Expanding Crash Data Analysis

Expanding Crash Data Analysis: Defining Crash Risk for Non-Motorized Users

Daniel Capparella / Jessica Hill, AICP, PMP / Ashleigh Glasscock

DANIEL CAPPARELLA has been with GNRC since August of 2019. He currently serves as the Active Transportation Planner and coordinates the bike and pedestrian elements of transportation planning carried out by the organization. Prior to joining GNRC, he worked at the Los Angeles Community Action Network, a homelessness advocacy organization in the Skid Row Community and greater Los Angeles metropolitan area. He earned a Bachelor of Arts in urban and environmental policy from Occidental College.

JESSICA HILL serves as the community and regional planning director for the Greater Nashville Regional Council. With more than 14 years of experience in local and regional government, Jessica excels at building partnerships across government and business sectors. She holds a Master of City and Regional Planning from the University of North Carolina at Chapel Hill and Master of Business Administration from Wake Forest University.

ASHLEIGH GLASSCOCK has been with GNRC since December 2018. She serves as a senior research analyst, working to assess a variety of datasets, create maps, data visualizations, and perform data analysis in support of GNRC’s programs. She helps support programs related to demographics, development, infrastructure, natural resources, and quality of life. Prior to joining GNRC, she attended East Tennessee State University where she received her master’s degree in geoscience with a concentration in geospatial analysis.

ABSTRACT

Problem Approach and Finding

The Nashville region has a troubling trend. Since 2015, pedestrian fatalities have almost doubled. While serious motorized injuries were nearly cut in half, non-motorized serious injuries remained constant. These trends have worsened during the COVID-19 pandemic. With the recent surge in active transportation activity in the region and limited funding available for bicycle and pedestrian improvements, a more systemic and focused approach must be utilized to identify and prioritize solutions for improving safety for bicyclists and pedestrians.

This article presents a non-motorized risk index that provides a system-level tool to proactively identify areas with unsafe nonmotorized conditions to better guide planning and prioritize solutions for bicyclists and pedestrians.

Implications

By demonstrating the ability to identify unsafe conditions for bicyclists and pedestrians across the Nashville region’s transportation network beyond a hot spot analysis, this index can help inform future investments that improve safety for all users of the transportation network and provide a framework to expand areas considered for non-motorized safety improvements.

INTRODUCTION

The built environment, which includes the transportation network that facilitates movement and mobility, is a foundation of community health. The transportation network is intended to accommodate multiple transportation modes, but traditional roadway design inequitably favors vehicle throughput over non-motorized needs.

In 2019, 6,205 pedestrians were killed in traffic crashes in the United States. (USDOT National Highway Traffic Safety Administration 2020) That is about one death every 85 minutes. In the same year, 846 bicyclists were killed in traffic crashes in the United States. (USDOT National Highway Traffic Safety Administration 2020) Similar to national trends, the Nashville region is experiencing a troubling trend for non-motorized safety. Since 2015, pedestrian fatalities have almost doubled and while serious motorized injuries were almost cut in half, non-motorized serious injuries remained constant. These trends have worsened during the COVID-19 pandemic. Data from the Tennessee Department of Safety reveals that 2020 proved to be the worst year on record as pedestrian fatalities continue to rise even with less cars on the road. (Tennessee Highway Patrol n.d.) With the recent surge in active transportation activity in the region due to COVID-19 related behavior patterns, combined with limited funding available for bicycle and pedestrian improvements, it is imperative that a more systemic and focused approach be utilized to identify and prioritize solutions to improve safety for bicyclists and pedestrians.

BACKGROUND

Crash data has traditionally been used to identify dangerous areas for bicyclists and pedestrians and to make investments in safety improvements through location specific crash analyses or hot-spot analyses. Yet, relying solely on prior crashes is limiting because it does not capture all areas that are unsafe for non-motorized users. Given that bicyclists and pedestrians often avoid areas without facilities or suitable conditions, there are unsafe locations not represented through a traditional crash analysis. To better understand the factors that result in nonmotorized crashes in the Nashville region, the Greater Nashville Regional Council (GNRC) developed a non-motorized risk index to systematically identify unsafe locations for bicyclists and pedestrians.

GNRC is the federally designated metropolitan planning organization (MPO) for the Nashville region and is responsible for investing in transportation improvements, preparing, and maintaining a long-range transportation plan, and planning and programming federal, state, and local funds for transportation projects and operations. Every five years GNRC updates the Regional Transportation Plan (RTP) to account for shifts in national policy, local community issues and concerns, travel behaviors, advancements in technologies, and fluctuations in funding availability. (The Greater Nashville Regional Council 2021)

In 2019, GNRC began the process of updating the 2045 RTP and identified that prior RTPs had limited investment for bicycle and pedestrian infrastructure. An increase in bicycle and pedestrian fatalities and population and shifts in lifestyle preferences for more walkable communities led to a more comprehensive way to identify and prioritize areas for non-motorized safety improvements. The purpose was to develop a tool for prioritizing areas for investment in non-motorized safety across the region.

