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

Chapter: Section IV - Roadway Segment Programs

« Previous: Section III - Details of the Three-Stage Process
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Suggested Citation:"Section IV - Roadway Segment Programs." 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 IV - Roadway Segment Programs." 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 IV - Roadway Segment Programs." 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 IV - Roadway Segment Programs." 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 IV - Roadway Segment Programs." 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 IV - Roadway Segment Programs." 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 IV - Roadway Segment Programs." 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 IV - Roadway Segment Programs." 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 IV - Roadway Segment Programs." 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 IV - Roadway Segment Programs." 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 IV - Roadway Segment Programs." 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 IV - Roadway Segment Programs." 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 IV - Roadway Segment Programs." 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 IV - Roadway Segment Programs." 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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28 Planning Programs Related to Reducing Crash Types Including Run-Off-Road, Head-On (Including Head-Ons on Freeways), Curve, Utility Pole, and Tree-Related Crashes This section of the guide provides the details of the four levels of treatment choice and targeting procedures described previously in the Stage 3 discussion in Section III, but oriented to those issues/emphasis areas that are specifically related to roadway segments – run-off-road crashes (including those involving utility poles and trees), head-on crashes, and curve- related crashes. This group of crashes is sometimes referred to as “lane departure” crashes. In most instances, a given proce- dure will follow the same basic steps, regardless of the crash type being addressed. Where the procedure differs between crash types, this will be noted. In addition, the data needed for the different roadway-segment-oriented crash types will differ and will be specified. The user is strongly urged to carefully review the material in each of the pertinent guides before beginning this planning process. These roadway-segment- oriented guides are found within NCHRP Report 500: Guid- ance for Implementation of the AASHTO Strategic Highway Safety Plan. The specific volumes pertinent to this section are: • Volume 3: A Guide for Addressing Collisions with Trees in Hazardous Locations (3) • Volume 4: A Guide for Addressing Head-On Collisions (4) • Volume 6: A Guide for Addressing Run-Off-Road Collisions (6) • Volume 7: A Guide for Reducing Collisions on Horizontal Curves (7) • Volume 8: A Guide for Reducing Collisions Involving Utility Poles (8) • Volume 20: A Guide for Reducing Head-On Crashes on Free- ways (26). A link to these downloadable guides can be found at http:// safety.transportation.org/guides.aspx. Possible Program Types – Spot versus System Programs Before moving to the specific treatment choice/targeting procedures for these emphasis areas, it is noted that states who were early participants in the AASHTO safety planning process for roadway-segment (and intersection) programs started from two different perspectives, and the perspective chosen determines the choice and targeting of treatments. Some states chose to try to expand their current “high-crash location” (HCL) program to include more locations to meet their overall goal. Others chose to orient their planning meth- ods to the identification and treatment of “systems” of road- ways, not just those locations that fell under the HCL pro- gram. Indeed, guidance provided in each of the guides, in companion training courses, and in the draft implementation plan on the FHWA website is that system-based programs will need to be included. If the jurisdiction is really attempt- ing to reach a goal which represents a significant change from the current situation – a stretch goal – it is very unlikely that expansion of the HCL program will suffice. While such an expansion is clearly a component of a stretch-goal plan, large- scale treatment of systems and corridors will also likely be necessary. Indeed, a jurisdiction can use the following procedure to de- termine approximately how much the existing HCL program will have to be expanded, which will provide some guidance on whether system programs should also be considered. 1. Examine the most recent listing of HCL projects that were chosen for treatment in your jurisdiction and identify those that were related to lane-departure crashes. (Note that the same procedure could be used for intersection crashes). S E C T I O N I V Roadway Segment Programs

