnostic tool is flexible (applicable to various systems, locations, and crash types), easy to use (requires minimal training and assistance), and easy to understand (the output is understandable by program managers and development engineers). Regarding the steps involving diagnosis and countermeasure selection, little guidance is provided in terms of how to select countermeasures to address the crash-contributing factors. In addition, the inclusion of human factors is minimal, as this tool only tends to mention poor visibility and excessive speed as potential crash-contributing factors (Preston et al., 2013).

6 Safe System

The Safe System approach is a worldwide movement implemented since the 1990s (Signor et al., 2018; Welle et al., 2018) via programs such as Vision Zero in Sweden and other countries. According to the Federal Highway Administration (FHWA), the Safe System approach is one way to reduce deaths and serious injuries on the road (Welle et al., 2018; Finkel et al., 2020). The World Health Organization has expressed a similar perspective of the approach, but with a particular emphasis on human involvement, as it has stated that the goal of Safe System is to ensure that if crashes occur, humans are not seriously injured (Finkel et al., 2020).

The Safe System approach has been claimed to encompass an interaction of issues that lead to roadway deaths and injuries; that is, it prioritizes the protection of VRUs (e.g., pedestrians and cyclists) and emphasizes the responsibility of roadway system designers (Welle et al., 2018). For example, the Safe System approach would contend that humans make mistakes and are fragile and vulnerable. Consequently—to address roadway issues—one aim of a Safe System approach would be to reduce the need and length of driving trips (Finkel et al., 2020). Furthermore, Safe System emphasizes the importance of designing and operating transportation systems that are “human-centric” and accommodate such vulnerabilities (e.g., managing kinetic energy transfer within survivable limits to inform the design and operation of the road system).

The areas that Safe System focuses on are motivated by six core principles (Signor et al., 2018; Welle et al., 2018; Finkel et al., 2020):

1. Death/serious injury is unacceptable.
2. Humans make mistakes/errors.
3. Humans are vulnerable to injury.
4. Safety is proactive.
5. Responsibility is shared.
6. Redundancy is crucial.

As a result of these motivating principles, the Safe System approach aims to integrate five elements to promote a safe transportation system, the first of which is safe road users who comply with the rules of the road. Compliance is demonstrated by behaviors such as paying attention and adapting to changing conditions. The second is having safe vehicles on the road that are equipped with appropriate safety features (e.g., airbags, seatbelts) and an effective design. Others include promoting safe speeds and roads and the final deals with post-crash care (e.g., providing emergency services and crash/reporting investigation) (Finkel et al., 2020).

In addition to promoting the importance of the human in the process of enhancing roadway safety, the Safe System approach also emphasizes several other factors that are purportedly integral to mitigating issues on the road. One such factor is that responsibility is shared by various stakeholders (e.g., road users and system managers), who work together to provide safety countermeasures (Finkel et al., 2020). Furthermore, the approach underscores proactive tools to identify and mitigate crash potential on the roadway system and redundancy so that if something fails, there will exist other parts to mitigate crash potential (Finkel et al., 2020). These factors interact with human factors, such as, for example, implementing redundancy via rumble strips to alert a drowsy or distracted driver (Finkel et al., 2020). There still exists, however, a lack of clear attention on human factors, such as visibility and time perception, and clear, actionable items or strategies that may be utilized to directly target a wide variety of human factors characteristics. Indeed, it is clear that more attention must be focused on bridging the gap between theoretical strategies implied by the Safe System approach and current practices.

7 PEDSAFE and BIKESAFE

PEDSAFE (FHWA, n.d.c) and BIKESAFE (FHWA, n.d.a) are intended primarily for use by engineers, planners, safety professionals, and decision-makers, but they may also be used by citizens for identifying problems and recommending solutions for their communities associated with walking and biking. PEDSAFE and BIKESAFE are online tools intended to provide the most applicable information for identifying safety and mobility needs and improving conditions for pedestrians and bicyclists within the public right-of-way. These tools are designed to enable practitioners to select engineering, education, and enforcement countermeasures to help mitigate known crash problems and/or to help achieve a specific performance objective. The tools

• Provide information about pedestrian and bicycle crash types, statistics, and other background resources;
• Provide users with information on what countermeasures are available to prevent specific categories of pedestrian and bicycle crashes or to achieve certain performance objectives;
• Outline considerations to be addressed in the selection of a countermeasure;
• Provide a decision process to eliminate countermeasures from the list of possibilities; and
• Provide case studies of countermeasures introduced in communities throughout the United States.

