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Safety Data and Analysis in Developing Emphasis Area Plans (2008)

Chapter: Section III - Details of the Three-Stage Process

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Suggested Citation:"Section III - Details of the Three-Stage Process." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Data and Analysis in Developing Emphasis Area Plans. Washington, DC: The National Academies Press. doi: 10.17226/14170.
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Suggested Citation:"Section III - Details of the Three-Stage Process." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Data and Analysis in Developing Emphasis Area Plans. Washington, DC: The National Academies Press. doi: 10.17226/14170.
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Suggested Citation:"Section III - Details of the Three-Stage Process." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Data and Analysis in Developing Emphasis Area Plans. Washington, DC: The National Academies Press. doi: 10.17226/14170.
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Suggested Citation:"Section III - Details of the Three-Stage Process." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Data and Analysis in Developing Emphasis Area Plans. Washington, DC: The National Academies Press. doi: 10.17226/14170.
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Suggested Citation:"Section III - Details of the Three-Stage Process." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Data and Analysis in Developing Emphasis Area Plans. Washington, DC: The National Academies Press. doi: 10.17226/14170.
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Suggested Citation:"Section III - Details of the Three-Stage Process." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Data and Analysis in Developing Emphasis Area Plans. Washington, DC: The National Academies Press. doi: 10.17226/14170.
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Suggested Citation:"Section III - Details of the Three-Stage Process." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Data and Analysis in Developing Emphasis Area Plans. Washington, DC: The National Academies Press. doi: 10.17226/14170.
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Suggested Citation:"Section III - Details of the Three-Stage Process." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Data and Analysis in Developing Emphasis Area Plans. Washington, DC: The National Academies Press. doi: 10.17226/14170.
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Suggested Citation:"Section III - Details of the Three-Stage Process." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Data and Analysis in Developing Emphasis Area Plans. Washington, DC: The National Academies Press. doi: 10.17226/14170.
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Suggested Citation:"Section III - Details of the Three-Stage Process." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Data and Analysis in Developing Emphasis Area Plans. Washington, DC: The National Academies Press. doi: 10.17226/14170.
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Suggested Citation:"Section III - Details of the Three-Stage Process." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Data and Analysis in Developing Emphasis Area Plans. Washington, DC: The National Academies Press. doi: 10.17226/14170.
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Suggested Citation:"Section III - Details of the Three-Stage Process." National Academies of Sciences, Engineering, and Medicine. 2008. Safety Data and Analysis in Developing Emphasis Area Plans. Washington, DC: The National Academies Press. doi: 10.17226/14170.
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16 This section will further define the three-stage process for developing an emphasis-area plan introduced in Section I. It is again noted that the AASHTO Strategic Highway Safety Plan intends that multiple issues should be addressed and multiple plans developed. Much of the emphasis in this guide is on Stage 3 procedures – choosing treatment strategies and targeting them. This is because procedures for choosing emphasis areas of interest and setting the injury and death- reduction goals are covered in NCHRP Report 501 in detail. However, an overview of all three stages will be presented here. Stage 1 – Define/Choose One or More Issues/Emphasis Areas As noted above, the safety planning team will first need to define or choose an issue (emphasis area) or set of issues that need to be addressed. There is a large array of safety problems that could be treated in any jurisdiction. Thus, at first glance, the possible issues are boundless. However, it should be noted that extensive analytical effort was conducted in the develop- ment of AASHTO’s Strategic Highway Safety Plan to identify 22 critical safety issues/emphasis areas. In addition, extensive efforts have been made to identify the best possible low-cost but effective treatment strategies for use in these 22 areas, thus making the development of a jurisdiction-specific safety program much easier. While not always the case, the same critical problems would most likely exist in any jurisdiction. So “defining” here is usually related to determining which of the 22 identified emphasis areas are most critical in your jurisdiction. The choice of emphasis area(s) is usually done with some type of “problem identification” analysis of crash and other safety-related data. This is a critical part of the safety planning process, but the presentation of detailed procedures for con- ducting such analyses is outside the scope of this guide. Instead, the user is referred to NCHRP Report 501: Integrated Safety Management Process (18), which provides details of more than one type of problem-identification procedure in Section D1.3 of Appendix D. The focus of this guide is on the development of safety improvement plans for each emphasis area once the allocation of funds between emphasis areas has been determined. However, these processes can be performed in iterative fashion. Once the safety improvement plans for individual emphasis areas have been developed, it may be desirable to revisit the allocation of funds between emphasis areas and increase or decrease the funding for specific empha- sis areas as appropriate. As described in detail there, the analyst will generally first perform multiple data runs of perhaps each variable in the crash data (e.g., driver age, crash type) to determine which of the data codes within each variable show high frequencies of crashes. Since some crashes are more severe than others, crash severity as well as frequency should be considered in choosing the emphasis areas. As detailed below in Section III, Stage 3 of this guide, one method of combining both frequency and severity is through weighting each crash in each crash type by an economic cost based on its severity. In- formation on economic cost per crash by severity level for 22 different crash types categorized by speed limit category can be found in Crash Cost Estimates by Maximum Police- Reported Injury Severity Within Selected Crash Geometries (22). The use of crash costs rather than just crash frequency will provide the analyst with overall information on which crash types are most important in his/her jurisdiction. Analysts who do not wish to assign explicit costs to individual crash severity levels can use an alternative cost-effectiveness approach using weights for specific severity levels to generate equivalent property-damage-only crash frequencies. This approach is analogous to using estimates of crash costs by severity level, except in this case the severity-based crash costs are replaced by severity-based weights. Both frequency and severity-based crash costs provide initial information based on most important crash types S E C T I O N I I I Details of the Three-Stage Process