2. Add the numbers of before-treatment crashes, injuries and fatalities from each lane- departure site and divide by the number of years of before data to produce a total num- ber of “potentially treatable lane-departure crashes and crash injuries per year.” 3. Multiply these totals by 20 percent to get the number of lane-departure crashes, injuries and fatalities that are expected to be reduced per year by your current program. (This assumes an average Crash Reduction Factor of 20 percent for all lane-departure strategies. This is probably too high, but in the ballpark of reality, and good enough for this exercise.) 4. Compare the numbers of crashes and injuries reduced and lives saved to your statewide lane-departure goal and calculate the proportion of your total goal that this represents (e.g., 20 percent or 0.20). 5. To calculate approximately how much you will have to expand the lane-departure part of your HCL program to meet your goal, divide 1.0 by the proportion from the pre- vious step. For example, if the fatality and injury savings from your current program is 20 percent of your goal, then you will have to identify and treat five times as many lane-departure sites in the future (i.e., 1.0 / 0.20 = 5). The user will then need to make the determination of whether enough sites with high numbers of lane-departure crashes can be identified. Usually the HCL program identifies more sites than can be treated. This full “census” of potential HCL sites can be examined to determine whether enough sites with high numbers of lane-departure crashes are avail- able. In most cases, if a stretch goal has been set, the answer will be “no.” In that case, the user should consider adding sys- tem improvements to the plan. While all states and some local jurisdictions have proce- dures in place to identify and treat high-crash locations, it is noted that an improved methodology is currently being devel- oped by FHWA in the SafetyAnalyst program described in the preceding Section (also see http://www.safetyanalyst.org). This set of the software tools for safety management of specific highway sites includes a series of procedures that will allow the user to identify high-crash locations or sites with potential for safety improvement, diagnose potential treatment sites to identify correctable crash patterns, conduct an economic analysis to ensure a minimum B/C ratio, and develop a com- bined treatment program which maximizes the benefits that can be gained from a given total treatment budget. The network-screening tools within SafetyAnalyst provide a good approach for applying Procedure 1. The primary emphasis of this guide is on planning site- specific projects at high-crash locations. If preliminary analy- sis indicates that even an enhanced and expanded high-crash location program will not meet the goal, then the users will need to add systems-based or systemwide treatment programs to the effort. This guide is not specifically intended for planning such systemwide treatments, but the four procedures described earlier and detailed below can be ap- plied by the user to identify roadway systems or corridors (or even large numbers of individual segments) to treat and to help define the treatments that should be implemented for those systems or corridors. Again, the choice between which procedure is appropriate is defined by three factors – whether or not treatment effectiveness is known, whether the jurisdic- tion has inventory data that can be linked to their crash data, and whether the crashes are “mileposted” or not. Exhibit IV- 1 will guide the user to the appropriate procedure. Procedure 1 – Choosing Roadway-Based Treatments and Target Populations When Treatment Effectiveness Is Known, and Both Crash and Non-Crash Data Are Available The following text identifies the data needed for conducting Procedure 1, followed by the individual steps in the procedure. Data Needs The following are the specific data needed to use Proce- dure 1 when choosing and targeting roadway-based treatments. • A specified effectiveness level (CRF or AMF) for each treatment to be examined. The “Treatment Effectiveness” section under each treat- ment in each NCHRP Report 500 series guide provides a 29 Exhibit IV-1. Guide to choice of procedures based on knowledge of treatment effectiveness and crash data quality. 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