These tools have several options for selecting potential countermeasures. There is an interactive selection tool that allows the user to develop a list of possible countermeasures based on site characteristics, such as geometric features and operating conditions and the type of safety problem or desired behavioral change. The user first inputs information about the location of the site. Then, the user must decide on the goal of the treatment. It may either be to achieve a specific performance objective, such as reducing traffic volumes or mitigating a specific type of pedestrian/bicycle collision. Once a specific goal has been selected, the analyst provides answers to a series of questions related to the geometric and operational characteristics of the site. The answers are used to narrow the list of appropriate countermeasures for a specific goal.

Another option for selecting potential countermeasures is through the use of interactive matrices that provide the user with a quick view of the relationship between performance objectives and several countermeasure groups or the relationships between several crash types and countermeasure groups. In either matrix, a filled cell indicates that there is a specific countermeasure within the countermeasure group, this applies to the performance objectives or crash types. From there, the analyst can choose to select a countermeasure and be linked to the countermeasure description.

Overall, these tools are easy to use and accessible online via the FHWA’s Pedestrian Safety Guide and Countermeasure Selection System (PEDSAFE) (FHWA, n.d.c). These tools are also incorporated in the Pedestrian and Bicycle Crash Analysis Tool (FHWA, 2023c). With each countermeasure included in the tools, a description of the treatment is provided along with its purpose, other considerations that one should be aware of, and cost estimates. The inclusion of human factors considerations is minimal.

7.1 Guide for Selecting Countermeasures at Uncontrolled Crossing Locations

The Field Guide for Selecting Countermeasures at Uncontrolled Pedestrian Crossing Locations (Blackburn et al., 2018) helps agencies select crash countermeasures based on criteria established in published literature, best practices, and national guidance. The tool describes a comprehensive decision-making process for the installation of pedestrian crossing countermeasures and leads an agency through the process. The steps involve

• Collecting data and engaging the public,
• Collecting an inventory of the site conditions and prioritizing locations,
• Analyzing crash types and safety issues,
• Selecting countermeasures,
• Consulting design and installation resources, and
• Identifying opportunities and monitoring outcomes.

The tool focuses on selecting countermeasures at uncontrolled crossing locations—where sidewalks or designated walkways intersect a roadway where no traffic control (i.e., traffic signal or stop sign) is present. The countermeasures described in the tool include

• Crosswalk visibility enhancements,
• Raised crosswalks,
• Pedestrian refuge islands,
• Pedestrian hybrid beacons, and
• Road diets.

The Field Guide for Selecting Countermeasures at Uncontrolled Pedestrian Crossing Locations (Blackburn et al., 2018) describes each countermeasure and presents additional design and installation considerations, such as references to the Manual on Uniform Traffic Control Devices (MUTCD) (FHWA, 2009).

This tool presents two tables for a practitioner to identify potential countermeasures. The first table (Application of Pedestrian Crash Countermeasures by Roadway Feature) identifies suggested countermeasures for uncontrolled crossing locations according to roadway and traffic features. Features addressed in the table include the number of lanes, median type, speed limit, and traffic volumes. The second table (Safety Issues Addressed per Countermeasure) compares crash types and other observed safety issues to the countermeasures. The safety issues addressed within this table include conflicts at crossing locations, excessive vehicle speed, inadequate conspicuity/visibility, drivers not yielding to pedestrians in crosswalks, and insufficient separation from traffic.

The Field Guide for Selecting Countermeasures at Uncontrolled Pedestrian Crossing Locations is relatively simple to use. A field guide is available that provides instructions on how to use the tables and a sample inventory form for agencies to record information about roadway characteristics, and safety issues and descriptions of the countermeasures are provided.