and/or combinations of crash types with other crash-related variables (e.g., crash type by time of day). As further de- scribed in Appendix D of NCHRP Report 501 (18), a more detailed procedure in which categories within a given variable (e.g., crash type) can be shown to be “over-represented” is provided in the CARE (Critical Analysis Reporting Environ- ment) (23). In general, and as described in NCHRP Report 501, the analyst will conduct a series of “drill down” analyses to gain details on which issues/emphasis areas are most important for his/her jurisdiction. Stage 2 – Set a Crash, Injury or Death Reduction Goal for an Emphasis Area The emphasis-area team will then use a series of factors to define a reduction goal for deaths and injuries in each of the emphasis areas chosen. This decision will be based on outputs of the Stage 1 analyses (i.e., the problem-size, total crash cost, over-representation, and related outputs of the problem- identification/drill-down analyses), on some estimate of the possible effects of strategies, and on the budget established for the emphasis area. NCHRP Report 501 (18) defines both an initial process and a revised process for establishing these goals. The initial process will most likely be based on “best judgment” of the factors above. The revised process is much more iterative and analysis-driven where initial goals are modified based on analyses that indicate what is realistic given the nature and size of the problem, the known or assumed countermeasure effectiveness for the final list of chosen countermeasures, and the optimization of the exist- ing budget either within a given emphasis area or across emphasis areas. Stage 3 – Define Treatment Strategies and Target Populations Having now defined the issue/emphasis area to be treated (e.g., run-off-road crashes, crashes involving drinking driv- ers) and having defined the crash/injury reduction1 goal (e.g., a 10 percent reduction in the number of fatal and serious in- jury run-off-road crashes on two-lane rural roads), the next step is to define the treatment strategies to be employed and the target population for each strategy. Note that the terms “treatment strategy,” “treatment,” and “strategy” are used interchangeably in the following text. Here, depending on the emphasis area and strategy being addressed, the term “popu- lation” may refer to humans (e.g., older drivers, pedestrians); vehicles (e.g., large trucks, motorcycles); or roadway sites (i.e., individual roadway features, segments, corridors, intersections, and interchanges). High-level safety planning requires that the limited available safety funds be used in the most effective ways. Funds should not be spent on treatments whose effects are small if those same funds could be used for other treatments that would provide greater benefits. Thus, as a minimum, the goal should be to only implement treat- ments whose benefits exceed their costs, and the ultimate goal should be to implement the treatments with the highest ratio of benefits to costs. However, to base safety planning deci- sions on benefits and costs requires that the effectiveness of each potential treatment be defined (e.g., treatment “X” will reduce run-off-road crashes by 15 percent or treatment “Y” will reduce older driver crashes by 20 percent). However, a review of any of the NCHRP Report 500 guides will indicate that there are many treatments that have been tried – in some cases used very widely – and are gener- ally considered to have a positive effect on safety, but have never been formally evalu- ated in a well-designed study from which an acceptable quantitative level of effectiveness (i.e., a specific CRF or AMF) has been devel- oped. For this reason, the process of choosing treatments and choos- ing targets for each treatment will be cov- ered in four different procedures: • Procedure 1 – for application to road- way-based treat- ments with a known effectiveness level where a complete set of data (e.g., crash, roadway inventory, 17 1 Note that the term crash/injury reduction will be used instead of crash reduction throughout this guide. In most cases, the two terms can be thought of as interchangeable. However, because the ultimate goal of safety programs is to reduce death and injury, and since this can be accomplished both by reducing crash frequency and by reducing the severity of crashes, the former term is considered more appropriate than the latter. In addition, it should be understood that the term “injury” includes both fatal and nonfatal injuries. Thus, the crash/injury reduction from a treatment may represent a reduc- tion in crash frequency, a reduction in crash severity, or both. Crash Reduction Factor vs. Accident Modification Factor The level of effectiveness of a treatment is referred to in much of the current safety literature as a Crash Reduction Factor (CRF) or Accident Modification Factor (AMF). The two terms are just different ways of expressing treatment effectiveness levels. A CRF provides the expected proportional reduction in crash frequency, for all crashes or for specific crash severity levels, so a 15 percent reduction in crashes would correspond to a CRF = 0.15. Likewise, a 20 percent reduction in fatal and serious in- jury crashes would correspond to a CRF = 0.20. An AMF is de- veloped by subtracting the CRF from 1.00, with an AMF of 1.00 representing no effect on safety. Thus, a treatment with a 15 per- cent effectiveness would have an AMF of 0.85 (i.e., 1.00 − 0.15). AMFs above 1.00 indicate that the treatment can be expected to result in an increase in crashes.

intersection inven- tory, traffic counts) are available for planning purposes • Procedure 2 – for ap- plication to roadway- based treatments with known effec- tiveness, but where only crash data, but not inventory or traf- fic volume data, are available (e.g., for local jurisdictions without inventory data) • Procedure 3 – for application to both roadway treatments that do not have specified levels of effectiveness and driver-based treatments with or without known effectiveness • Procedure 4 – a hybrid of Procedures 1, 2, and 3 for consid- ering treatments with known effectiveness and treatments without known effectiveness in the same process Procedures 1 and 2 are based on an economic (benefit- cost) analysis. Procedure 3 is not based on economic analy- sis, while Procedure 4 combines economic and non- economic procedures. The selection and targeting of driver- and vehicle-based treatments is not based on an economic analysis. The following discussion provides an overview of each of these four procedures. Details of each of the procedures will be presented in the individual sections concerning specific treatment types. Procedures 1 and 2 generally result in plans whose expected safety benefits are more accurately known than Pro- cedures 3 and 4, because Procedures 1 and 2 are applicable to treatments whose effectiveness has been well documented. Therefore, the safety planning process should generally exhaust funding opportunities under Procedures 1 and 2 before proceeding to Procedures 3 and 4. Exhibit III-1 will guide the user to the appropriate proce- dure for each analysis situation. The key considerations in choosing one of the four procedures are whether the effective- ness of the treatment(s) is known and whether the available crash data are “mileposted.” In many states, the achievement of a statewide goal for crash reduction will involve consideration of treatments both with and without known effectiveness and consideration of roads under both state and local jurisdiction, which are likely to involve crash datasets that are both mileposted and not mileposted. Thus, many states may need to use more than one of the four procedures. The application of each of these procedures is described below. Procedure 1 – Choosing Roadway-Based Treatments and Target Populations When Treatment Effectiveness Is Known, and Both Crash and Non-Crash Data are Available As indicated above, the highest level of treatment selection/ targeting analysis represented by Procedure 1 is based on an economic analysis procedure. This procedure is applicable to treatments intended to improve safety on roadway segments or at intersections. If required data are available or can be devel- oped, Procedure 1 will provide the user with best selection of treatments and with the most detail on where the treatments should be targeted. It will also provide better assurance to the user in the planning process that the established crash/injury reduction goal can be met. The increase in the precision of the analysis, in comparison to the other procedures discussed below, will result in much better allocation of safety dollars. For these reasons, Procedure 1, where feasible, is strongly recom- mended to the user. Detailed examples of the application of Procedure 1 in which multiple potential treatments and treat- ment targets are examined to produce a final recommended program are presented at two FHWA web sites: http:// safety.fhwa.dot.gov/roadway_dept/docs/lanedeparture/index. htm and http://safety.fhwa.dot.gov/intersections/intersection sap.htm (24,25). Procedure 1 is suitable for roadway-based treatments that address specific crash types and are aimed at modifying road- way segments or intersections. However, it should be noted that Procedure 1 can also be applied to driver- or vehicle- related treatments if the effectiveness of the treatment is known, and if the treatment is to be targeted to specific loca- tions on the highway. Examples include red-light-running enforcement targeted to intersections with high numbers of 18 Why Perform the Higher Level Analysis Shown in Procedure 1? • Selects treatments better • More detail on target road- ways or intersections for each treatment • Provides better assurance that established goals can be met • Provides better allocation of limited safety dollars Inventory Data Available and Linkable to Crashes? Yes No Treatment Effectiveness Known? Mileposted Crashes Mileposted Crashes Unmileposted Crashes Yes Procedure 1 Procedure 2A Procedure 2B No Procedure 3 Procedure 3 Procedure 3 Some known, some unknown Procedure 4 Procedure 4 Procedure 4 Exhibit III-1. Guide to choice of procedures based on knowledge of treatment effectiveness and crash data quality.