description of what is known about CRFs. It is important that the user review the material in the guides for a given treatment. Valuable information about the stability of the CRF, cautions about the use of the treatment and other valuable information is included there, but will not be repeated here. For a significant proportion of the treatment strategies defined in the six guides covered in this section, a specific AMF is not presented. Since the preparation of some of the earlier guides, additional information on treatment CRFs has been developed in both NCHRP 17-25, and in prelim- inary work for the Highway Safety Manual. The AMFs from NCHRP Project 17-25 have been published in NCHRP Research Results Digest 299 (27). The AMFs devel- oped in NCHRP Project 17-27 will be incorporated in the forthcoming Highway Safety Manual. • 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. Here, the user will need to examine the data formats for variables in their crash file to identify variables and codes within variables that can be used in determining whether or not each crash in the file is a “target crash.” Crash databases often categorize crash data for a given crash into up to three subfiles – general accident/crash variables, variables for each vehicle in the crash, and variables for each occupant in the crash. The variables needed to determine whether a crash is a “target crash” or not for roadway-segment-based crashes can usually be found in one of the first two subfiles – crash or vehicle data. Crash files differ from juris- diction to jurisdiction. While certainly not always the case, the following variables (or similar variables) listed in Exhibit IV-2 will be used in this determination. • Computerized roadway inventory data and/or intersec- tion inventory data that can be linked to the crash data by location of the crash. Most state DOTs have computerized roadway inventory files for the full state highway system that can be linked to crashes, since both the homogeneous segments in the inventory file and the crashes are identified by “ad- dresses” – usually route and milepost or GIS coordinates. Most local jurisdictions (i.e., counties, towns, townships, cities) do not have such an inventory system. For jurisdic- tions that do not have an inventory file, Procedures 2A and 2B below can be used. • A network screening computer program which will ex- amine a fixed-length portion of each route (e.g., 1 mile) and calculate the number of target crashes (e.g., run-off- road crashes, curve-related crashes) that have occurred in each “window” in the past 3 to 5 years. This program exists in some jurisdictions, but may not exist in others. If not, a knowledgeable computer analyst can build one. The process/program will require that counts of target crashes can be made and “attached to” each homogeneous section on a route, and that each seg- ment includes a “segment length” variable. The program must then be able to examine each segment, starting from the first segment on a route, and accumulate both target crash counts (by adding up the numbers in the segment- specific counters) and segment length (by adding up the individual segment lengths). When the total accumulated segment length reaches the window length (e.g., 1 mile), the total number of crashes is recorded in an output file, along with the route number, the beginning milepost of the first homogeneous segment analyzed, and the ending milepost of the final segment analyzed in the current win- dow. The program would then begin again the accumu- lation of target crash counts and segment lengths on the next homogeneous section of the route, and would repeat the same process until the full route has been completed. The process would be repeated for all routes in the system. Most current highway agency network screening programs operate in a database environment. Efforts are underway 30 Crash Type Variable Crash Database Subfile Run-Off-Road (ROR) Crashes Accident/Crash Type Crash Manner of Collision Crash Sequence of Events Crash or Vehicle First Harmful Event Crash Most Harmful Event Vehicle Crash Location (Off-road) Crash Number of Vehicles or Units Crash Run-Off-Road Crashes into Trees and Utility Poles Same as ROR plus Object Struck Most Harmful Event Vehicle (Sometimes Crash) Vehicle Lane-departure Crashes on Curves Same as ROR Crashes plus Location Type Crash (Sometimes Vehicle) Head-On Crashes Accident/Crash Type Crash Sequence of Events Crash or Vehicle First Harmful Event Crash Most Harmful Event Vehicle Exhibit IV-2. Crash variables and subfile location by crash type.

to develop network screening programs that operate in a GIS environment as well. • Computerized traffic count data that can be linked to the roadway inventory data (unless they are already con- tained in the same database). While the procedure can be operated without comput- erized count data, these data are almost always available in state DOT files that have a roadway inventory system. This is not always the case in urban systems. If available, the traffic count information can be used to further target the potential treatment sites in two ways. First, if the user only wishes to treat “high-traffic” sites, these data can be used to screen out “low-traffic” roadway segments prior to run- ning the network screening program. Second, after the program has been run, the identified sites can be further screened by a given AADT