7.2 Use of Naturalistic Driving Study Data

NDSs offer great potential to help identify and prioritize contributing factors to crashes, and for supporting countermeasure development and assessments; to date, such studies have been extremely valuable in clarifying how driver performance and behavior affect the potential of roadway crashes (Victor et al., 2015). One such study is the 100-Car NDS sponsored by the NHTSA and the Virginia Department of Transportation (Dingus et al., 2006). According to Dingus et al. (2006), the “100-Car Naturalistic Driving Study is the first instrumented vehicle study undertaken with the primary purpose of collecting large-scale naturalistic driving data” (p. xxii). The NDS was unobtrusive in that participants were asked to freely drive as they typically would, thereby creating a database of naturalistic driver behaviors, such as aggressive driving, drowsiness, judgment error, and so forth (Dingus et al., 2006). Additionally, the naturalistic nature of the study provides information about pre-crash and crash events that are externally valid (Dingus et al., 2006).

Indeed, in a report that conducted analyses of driver inattention using the driving data that were collected from the 100-Cars NDS, the results revealed that driving while drowsy led to a higher probability of a near-crash/crash risk compared to alert drivers and that drivers who engage in visually and/or manually complex tasks also have a higher probability of near-crash/crash risk than those who are attentive (Klauer et al., 2006). Not only did the NDS data reveal human factors that increase near-crash/crash risk, but it also clarified environmental factors that heighten the probability of such risk. For instance, the data showed that driving while drowsy is more dangerous when passing through intersections, wet roadways, and high-traffic areas (Klauer et al., 2006). NDSs have also revealed how driving context influences a driver’s decision to partake in visual-manual phone tasks (i.e., texting, dialing, reading) (Tivesten and Dozza, 2015).

As a further example, consider the problem of red-light running at intersections. One cause of red-light running occurs when drivers have difficulty deciding whether to stop at the stop line or proceed through the intersection as they approach a traffic signal that recently changed from green to yellow. Often in this situation, a “dilemma zone” is created if the vehicle is too close to stop safely before the stop-line but too far away to clear the intersection before the signal changes to red (for a more detailed discussion of the dilemma zone, see Campbell et al., 2012). A wide range of situational factors affects driver behavior in a dilemma zone situation and red-light running. In dilemma zones, these include factors such as yellow duration, cycle length, surrounding vehicle actions, approach speed, driver age, and gender, among several other factors. Yet, approaches for calculating dilemma zones typically only include basic variables such as vehicle speed measures, distance, and driver response time. While the concept of the dilemma zone is relatively simple and is often treated as such, the environmental, situational, and driver aspects underlying the decision to stop or run a yellow/red light are substantially more complex. NDS data, such as data obtained from the Strategic Highway Research Program 2 (SHRP 2) (AASHTO, n.d.a) can provide answers to the following questions:

1. What are the circumstances surrounding red-light running, and what immediate situational factors (e.g., roadside distraction, lead vehicle going, high pedestrian traffic volume, and so forth) are associated with this behavior?
2. What is the relationship between the calculated dilemma zone for an intersection and what drivers actually do? What driver, situational, location-specific, and environment factors (see Table 1) are associated with drivers, making them lead to crashes or increased crash potential? How do these driver decisions/actions vary across intersections with different characteristics?
3. How do drivers respond to dilemma zone situations? What factors incline drivers to stop or to go at yellow onset (e.g., signal timing, signal visibility, driver attention, and so forth)?

Specifically, NDS data like the SHRP 2 data provide a unique opportunity to examine driver red-light running and dilemma zone behavior by providing a detailed picture of the driving situation and driver actions leading up to an intersection immediately before the traffic signal changes, including several types of data that can be extracted from the SHRP 2 driving and roadway data files (see Table 1).

Table 1. Variables from the SHRP 2 data set relevant to studying dilemma zone behaviors.

A particularly valuable feature of the SHRP 2 NDS data is that the listed variables are generally available for each traversal of an intersection, which provides an opportunity to take a comprehensive and holistic look at driver behaviors in dilemma zones, in contrast to the other studies that typically only examine a small number of these variables at a time. Taken together, these examples demonstrate how NDS data can elucidate particular human and environmental factors that influence roadway crash risk and, therefore, have implications for which areas to consider when developing diagnostic and countermeasure resources.