such crashes or truck inspection programs targeted to locations or corridors with high numbers of crashes associ- ated with truck speeding or mechanical failure. It should also be noted that, while Procedure 1 is driven by hard data (e.g., information on costs, benefits, crash counts, roadway mileage), there are other policy issues that must also be considered before implementation, including user accept- ability. The FHWA Sample Plans (24, 25) noted above also provide thoughts on such issues. For example, the first plan recommends limiting “the installation of shoulder rumble strips to rural highways where there are no concentrations of homes due to the noise issue,” and conferring “with state or local pedestrian/bicycle coordinator concerning potential application of shoulder rumble strips on bicycle routes.” Since these are policy decisions, each user will need to decide what criteria are necessary. However, the point is that careful consideration of such issues is important. To implement Procedure 1, which provides the highest level analysis of roadway-based treatments, the following data are required: • A specified effectiveness level (Crash Reduction Factor or Accident Modification Factor) for each treatment to be considered • A computerized crash data file which includes sufficient crash details to identify crash types that will be affected by each treatment (“target crashes” such as run-off-road crashes, head-on crashes, run-off-road on curves), and which includes crashes for all potential target populations • Computerized roadway inventory data and/or intersection inventory data that can be linked to the crash data by loca- tion of the crash • A network screening computer program which will exam- ine each segment of roadway of a given length (e.g., 1 mile) or each intersection and calculate the number of target crashes that have occurred on each segment in the past 3 to 5 years (see further discussion below) • Computerized traffic count data that is part of the roadway or intersection inventory data or can be linked to it • Unit cost for each treatment – both original implementa- tion costs and annual maintenance costs If these data are available, Procedure 1 will lead the user through a series of steps that will allow the user to choose a set of treatments and a set of targets (e.g., locations or subpopulations) for each chosen treatment that will both meet the established crash/injury reduction goal, and will be cost-beneficial at some prescribed level. To do this, the user must analyze each potential treatment separately (choosing targets for each) and sum potential crash injury reductions across all treatments to determine if the established goal can be met. If not, new treatments or strategies should be added. While the detailed procedure will be presented in the indi- vidual strategy-based sections, the steps include the following: 1. Specify the types/classes of roadway segments that are potential targets for the treatments. 2. Develop critical crash frequencies for each candidate treat- ment – the frequency of target crashes per mile or per intersection that, if treated, will result in crash/injury reductions whose economic benefit will exceed imple- mentation costs by some specified factor. In the examples provided in the two FHWA Sample Plans (24, 25), the benefit-to-cost ratios used were 2.0 or greater. 3. Using the inventory file, stratify potentially treatable roadway segments by roadway class. 4. Link target crashes with roadway segments or intersections from the appropriate inventory data file, and then perform a computer screening of all potential locations (segments or intersections) to determine which have crash frequen- cies that exceed the critical crash frequencies. 5. If performing a roadway segment analysis, correct the output for “treatment gaps” along the same route result- ing from the network-screening computer program. 6. Estimate the expected crash injury reductions on all the identified target locations. 7. Repeat the above steps for each potential treatment type. 8. Correct for multiple treatments on the same segment. 9. Sum all expected crash injury reductions for all chosen treatment types and chosen target locations and compare that total to the established goal. 10. Add either new treatments or new targets or new approaches (e.g., inclusion of safety treatments in normal maintenance or rehabilitation efforts) until the goal is met. The following flow chart shown in Exhibit III-2 illustrates this procedure. A key advantage of having effectiveness measures for each treatment, as is the case in Procedure 1, is that the full set of treatments needed to reach the crash/injury reduction goal can be determined. The user can also determine the cost of implementing those treatments and, thus, determine the cost of meeting the established crash/injury reduction goal. The cost of meeting the goal should then be compared to the available budget for safety improvement. If the cost of achiev- ing the goal is within the available budget, the required funds should be programmed; depending on the size and nature of the improvement program needed to reach the goal, the pro- gramming of these treatments may be in a single year or over a multi-year period. If the cost of achieving the goal exceeds the available budget, the user can request an increased budget from agency management, which may in turn inform higher political authorities (executive and legislative) of the funding level needed to meet the goal. If the funds required to meet 19