level, or the sites can be sorted by AADT to assist the user in final site choice. • Unit cost for each treatment – both original implemen- tation costs and annual maintenance costs The guides do not provide treatment costs due to differ- ences between states and expected changes over time. The user will need to obtain information on such costs, either from vendors or from other jurisdictions that have used the treatment. The guides do provide “Information on Agencies or Organizations Currently Implementing This Strategy” that could be contacted for help under each of the treatment strategies. (The guides provide only early users, and surrounding jurisdictions may have implemented the treatment after the guide was completed.) Finally, the user will need an estimate of annual maintenance cost per mile for each treatment to be analyzed. Since maintenance in- cludes “replacement after a crash” in some cases, the user may have to make estimates of the number of expected crashes per year and the amount of expected damage. Again, past users of the treatment can be of assistance here. Procedure The general procedure for choosing and targeting treat- ments with known effectiveness levels was provided in Sec- tion III above. The following text will expand that description while focusing on roadway-segment treatments designed to reduce lane-departure crashes. Because the user needs to understand the computerized procedure in order to input the correct values and tailor it for their own jurisdiction, the following provides the details of each step and sub-step. 1. Specify the types/classes of roadway segments that are potential targets for the treatments. Because the choice of treatments, the treatment effec- tiveness, and the treatment cost per unit length may dif- fer by roadway class/type, the user will need to specify the types/classes of interest, such as two-lane rural road seg- ments, multi-lane urban segments (perhaps by number of lanes), or rural interstate segments. If desired, these potential treatment segments could be further screened by AADT level (e.g., only “high-traffic” segments). 2. Develop critical crash frequencies for each candidate treatment type (e.g., shoulder rumble strips) for each roadway class of interest. The “critical frequency” is the frequency of target crashes per mile that, if treated, will result in crash-injury reductions whose economic ben- efit will exceed implementation costs by some factor. In the example presented in the FHWA Sample Plan (24), the target B/C ratio used was 2.0 or greater. These “critical frequencies” must be developed for each candidate treatment being examined. If the same treatment is to be used on different roadway classes, it will be necessary to develop different critical frequencies for each treatment by roadway class if the treatment cost per unit length or treatment effectiveness varies by road- way class. The following formula is used: CF = (Ann. Cost)(Target B/C)/(Eff)(Avg. Crash Cost) Where: • CF = Critical annual frequency of target crashes per unit length to consider the strategy to be cost effective. • Ann. Cost = The annual cost of the improvement per unit length (e.g., per mile). If it is a construction im- provement, it is the construction costs annualized over the expected life of the improvement. Note that if the treatment strategy is related to horizontal curves, then the cost required here is annual cost per unit length of curve (e.g., cost per mile of curve). If the treatment strategy is an education or enforcement treatment, the annual cost can be expressed on a per-unit-length basis if the treatment is to apply to a specific road segment or corridor, but may also cover an entire geographic area or road system to which the treatment is applied (e.g., if the treatment for run-off-road [ROR] crashes is jurisdiction-wide in nature). • Target B/C = The B/C ratio defined by the user. It is usually between 1.0 and 2.0. In the FHWA Sample Plan (24), a value of 2.0 is used. • Eff = The estimated effectiveness of the treatment strat- egy in reducing targeted crashes, expressed as a propor- tion (i.e., the CRF/100). This can be extracted from the FHWA Sample Plan (24) or from other sources. • Avg. Crash Cost = The average economic cost per crash for the target crash type that will be affected by this treat- ment strategy. The following were extracted from Table 10 of Crash Cost Estimates by Maximum Police-Reported Injury Severity Within Selected Crash Geometries (22) and represent “comprehensive costs” in terms of 2001 31

