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66 Background and Motivation In addition to analyzing high crash locations, the Arizona Department of Transportation (Arizona DOT) developed a crash risk assessment methodology to proactively identify state highway segments and intersections where investment can help to cost-effectively lower the risk of pedestrian crashes. This methodology considered roadway, environmental, and other risk factors that were frequently identified as contributing factors to pedestrian crashes on their state highway system. Step 1: Define Study Scope Arizonaâs overall strategic pedestrian safety action plan aimed to reduce the greatest number of severe injury and fatal pedestrianâmotor vehicle crashes on the Arizona State Highway System. The systemic program was one part of that overall plan. The state undertook to iden- tify both high crash and high risk locations that may not have experienced crashes. Step 2: Compile Data Arizonaâs process relied on existing data sources that have been spatially linked. See the table in Step 3 for a list of data sources for each risk factor used. Arizona DOT also crash-typed all pedestrian crashes on the state highway system using the FHWAâs PBCAT software. These data C H A P T E R 1 1 Case Example 3: Arizona Department of Transportation Key Takeaways â¢ Used a set of risk factors established by prior research and applied some weighting criteria to these to produce a high risk score. â¢ Used existing GIS-based roadway data along with state roadway files to score and map roadway segments and intersections. â¢ Performed additional visual scan of high-scoring sites to refine potential treatment sites (using on-line street viewing resources) and select candidate countermeasures. â¢ Developed groupings of similar high-crash and high risk sites with similar recommended countermeasures, which allowed for computing benefitâcost ratios of high risk and high-crash sites.
Case Example 3: Arizona Department of Transportation 67 were not used in the initial risk assessment but were available for diagnosing potential conflicts at sites that had prior crashes. Step 3: Determine Risk Factors Arizona DOT used risk factors established from prior research in their approach, divided into three categories: â¢ Existing conditions: factors relating to the lack of pedestrian accommodations; â¢ Pedestrian demand: factors estimating pedestrian exposure; and â¢ At-risk groups: factors in the degree of safety concern that the absence of facilities creates. Table 21 lists the risk factors used by Arizona DOT to help identify locations with high crash risk for pedestrian crashes and their respective data sources. As with the Oregon DOT example, Arizona DOT created a method for developing a risk score for each state highway roadway segment, based on the risk factors shown in Table 21, and weighted values for the presence (or lack) of these factors. The point system was developed sub- jectively and incorporated research results from the latest pedestrian safety literature. For ease of ranking and scoring, Arizona DOT converted the continuous variables into categorical variables. For example, the width of roadway and posted travel speed variables are broken down as follows: â¢ Width of Roadway 6-Lane highway = 6 points 4- or 5-Lane undivided highway = 3 points 2- or 3-Lane undivided highway = 2 points 2- or 3-Lane divided highway = 1 point â¢ Posted Travel Speed > 45 mph = 6 points 35 to 45 mph = 4 points 25 to 35 mph = 2 points < 25 mph = 0 points Risk Factor Category Risk Factor Data Source Existing conditions Posted speed limit Arizona DOT Highway GIS Operating environment/number of lanes/roadway width Missing sidewalk link Paved shoulder width Prior crashes Traffic volume Signalized intersection spacing Pedestrian demand Population density Census Bureau Attractors (e.g., convenience stores, schools, parks) Land use maps and visual inspection (corridor-level only) Land use (commercial and high density housing) At-risk groups % Households in poverty Census Bureau % Households with no vehicle Land use maps and visual inspection (corridor-level only) At-risk groups (children, elderly, and handicapped) Table 21. Pedestrian crash risk factors and corresponding data sources.