the goal are not available, the user should proceed with the portion of the program that can be implemented and should inform agency management that the program will proceed as far as practical, but that the established goal cannot be met. The reason for using a network screening program is that crashes are not uniformly distributed along a route; the network screening program identifies locations where crashes of particular types are concentrated, which represent poten- tial improvement locations. Many highway agencies have developed computer programs to screen the highway network for high crash fre- quencies and new software tools to perform such screening are under development. Existing highway agency screening programs typically use a “sliding window” approach in which a “window” of specified length is moved forward along the road in steps of specified length and the crash frequency within the “window” is checked at each step. Such existing network screening programs can be used to implement Procedure 1. A window length of 1 mile is recommended for use with existing network screening programs. A more sophisticated network screening approach will be possible with FHWA’s SafetyAnalyst software tools which are currently under development. SafetyAnalyst (see http://www. safetyanalyst.org) uses a new screening approach, known as “peak searching” and a variation of the “sliding window” approach based on improved statistical methods. The “peak searching” algorithm in SafetyAnalyst uses a variable win- dow length based on homogeneous roadway segments. The SafetyAnalyst “sliding window” approach uses window lengths that can be selected by the user; this will allow the use of window lengths shorter than 1 mile and will allow the win- dow length to move forward in steps that are shorter than the window length. Network screening has typically been per- formed by highway agencies in computer database programs, but techniques for performing network screening in a Geo- graphic Information Systems (GIS) environment are being developed. Procedure 2 – Choosing Roadway-Based Treatments and Target Populations When Treatment Effectiveness Is Known and Crash Data Are Available, but Detailed Inventory Data Are Not Available Procedure 2 for roadway-based treatments is intended for application on roadway segments or at intersections in “limited-data” situations. Here, crash data are required, but a formal roadway segment or intersection inventory database is not required. Thus, Procedure 2 is intended for application by highway agencies that do not have detailed computerized in- ventory data on the characteristics of each roadway segment and/or intersection. The goal is the same – to select a set of treatments with target locations identified for each treatment that, if treated, will ultimately allow the user to meet the es- tablished crash/injury reduction goal, and to do so such that the economic benefits of the crash-injury reductions exceed 20 Exhibit III-2. Flow chart illustrating procedure 1.

the treatment implementation costs. The lack of detailed in- ventory data on individual roadway segments or intersections means that estimates concerning treatment effects are not as accurate as in Procedure 1, and that the targets identified are not as likely as those in Procedure 1 to provide the intended re- sults. Thus, the user cannot have as much faith in the benefit- to-cost results as was the case with Procedure 1. Procedure 2 has two variations. In the first, designated below as Procedure 2A, while an inventory database is not required, each crash must be “mileposted” (i.e., given a specific “ad- dress” on a specific route) with sufficient accuracy such that clusters of crashes can be found and the locations at which those clusters occur can be identified as candidate improve- ment locations. This is likely to be the case for many state high- way agencies when intersection treatments are being analyzed, since most highway agencies will have mileposted all crashes but do not have an “intersection inventory” that provides the (mileposted) location of each intersection on each route. This may also be the case for local agencies (e.g., counties, cities, towns) that can provide a “milepost” or other “address” for their crashes. Currently, more highway agencies have de- veloped roadway-segment inventory data files than have de- veloped intersection-inventory data files. Therefore, some highway agencies may find that they can apply Procedure 1 to roadway segment improvements, but that they must apply this first variation of Procedure 2 to intersection improvements. The second variation of Procedure 2, designated below as Procedure 2B, requires crash data that is addressed to a given street or route within the jurisdiction (e.g., a route within a given county), but the crash data does not have to be “mile- posted” to a specific location on that route. The disadvantage of this procedure as compared to either Procedure 1 or the “mileposted-crash version” of Procedure 2A is that only full routes within a jurisdiction (e.g., a county or township) can be analyzed. Thus, a route will not pass the benefit-cost screen unless there are sufficient crashes (and thus potential crash/injury reductions) on the full route to overcome the cost of treating the full route, and the user will not be able to determine which segments of a given route would produce results that have a higher B/C ratio. Since Procedure 1 is likely to provide better and more accurate safety improvement plans than either of the versions of Procedure 2, it is important to the future expansion of highway safety programs that more agencies move toward the development of roadway segment and intersection inventory data files. Since the information on safety improvements pro- vided by Procedure 2B will not be as accurate or as detailed as that for Procedure 2A, it is also important that agencies move toward a system where all crashes are “mileposted.” Procedure 2A – For Mileposted Crashes. To implement the mileposted-crashes version of Procedure 2, designated as Procedure 2A, which applies a “medium level” analysis of roadway-based treatments, the following data are required: • A specified effectiveness level (CRF or AMF) for each treat- ment to be considered • A computerized crash data file which includes sufficient crash details to isolate target crash types (run-off-road, head-on crashes, and run-off-road on curves) and potential target populations that will be affected by each treatment, and which is “mileposted” such that the location of each crash is included • A network screening computer program which can read an input file composed of target crash records sorted by route and milepost, and can count the number of target crashes within a given specified length (e.g., 1 mile for segment- based treatments and 500 ft for intersection treatments) that have occurred in the past 3 to 5 years • Unit cost for each treatment – both original implementa- tion costs and annual maintenance costs If these data are available, Procedure 2A will lead the user through a series of steps that will allow the user to choose a set of treatments and a set of targets for each chosen treatment that will both meet the established crash/injury reduction goal, and will be cost-beneficial at some prescribed level. As with Procedure 1, one must analyze each potential treatment separately (choosing targets for each), implement a procedure which estimates “combined effectiveness” for segments or intersections where multiple treatments for the same crash types will be applied, correct for “treatment gaps” along the same route if a segment-based program, and sum potential crash injury reductions across all treatments to determine if the established goal can be met. If not, new targets or strate- gies should be added. While the detailed procedure will be presented in the indi- vidual strategy-based sections (e.g., see Section IV, “Roadway Segment Programs”), the steps in the process are essentially identical to the steps in Procedure 1, with the exception that the network screening program is used somewhat differently. The steps include the following: 1. Develop critical crash frequencies for each candidate treat- ment – the frequency of target crashes per mile or per inter- section that, if treated, will result in crash/injury reductions whose economic benefit will exceed implementation costs by some specified factor. 2. Sort crashes by route/milepost in ascending order, and then perform a computer screening of all segments on all routes that are potential treatment locations to determine which segments have target crash frequencies that exceed the critical crash frequencies calculated in Step 1. 21