dollars. Comprehensive cost estimates include not only the monetary losses associated with medical care, other resources used, and lost work, but also non-monetary costs related to the reduction in the quality of life. The cost for each crash type is shown in Exhibit IV-3 for two ranges of speed limits – ≤ 45 mph and ≥ 50 mph. The former should be useful for urban crashes, and the lat- ter for rural crashes. 3. Using the inventory file, stratify potentially treatable roadway segments by roadway class. This stratification will result in a file of roadway seg- ments sorted by route number for each of the roadway classes under consideration for treatment. 4. Link target crashes with roadway segments from the appropriate inventory data file, and then perform a computer screening of all segments on all routes that are potential treatment locations to determine which segments have crash frequencies that exceed the criti- cal crash frequencies calculated above. This will be done using the network screening pro- gram described above, and will be done independently for each of the roadway types under consideration. The network screening program will need to output the route number and beginning and ending milepost for each 1- mile segment that exceeds the critical crash frequency. Note that if the treatment being considered is for hor- izontal curves (i.e., the user is searching for a “system” of horizontal curves to correct with, say, improved curve warnings), this step will require that the user’s roadway inventory system can identify the locations (routes and begin/end mileposts) for horizontal curves. If no curve in- ventory data are available (as will unfortunately be the case in most jurisdictions), then the user will have to use either Procedure 2A or 2B instead of this Procedure 1. 5. Correct the output for “treatment gaps” along the same route resulting from the network screening computer program. This correction will require that the user manually examine each of the routes under consideration within each roadway class to detect possible “treatment gaps.” Here the user will need to have the network screening program output the locations of the originally chosen treatment sites, enter these sites into some type of spread- sheet – one treatment segment per row, and then sort the rows by route and beginning milepost. By scanning down this listing for each route under consideration, the user can determine where the treatment gaps are located along each route – the missing segments in the listing. (Note that some of these missing segments would result from the fact that the roadway class changed within the route – e.g., from two-lane to four-lane. This determina- tion will have to be made by comparison with informa- tion from the inventory file on the route in question.) This correction for missing segments within the same roadway class will be needed because the network screen- ing will only detect segments along a given route that exceed the critical crash-frequency threshold. In almost all cases, this will leave treatment gaps along a given route within the same roadway class – segments that do not meet the threshold. The user will need to determine whether or not these below-threshold segments should be treated. The logical first answer is “no,” since the seg- ments did not meet the critical threshold. However, there may be times when all or some of these gaps should be included in the treatment program. First, it may be illogical to leave isolated gaps untreated on a given route if the gaps have basically the same road- way and roadside characteristics and AADT as the adjacent treatment sites. The network screening program is exam- ining a certain past period of crashes (e.g., the past 5 years). Crashes, particularly run-off-road and head-on crashes, are usually low-frequency events per mile, and the loca- tion of a crash in a given time period may be somewhat random. Thus, if a different 5 years of data were chosen, the chosen treatment locations might be slightly different. These factors will produce such treatment gaps. The user will have to make a judgment concerning whether to treat the gaps, and there are no precise guidelines for making this judgment. As general guidance, if a long section of a route has very few treatment gaps (i.e., most of the segments on the route are identified by the network screening program), and if the user knows that the gaps are very similar to the surrounding treatment sections in terms of AADT and roadway and roadside characteristics, then it would appear logical to treat those gaps also. If there are more “gaps” than “treatments” on a given route but the gaps and treatment segments are similar in terms of AADT and characteristics, then the user might either decide to just treat the originally chosen sections, or not to treat this route at all. Second, there may also be situations where the logical length of the treatment may be greater than 1 mile. For 32 Crash Type Speed Limit Category Comprehensive Cost/Crash* < 45 mph $67,000 Run-off-road crashes involving trees or other roadside objects > 50 mph $107,000 < 45 mph $148,000 Run-off-road crashes involving rollover as the primary impact type > 50 mph $256,000 < 45 mph $60,000 Head-on crashes > 50 mph $613,000 * Costs in 2001 dollars Exhibit IV-3. Crash cost by crash type and posted speed limit (22).