68 Systemic Pedestrian Safety Analysis Step 4: Identify Potential Treatment Sites Arizona DOT uses the GIS-based risk scoring tool to identify potential treatment locations on the state highway system. Roadway segments are ranked by the total number of points earned, and high risk locationsâthat is, those with more than 32 total points based on all category variables some of which are not included in Table 21âare mapped using GIS (see Figure 8). These locations were further evaluated visually using Google Earth or other resources to make assessments based on the segmentâs areawide elements such as sidewalk connectivity, signalized intersection spacing, and presence of pedestrian attractors. This step either maintained the seg- mentâs status as being high risk or screened out the location if there seemed little potential for pedestrian activity. Then sites were grouped with others that shared high risk features and where the same countermeasures were proposed. This allowed for computing of a benefitâcost ratio Figure 8. Arizona DOT process to identify high risk segments for potential treatment (Kimley-Horn et al. 2017). Arizona DOT Highway GIS Dataa Sidewalk Connectivity (see criteria) Available Crossing Opportunities (see criteria) Final Risk Assessment Score1/4 Mile from Pedestrian Attractorc Yes No +0 +6 Step 1 - Initial Screening Step 2 - Final Screeningb Geo-Processing: Spatially Combine Layers Identify Initial High Risk Segments aOperating Environment Posted Speed Limit Shoulder Width Existing Crashes AADT Environment Type (Urban/Rural) Population Density Households in Poverty cAdjacent to the following: Convenience/Liquor Store School and Other Educational Facilities Transit Stops Parks bSite visit, Aerials, or Google Earth and Streetview Initial Scoring of State Highway System Segments (sum of each risk variable)
Case Example 3: Arizona Department of Transportation 69 for each of these site groupings, so that the benefits of treatments could be measured across sites with similar risk factors but different crash histories. Step 5: Select Potential Countermeasures Arizona DOT identified a set of effective pedestrian countermeasures and select other counter- measures that may help to address pedestrian crash types along the state highway system from research. Since the state developed both the high crash and high risk plan simultaneously, both high cost measures and lower-to-moderate cost measures were included. Chapter 5 from Arizona DOTâs Pedestrian Safety Action Plan (Kimley-Horn et al. 2017) describes the process and countermeasures selected. Some of the most common recommended countermeasures included the following: â¢ Improving shoulders (e.g., shoulder widening and paving) â¢ Installing lighting where nighttime pedestrian crashes were a problem â¢ Establishing a pedestrian crossing, usually to include high visibility crosswalks, PHBs, and advanced stop lines with pavement markings â¢ Installing raised median islands â¢ Providing signalized crossing improvements, such as leading pedestrian intervals and/or extending the walk interval â¢ Adding pedestrian warning signs at some rural, high crash areas â¢ Developing police enforcement plans for many of the sites In addition, recommendations were made to conduct road safety audits at many of the locations to finalize treatment selection. Step 6: Refine and Implement Treatment Plan For the high crash and high risk locations that were identified from the analysis, candidate countermeasures were assigned a benefitâcost ratio in a similar process recommended in the HSM (AASHTO 2010). Since many of the high risk locations had few or no pedestrian crashes during the analysis period, a procedure was developed to allow for them to also be included in the economic analysis. To accomplish this, sites that were similar in terms of risk factors and with identical countermeasure recommendations were grouped together. Thus, similar high crash and high risk sites were combined. This allowed for the use of the total combined pedes- trian crash number for the group and the crash modification factor for the treatment type in computing the expected crash benefit. The combined cost of the countermeasures at all treat- ment sites in the group was the basis of the cost value in the benefitâcost calculation. Other Steps and Lessons Learned to Date This risk assessment methodology has allowed Arizona DOT to identify segments or corri- dors that have high crash experience and sites that may not necessarily appear on a high crash location list but possess the conditions to be high risk for crashes in the future. By proactively implementing the appropriate countermeasures (after completing a benefitâcost analysis and ranking the results) at the locations identified through this methodology, Arizona DOT aims to help mitigate their high crash risk and potentially prevent the locations from appearing on a list of high frequency crash sites. Arizona DOT applied a benefitâcost analysis to high crash and high risk sites. Due to vari- ability in potential injury outcomes for each crash based on individual crash factors (e.g., age and health of the pedestrian who was struck), the state applied crash costs based on the average
70 Systemic Pedestrian Safety Analysis severity outcome by crash type for all of the prior crashes on the state highway system. Their report also describes how they assigned a service life and annual operating costs, as well as initial construction costs, to each potential countermeasure to be used in the benefitâcost calculations. With less data on pedestrian environments and exposure available for the initial screen- ing process, more work was needed following initial identification of sites with risk factors to identify locations to potentially remove from the pool of sites if they lacked pedestrian demand characteristics. Arizona DOT assisted with information for this case example. The full Arizona Pedestrian Safety Action Plan final report (Kimley-Horn et al. 2017) can be found at www.azbikeped.org/ downloads/ADOT-Pedestrian-Safety-Action-Plan.pdf.