3. If performing a segment-based program, correct the out- put for “treatment gaps” along the same route resulting from the network screening computer program. 4. Estimate the expected crash injury reductions on all the identified target locations. 5. Repeat the above steps for each potential treatment type. 6. Correct for multiple treatments on the same segment or at the same intersection. 7. Sum all expected crash/injury reductions for all chosen treatment types and chosen target locations and compare that total to the established crash/injury reduction goal. 8. Add either new treatments or new targets or new ap- proaches (e.g., inclusion of safety treatments in normal maintenance or rehabilitation efforts) until the crash/ injury reduction goal is met. Procedure 2B – For Unmileposted Crashes. To imple- ment the version of Procedure 2 without mileposted crashes, which applies a “medium level” analysis of roadway-based treatments, the following data are required: • A specified effectiveness level (CRF or AMF) for each treat- ment to be considered. • A computerized crash data file which includes sufficient crash details to identify crash types that will be affected by each treatment (“target crashes” such as unsignalized in- tersection crashes, run-off-road crashes, head-on crashes, and run-off-road on curves), and which includes crashes for all potential target roadways. Each crash record must contain a county or jurisdiction name where the crash oc- curred, and a “route/road on” variable – the name of the route or road where the crash occurred. If intersection treatments are being considered and the crash record con- sistently includes the name of the crossing roadway, then it may be possible to treat the intersection crashes as mile- posted, and Procedure 2A may be used, even though the “mileposts” are not numerical. However, in this situation, it may not be possible to consider intersection-related crashes that occur on the intersection approaches at some distance from the intersection. • “Route length” information that will provide the length in miles of each road or route within a county that is a potential target for any treatment, or at least the approximate length. • Unit cost for each treatment – both original implementa- tion costs and annual maintenance costs. If these data are available, Procedure 2B will lead the user through a series of steps that will allow the user to choose a set of treatments and a set of targets for each chosen treatment that will both meet the established crash/injury reduction goal, and will be cost-beneficial at some prescribed level. As with Procedure 1, one must analyze each potential treatment separately (choosing targets for each), implement a procedure which estimates “combined effectiveness” for segments or intersections where multiple treatments for the same crash types will be applied, and sum potential crash injury reduc- tions across all treatments to determine if the established goal can be met. If not, new targets or strategies should be added. While the detailed procedure will be presented in the indi- vidual strategy-based sections, the steps include the following: 1. Develop critical crash frequencies for a candidate treat- ment – the frequency of target crashes per mile or per intersection that, if treated, will result in crash-injury reductions whose economic benefit will exceed imple- mentation costs by some factor. 2. Link target crashes with each route or intersection in each jurisdiction (but not to a specific point on the route). This will require computer sorting of crashes by each named route or at each named intersection. Some manual effort will be required to correct misspelled names and to group routes or streets that have multiple names. 3. Count target crashes for each route or intersection and enter the total counts into a spreadsheet (one route or intersection per row), along with the route mileage for that route (if using a segment-based program). Repeat this step for each route and/or intersection in the juris- diction under study. 4. Use the spreadsheet to calculate annual crash frequencies for each potential route or intersection. 5. Define possible target routes or intersections by deter- mining which have calculated annual frequencies that exceed the developed critical crash frequencies. 6. Estimate the expected crash injury reductions on all the chosen target locations by adding up target crashes and multiplying by the treatment effectiveness level. 7. Repeat the above steps for each potential treatment type. 8. Correct for multiple treatments on the same route or at the same intersection. 9. Sum all expected crash injury reductions for all chosen treatment types and chosen target locations and compare that total to the established goal. 10. Add either new treatments, new targets or new approaches (e.g., inclusion of safety treatments in normal mainte- nance or rehabilitation efforts) until the goal is met. Procedure 3 – Choosing Driver, Vehicle or Roadway Treatments and Target Populations When Treatment Effectiveness in Terms of Crash/Injury Reduction Is Not Known The two procedures described above allow the user to choose treatments and treatment targets for a given problem while ensuring that the economic value of the crash-injury 22

reductions will exceed the cost of implementing the program. Both procedures require that the treatments being examined each have a known level of effectiveness expressed in terms of an expected crash/injury reduction – a defined CRF or AMF. Unfortunately, many of the roadway-oriented treatments and many of the non-roadway-oriented treatments (i.e., driver- and vehicle-oriented strategies) in the NCHRP Report 500 guide series do not have defined levels of effectiveness. Thus, economic analyses like those that are the basis for Procedures 1 and 2 are not possible for these treatments. Despite the inability to perform formal economic analyses, the user can still make an educated choice of which treat- ments will be most effective in their jurisdiction, and can de- velop a targeting strategy for the treatment in cases where it is not to be applied jurisdiction-wide (e.g., where specific counties, communities, roads, or driver groups are to be tar- geted). In general, the choice of treatment will be based on “what is likely to work best for the target group” and the choice of targets will be based on identification of locations “where the crash/injury problem of interest is found.” From the description of Procedure 3 presented below, it should be apparent to the user that this procedure could produce results that are far less likely to fulfill the established safety goal than the results of Procedures 1 and 2. Nevertheless, when data to use Procedures 1 and 2 are lacking, Procedure 3 is the best available substitute. The obvious drawbacks of Procedure 3 highlight the need for better data systems to implement analysis procedures that are expected to be more accurate. The analysis of treatments without documented crash/ injury reduction effectiveness should focus on those treat- ments for which the user decides that there is some evidence of a crash/injury reduction benefit, even if a documented CRF or AMF based on research using crash data is not available. The NCHRP Report 500 guide series classifies treatments into three types – proven, tried, and experimental – based on whether credible evaluations based on crash data have been performed (i.e., a CRF or AMF has been defined). The proven treatments are those that have been shown through credible evaluations to be effective in reducing crashes. However, not all treatments classified as proven will have a CRF, since some evaluations are based on outcomes that are related to crash/injury reduc- tion but do not actually have a measured and quantified value for the expected reduction in crash/injury frequency. For ex- ample, the effect of occupant restraint laws is stated in terms of “restraint use increase” rather than crash-injury reduction. The treatments classified as tried include those treatments that have been used by agencies (in some cases used often), where there is little possibility of negative impacts on crash/injury frequency, and where there is an expectation (but not scien- tific proof) that the effect of the treatment on safety is likely to be a positive one. The evidence could include poorly designed or executed crash/injury evaluations and indirect or surrogate measures that may be related to safety (e.g., behavioral changes that may be related to crash/injury reduction). The treatments classified as experimental are treatments that have the potential to be beneficial, but have had only limited use and cannot be considered either proven or extensively tried. As stated in each of the NCHRP Report 500 guides, these experimental treatments should be used with care, only in pilot programs, and should be evaluated carefully before wide- spread implementation. The Sample Plans presented at the FHWA web sites (24, 25) include example plans for such pilot programs. Thus, the process described below is intended for application only to proven and tried treatments. Procedure 3 is intended for application to tried or experi- mental treatments for which the analyst has decided that there is likely to be a crash/injury reduction benefit, but for which the analyst does not have sufficient evidence to estimate a spe- cific CRF or AMF value. In the event that the analyst is able to estimate a specific CRF or AMF value, even if the estimate is only an approximation, it is recommended that Procedure 4 be used rather than Procedure 3. Unlike Procedures 1 and 2, when crash/injury reduction effectiveness of a treatment is not known, guidance on how to choose among several potential treatments and how to tar- get the treatments selected is much more general in nature, and will require “best judgment” on the part of the user. The following general approach to Procedure 3 is suggested for a single issue or emphasis area (e.g., head-on crashes on two- lane roads or older driver crashes), but can be repeated for multiple emphasis areas. Procedure 3 should be applied in two steps. First, choose the “best treatments” (i.e., the treatments most likely to be applicable in a given jurisdiction) from among the set of all treatments presented in the NCHRP Report 500 guide appli- cable to the emphasis area in question. Second, choose the target locations or populations to which the selected treat- ments should be applied. The choice of the “best treatments” from a listing of many potential treatments can be based on the following factors: a. Which of the many potential treatments is judged to be the most effective? Even though the exact crash/injury reduc- tion effects of each potential treatment are not known, there may be some knowledge of which treatments are more likely to be the most effective. To develop an imple- mentation plan in the absence of treatment effectiveness estimates, the user must exercise judgment about which treatments are best suited to a particular problem. The detailed information in the NCHRP Report 500 guide series, particularly in the section of each strategy discussion labeled “Expected Effectiveness,” will provide the user with a summary of current knowledge on which judgment can be based. The knowledge in the NCHRP Report 500 guides 23