The non-motorized risk index aims to capture unsafe areas (beyond where crashes occur) at the system level based on an analysis of crash risk factors related to the built environment, common destinations, and travel behavior. The index identifies areas where the odds of non-motorized crashes occurring are disproportionately high. The index can help proactively identify locations with unsafe non-motorized conditions to better guide safety planning and improvements in the Nashville region through a rough system-level approach.

OVERVIEW OF THE DEVELOPMENT OF NONMOTORIZED RISK INDEX

The index was developed through a set of five steps. Each step includes a corresponding question that is answered by the step below. While each step answers a prompt question, the index includes the following five steps to drill down to a system level to understand what increases crash risk across the entire region, not only in areas where crashes have occurred. Figure 1 details the index development process starting with the baseline: the regional hot-spot analysis.

HOT-SPOT ANALYSIS BASELINE

The baseline of this index stems from a traditional hot-spot analysis, shown in Figure 2 below, which identified high-crash areas based on prior bicycle and pedestrian crash history between 2015 and 2019 across the region. This step of the analysis was conducted for the update to the RTP and used to inform regional project evaluation. While the hotspot analysis indicates areas that are unsafe based on past crashes, it does not capture all unsafe areas across the region, including those that have not experienced crashes. To better understand factors that may be contributing to crashes, staff examined common characteristics of those locations.

Figure 2: Non-Motorized Crash Hot-spots 2015– 2019 (TITAN Database)

Step 1: Identification of Common CharacteristicsTo better understand what characteristicsare present at high-crash areas, a sample often hot-spot locations, five for pedestriansand five for bicyclists, were reviewed toobserve common characteristics associatedwith bicycle and pedestrian crashes. Theselocations and the characteristics associated with them are significant because they represent roadway design elements, common destinations where pedestrians and bicyclists typically frequent, and travel behavior that increase exposure of pedestrians and bicyclists to motor vehicles across the network, which creates the foundation for a more in-depth analysis to identify factors that increase the risk for a non-motorized crash to occur.

Step 2: Identifying Risk Factors Common characteristics of crash locations were identified that could be quantified through available datasets, resulting in eleven risk factors. The risk factors were sorted into groups based on their relationship to the built environment, common destinations, and travel behavior.

Step 3: Analyzing Crash Risk Factors Each of the eleven risk factors were analyzed to determine trends in non-motorized crashes. For example, vulnerable populations, which is one of the risk factors, account for a minority of the region’s population. The analysis found that six of the nine vulnerable populations, despite being a minority of the total population, account for a disproportionally high percentage of non-motorized crashes. The crash risk factor analysis established a better understanding of the significance of bicycle and pedestrian risk factors. Figure 3 identifies the crash risk factors used to develop this index, the groupings associated with those factors, as well as the significance of each risk factor in relation to bicycle and pedestrian crashes.

Step 4: Establishing Factor Weights To establish the impact of each crash risk factor, weighting was applied based on the proportion of roadway mileage to nonmotorized crashes associated with each crash risk factor category, or the percentage of roadway infrastructure divided by the percentage of historic crash occurrence. This was then normalized and calculated on a scale of 0 to 100. Figure 4 illustrates the crash analysis and weights for each factor, sorted by grouping.

Step 5: Risk Index Scoring To illustrate non-motorized risk at the regional level, a composite score was generated that was comprised of the sum of all crash risk factor weights and scaled between low to high risk. The scaled risk (out of 100) is made up of each risk factor’s weight added together.

The risk factor weights were assigned to the region’s roadway network as illustrated in Figure 6 to identify the risk for nonmotorized crashes in the network. This is not a predictive model, but rather an illustration of areas where there is a disproportionally high or low risk of bicycle and pedestrian crashes occurring.

Figure 4: Risk Index Weighting Difference by Factor

CONCLUSION

Transportation planners have an essential role in building healthy communities, especially at the regional transportation level where federal and state funds are programmed. There is an increased focus on reducing bicycle and pedestrian fatalities and ensuring equitable investment in communities.

A systemic approach to analyze nonmotorized crashes can help transportation agencies and practitioners identify and prioritize high-risk areas for non-motorized safety improvements. This risk index can be useful for transportation agency staff as they update their safety improvement programs, bicycle and pedestrian planning, and prioritize current and future projects. For example, to prioritize funding for bicycle and pedestrian improvements, transportation agencies and local governments can use this index to identify areas where there is high risk for a bicycle and pedestrian crash to occur, ultimately strengthening the argument for improvements in those areas. Moreover, this index provides the ability to quantify planning interventions pre- and post-treatment. Thus, providing further evidence for the successes of proposed programs.

Though this is not a predictive model, the non-motorized risk index can provide a comprehensive look at unsafe areas and where there may be demand for walking and biking when used in-tandem with other non-motorized datasets, such as Latent Demand, which shows where future demand for walking and bicycling is low, medium, and high across the region.

Figure 6: Non-Motorized Risk Index Map for Nashville Region MPO