may be supplemented with the past experience of the agency with the treatments under consideration. There are also some general approaches that can be based on past examinations of different strategy types over time. For example, for programs aimed at drivers and vehicles, treatments that incorporate legal sanctions will usually be more effective than education, and education linked with enforcement will usually be more effective than either alone. For roadway-based treatments, the best of multiple choices without known effectiveness will often be the treat- ment that can potentially affect the crash types and sever- ity levels that are most prevalent at the locations or on the portions of the roadway system under consideration for treatment (see factor “b” below). b. The relative magnitude of the crash types and severity levels that the treatment will affect. In general, the user should focus on treatments that could affect the largest portion of the ex- isting crash experience at the locations or on the portion of the roadway system under consideration for treatment. The use of a “drill down” approach to crash data analysis to determine as many specifics of crash type and severity dis- tributions related to the issue under study is recommended. Thus, if one is attempting to reduce older driver crashes, then a preliminary analysis should be performed using available crash data to determine the frequencies and pro- portions of different types of crashes involving older drivers. Then, treatments that target the most prevalent crash types should be selected. Problem analysis of this type is an iterative process; the results of one analysis of crash data may suggest another. A sequence of analyses may eventually lead to the identification of a treatment or a set of treatments that appear to address the most prevalent crash types. It cannot be ensured that the treatments that address the most preva- lent crash types will, in fact, produce the largest crash reductions, but in the absence of treatment effectiveness estimates, a focus on treatments that address the most prevalent crash types is a logical choice. c. The cost of the potential treatments per target unit (either per person or per mile or per intersection). d. Other technical or policy considerations – there may be reasons you can’t implement a potential strategy in your jurisdiction, even if it’s potentially the “best” (e.g., some jurisdictions may not allow the removal of roadside trees, or some treatments require enabling legislation such that municipalities cannot use the treatment without authorization under state law). These factors must be combined in some fashion to first decide which treatment to choose. While there are multiple ways of making this choice, the following represents one such procedure. 1. Prioritize the specific crash types (within your chosen emphasis area) to be addressed. This is related to Factor b in the above list. Here, for the roadway-departure area, the issue is whether to treat run-off-road, head-on, tree-related or other roadway segment crash types, and on which roadway systems (e.g., two-lane rural roads, four-lane divided roads, free- ways). For driver-related programs, the issue might be whether to treat younger or older drivers, or even which crash types affecting older drivers to target. Whatever the issue, the prioritization will be based on the frequency and severity of the specific types of target crashes occur- ring in a user’s jurisdiction. For each crash type, the user could begin the process by analyzing 3 to 5 years of crash data to determine the frequency of each type. However, since some crash types are more severe than others (e.g., head-on crashes are more severe than run-off-road crashes), total crash frequency alone does not provide the complete answer. While an alternative is to restrict the analysis to only fatal and serious-injury crashes, this will severely limit the crash sample, and will also omit a large component of the crash problem – non-serious in- jury and no-injury crashes. A better solution is to weight each crash by an economic cost based on its type and severity, and then accumulate the total crash cost within each target crash type. Information on economic cost per severity level within 22 different crash types can be found in Crash Cost Estimates by Maximum Police-Reported In- jury Severity Within Selected Crash Geometries (22). This analysis of crash costs will provide the user with overall information on which lane-departure crash type has the greatest economic impact. It is noted that the 22 crash types covered in this FHWA report are types defined by what is hit (vehicle-pedestrian, vehicle-vehicle, vehicle-object, vehicle rollover) and the nature of the impact (angle, rear-end, head-on, etc.); the type of crash location (intersection or non-intersection); and two speed limit groups (≤ 45 mph or ≥ 50 mph). The types do not include crashes for specific vehicle types (e.g., truck and motorcycle crashes), specific driver populations (older vs. younger drivers), or for certain crash situations (e.g., crashes in work zones). However, since the eco- nomic costs are derived for each level of crash severity, the user can develop a weighted per-crash cost for any crash scenario (e.g., work zone crashes, truck-car crashes, older driver crashes) by using the severity distribution of that crash scenario in their own data sample. The user may further refine this analysis by examining crash frequency or total crash cost within roadway classes. If the crash data are mileposted and linkable inventory data are available, details of roadway types can be linked to each crash record (e.g., number of lanes by divided/undivided). If inventory data are not available, there may be variables on the crash record itself that can be used in a less-detailed analysis (e.g., number of lanes, rural vs. urban, route type). 24

This analysis will then produce a listing of potentially treatable crash types (perhaps by road class) that can be sorted by crash frequency or total crash cost, thus providing a ranked listing. For the higher-ranked crash types, the user can then conduct additional analyses to determine more of the specifics of the crash circum- stances (e.g., nighttime vs. daytime distributions of total crash costs). These additional “drill-down” analyses should be designed to provide additional information that could lead to the choice of one treatment over another (e.g., raised pavement markers are primarily effective at night or in rainy weather). 2. Identify possible treatments for use for each high- priority crash type. The user will then review the pertinent NCHRP Report 500 guides and list treatments that would be most appropriate for each of the high-priority crash types iden- tified in the above step. The choice should be limited to those treatment strategies that are classified as tried in the guides. (Proven treatments have known effectiveness lev- els and can be analyzed in one of the three procedures above.) If not already conducted in the “drill-down” analysis in the preceding step, more specific information on the crash costs related to each potential treatment strat- egy could be developed by specifying the crash types that are most likely to be affected by each strategy (e.g., night- time run-off-road-right crashes for raised pavement markers), producing crash frequencies for each specified crash type, and multiplying the frequencies by cost per crash. For some strategies, the NCHRP Report 500 guide presents information concerning which crash types are most likely affected by that treatment strategy. 3. Rate the possible treatments based on estimated effectiveness. Since this procedure deals with treatment strategies with unknown effectiveness, this appears to be impossible. How- ever, for a given set of possible treatments for a particular crash type/road class combination, it may be feasible to make a judgment concerning which treatment strategy would be expected to be most effective. For example, for run-off-road crashes on two-lane rural roads, one would as- sume that rumble strips on two-lane rural roads would be more effective than wider edge lines or raised delineators. For alcohol-related crashes or occupant-restraint-related crashes, treatments involving enforcement coupled with public information are more effective than either approach by itself. At times, this will clearly be a very difficult judg- ment to make. 4. Choose “best” treatment(s) by considering estimated effectiveness, unit cost and other technical and policy considerations. The user will then combine the output of the steps above with at least two other factors in making a final decision on which treatment(s) to implement – the cost per mile of the treatment and other technical and policy considerations. Unfortunately, there are no good guidelines for how to “weight” the different factors. While problem size (total crash cost) and assumed treatment effectiveness are key fac- tors, there may be technical, policy, and cost considerations that will remove certain treatments from consideration even if they are felt to be effective. The user will have to choose the final treatments based on best judgment. The procedure outlined above will at least ensure that the major factors in the decision are clearly defined. The output of this step will be one or more chosen treatments, with the nature of the treatment defining the specific crash types more likely to be affected (e.g., raised delineators will affect run-off-road crashes at night). The user should be able to work backwards using the number of crashes likely to be affected by a given treat- ment and the cost of applying that treatment to a given population or location (see items b and c described at the beginning of this procedure) to determine the treatment effectiveness needed to maintain a cost-benefit ratio greater than or equal to one. Where: • B = economic benefit of applying a selected treat- ment to a given location or population • Ct = the cost of applying that treatment to the selected location or population B = N*Cc*Eff Where: • N = Number of target crashes for the subpopula- tion or location where the treatment is to be applied • Cc = average economic cost per target crash • Eff = treatment effectiveness, or the percent reduc- tion in target crashes Since different severity levels have different crash costs, the value used for Cc can be a weighted average of the crash costs associated with the crash types likely to be affected. Solving for the treatment effectiveness, the equation reads: The analyst can then determine whether the calculated treatment effectiveness required to reach the breakeven point is likely to be achievable. 5. Target the chosen treatments to the roadway segments or subpopulations where the problem is found. Since this procedure concerns treatment strategies with- out known effectiveness, it will not be possible to target the Eff C N C t c = * B Ct ≥1 0. 25

treatments based on any type of economic analysis such as those in Procedures 1, 2A and 2B. Instead, the treatment will be targeted to roadway segments, intersections, or vehicle or driver subpopulations showing the highest total crash cost or frequency, coupled with user judgment con- cerning other characteristics of the potential target groups (e.g., the nature of the roadway and roadside at potential target locations, driver subpopulations most likely to be reached by the treatment), and technical and political issues. More guidance on targeting using Procedure 3 is included in the individual sections that follow. 6. Decide what to do with multiple treatments on the same segments/routes or subpopulations. The above steps could possibly produce roadway loca- tions, intersections, and vehicle or driver subpopulations within a jurisdiction that could be treated with multiple treatments. Unlike the earlier procedures where it is possi- ble to estimate combined effectiveness for multiple treat- ments on the same segments or routes, since treatment ef- fectiveness is not known here, the user will have to use other factors in the final treatment choice for these locations. Again, more guidance is given in the sections that follow. 7. Add new treatments, new targets or new approaches (e.g., inclusion of safety treatments in normal mainte- nance or rehabilitation efforts) until the available funding is used. In Procedures 1, 2A, and 2B, an iterative process is used until sufficient treatment types and locations are selected such that the established crash reduction goal can be reached. In Procedure 3, without effectiveness measures for the treatments, it is not possible to verify whether or not a specific set of treatment types and treatments will meet the established goal. Therefore, the best that can be done is to proceed in selecting treatment types and treatments until the available budget for safety improvement has been fully com- mitted. The total benefit of the selected program will not be forecastable, but the success of the program can be deter- mined by evaluations conducted after its implementation. Procedure 4 – Choosing Treatments and Target Populations in Emphasis Areas for which Some Candidate Treatments Have Known Effectiveness Estimates and Other Treatments Do Not In many situations, users considering a safety improvement program in a particular emphasis area will need to consider both treatments that have known effectiveness measures and treatments that do not. In this situation, it is recommended that the user give priority to treatments that have known effectiveness measures (proven treatments). Treatments that have been used extensively but for which effectiveness measures are not available (tried treatments) should then be considered. Experimental treatments may have a modest role in a safety improvement program, particularly if the program is structured to evaluate the effectiveness of the experimental procedure. The recommended planning approach in this situation is a hybrid of Procedures 1, 2, and 3 described above and includes the following steps described below: 1. Determine if proven treatments can meet the established goal. Consider treatments with known effectiveness meas- ures using either Procedure 1, 2A, or 2B, as appropriate, depending on the types of data available. Determine the crash/injury reduction achieved and compare it to the established crash/injury reduction goal. If the goal has not yet been met, proceed to Step 2. 2. Consider tried treatments to supplement the proven ones. Consider treatments without known effectiveness measures that have been used extensively by highway or driver/ vehicle agencies. If effectiveness measures for these treat- ments can be estimated based on imperfect information, then proceed to Step 3; otherwise, proceed to Step 4. 3. Estimate the effectiveness of tried treatments if possible, and analyze them using the appropriate procedure above. This step involves attempting to estimate the effectiveness of treatments without known CRFs or AMFs. Note that estimating treatment effectiveness is very difficult and can lead to poor treatment choices unless the estimates are realistic. This estimation was not suggested in Proce- dure 3 for this reason. It is only suggested at this point since the user has already considered all proven treatments before reaching this stage. It is suggested that the follow- ing guidelines be used in making such estimates: a) In general, be as conservative as possible. Very few treatments can be expected to affect crash frequency by more than 15 to 25 percent. b) When possible, formulate an effectiveness estimate that is applicable to particular target crash types only, not to total crashes. c) Base estimates for tried treatments on CRFs for similar treatments if they exist. For example, a CRF exists for shoulder rumble strips. Other treatments that also try to keep the driver from leaving the roadway by alerting him (e.g., enhanced edgeline marking, raised profile mark- ing) but do not give the same level of warning would be expected to have somewhat similar, but lower, CRFs. Once effectiveness is estimated, apply Procedure 1, 2A, or 2B as appropriate, depending on the types of data available. Determine the crash/injury reduction achieved in Steps 1 and 3 combined and compare it to the established crash/ injury reduction goal. If the goal has not yet been met, proceed to Step 4. 26

4. Consider additional tried treatments. For treatments for which reliable effectiveness measures cannot be estimated, apply Procedure 3 to select additional treatment types and target locations or subpopulations, until all available funds have been budgeted. Other Safety Analysis Tools The procedures presented above supply a goal-oriented approach to developing plans for safety improvement programs. Users should be aware of other analytical tools that are being developed to assist in this process. FHWA’s Safety- Analyst software, planned for release in 2006 or beyond, is intended for application to safety management of a highway system, but may be an effective tool for safety planning as well. Key capabilities of SafetyAnalyst include: • Screening a highway network to identify sites with poten- tial for safety improvement. • Diagnosing selected locations to identify collision patterns. • Selecting of countermeasures potentially applicable to the identified collision patterns. • Using economic analysis tools to perform cost-effectiveness and benefit-cost analyses. These economic analysis tools will include an optimization routine to select a mix of improvement locations and countermeasures that maxi- mizes the total safety benefits from a given budget for safety improvement. • Priority ranking potential safety improvements based on economic analysis results. • Evaluating the effectiveness of countermeasures after they are implemented. SafetyAnalyst is location-oriented and budget-oriented, un- like the procedures presented above which are goal-oriented. More information is available at www.safetyanalyst.org. FHWA’s Interactive Highway Safety Design Model (IHSDM) may assist in the design and analysis of candidate safety improvements on rural two-lane highways. IHSDM will likely be expanded in the future to address facility types in addition to rural two-lane highways. The forthcoming Highway Safety Manual (HSM), sched- uled for publication in 2008, will present formal procedures for estimating the crash/injury reduction effectiveness of specific improvement types, including an expanded set of CRFs and AMFs representing countermeasure effectiveness. In the meantime, an expanded set of AMFs developed in NCHRP Project 17-25 has been presented in NCHRP Research Results Digest 299 (27). Summary The procedures presented above have defined the overall process for planning safety improvements in any specific emphasis area. At this point, it is assumed that the user will have completed Stage 1 (i.e., define/choose the issue to be addressed) and Stage 2 (i.e., setting a stretch goal) using the guidance provided earlier and guidance provided in other documents such as NCHRP Report 501. The following sections of this manual will provide more detail on how to conduct the final step – treatment selection and targeting – for each of the 22 emphasis areas in the AASHTO Strategic Highway Safety Plan, or for groups of emphasis areas for which the data needed and the procedures to be applied are similar. Subsequent sections provide guidance on how to proceed with the planning process when relatively complete data are available, and when only limited data are available. It is again noted that a jurisdiction’s full safety plan should include multiple issues/emphasis areas (e.g., run-off-road crashes, crashes involving heavy trucks, and crashes involv- ing drinking and driving). Stage 1 will have defined the full set of issues/areas to be addressed, and Stage 2 will have defined goals for each issue. The user can then use the information provided in each of the individual sections below to conduct Stage 3 – treatment choice and targeting – for each of the issues in the full plan. 27

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TRB's National Cooperative Highway Research Program (NCHRP) Report 500, Vol. 21: Guidance for Implementation of the AASHTO Strategic Highway Safety Plan: Safety Data and Analysis in Developing Emphasis Area Plans provides guidance on data sources and analysis techniques that may be employed to assist agencies in allocating safety funds.

In 1998, the American Association of State Highway and Transportation Officials (AASHTO) approved its Strategic Highway Safety Plan, which was developed by the AASHTO Standing Committee for Highway Traffic Safety with the assistance of the Federal Highway Administration, the National Highway Traffic Safety Administration, and the Transportation Research Board Committee on Transportation Safety Management. The plan includes strategies in 22 key emphasis areas that affect highway safety. The plan's goal is to reduce the annual number of highway deaths by 5,000 to 7,000. Each of the 22 emphasis areas includes strategies and an outline of what is needed to implement each strategy.

Over the next few years the National Cooperative Highway Research Program (NCHRP) will be developing a series of guides, several of which are already available, to assist state and local agencies in reducing injuries and fatalities in targeted areas. The guides correspond to the emphasis areas outlined in the AASHTO Strategic Highway Safety Plan. Each guide includes a brief introduction, a general description of the problem, the strategies/countermeasures to address the problem, and a model implementation process.

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