example, an agency may decide that shoulder rumble strips will be installed only with repaving, and that repaving is not done in roadway sections of less than X miles (with X greater than 1 mile). The first option here would be to change the length of the window in the net- work screening program to the minimum project length. However, since the window jumps from point to point along the route (e.g., from the beginning of mile 1 to the beginning of mile 2), the longer the window, the more likely that concentrations of target crashes that fall at the ends and beginnings of adjacent sections will be split into two parts, and thus each part will fall below the critical frequency. An alternative strategy is to use the 1-mile window as originally suggested, and to conduct the same examination as above if there are limited gaps among many treatment segments. The user could also examine the identified treatment sites to see where groups of 1-mile section equal or exceed the minimum project length, and then add additional adjacent segments if their AADT and characteristics are similar to the treatment group sites. In summary, there are no hard-and-fast guidelines concerning how to correct for treatment gaps within the same roadway class. The decision will have to be made by the user, and the rules for making the decision may change from project to project and treatment to treat- ment. In general, it would appear that the best decision will be at least partially based on similar AADT and sim- ilar characteristics. 6. Estimate the expected crash/injury reductions on all the identified target locations. The results of this step will be used in Step 9 below to determine whether or not the goal is reached. Here, for each treatment segment within a given roadway class identified at the end of Step 5 (i.e., after correction for treatment gaps), the user will need to determine the number of crashes and injuries that will be reduced by this treatment. This will be done by summing up all per- tinent crashes or crash injuries for all segments to be treated, and then multiplying this total by the estimated effectiveness level for the treatment under consideration. CI reduction = (CI on segments) × Eff Where: CI = “Goal-related” crashes or crash injuries Eff = treatment effectiveness The definition of “goal-related” crashes or injuries is, as implied, based on the nature of the overall goal that has been established. If the goal is oriented to fatal and injury target crashes, then these will be accumulated. If the goal is total target crashes, then these will be accumulated. The summing of goal-related crashes or injuries will be done by using a computer program to estimate the annual number of such target crashes for all unit-length segments chosen for treatment. Users with full crash and inventory systems who have developed the network screening pro- gram will have the ability to link such goal-oriented tar- get crashes to each segment chosen and to sum the total over all segments. The best annual estimate will be one based on more than 1 year of past data (usually 3 to 5 years) and then dividing by the number of years used. 7. Repeat the above steps for each potential treatment type. The above steps are then repeated for the second and subsequent potential treatment types. In each case, criti- cal crash frequencies are calculated for each roadway class, the network screening program is used to identify treatment segments, and corrections are made for treat- ment gaps. However, a final correction is needed for segments that have been identified for more than one treatment type, as detailed in the following step. 8. Correct for multiple treatments on the same segment. Since many segment-based treatments affect the same type of target crash (e.g., shoulder rumble strips and shoulder widening both can affect run-off-road crashes), the above procedure will identify the same segment as a potential for treatment in many cases. In these cases, the user has two options: (1) choose only one treatment for each of these segments, or (2) choose to implement two or more treatments on the same segment. Under Option 1, the user would compare the lists of potential treatment segments (after correction for gaps) from Step 5 above, and would decide which treatment to place on each segment where two or more treatments could be implemented. That segment (and its related goal-oriented crashes or injuries) is then removed from the list of segments for all other treatments. Under Option 2, the user must develop some measure of combined effectiveness for the two or more treatments to be applied to a given segment. Since the combined effec- tiveness of two treatment strategies on the same location will not be the simple sum of the two effectiveness levels, some correction must be applied for the second and all subsequent treatments that are applied to the same seg- ment. Unfortunately, there is little knowledge available about the combined effects of multiple treatments. Until that knowledge is developed, it is suggested that the effec- tiveness level (Eff) of the second treatment applied to a given section be reduced by 50 percent, and the effective- ness of the third treatment and subsequent treatments ap- plied to the same segment be reduced to 25 percent of their expected effectiveness when used alone. For example, assume that the first treatment for a given segment has an effectiveness level of 0.2, the second has an effectiveness level of 0.15, and the third has an effectiveness level of 0.10, and the fourth and subsequent treatments add no addi- 33

tional effectiveness. The estimated combined effectiveness of the three treatments applied to the same segment would be 0.2 + 0.15(.5) + 0.1(.25) = 0.3. Again, this is only an es- timate of the true combined effectiveness at best. 9. Sum all expected crash injury reductions for all chosen treatment types and chosen target locations and com- pare that total to the established goal. 10. Add 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. Again, the example draft plan presented at the FHWA web site (http://safety.fhwa.dot.gov/roadway_dept/docs/ lanedeparture/index.htm) provides additional discussion of this option. Procedure 2A – Choosing Roadway-Based Treatments and Target Populations When Treatment Effectiveness Is Known and Mileposted Crash Data Are Available, but Detailed Inventory Data Are Not Available The following text identifies the data needed for conduct- ing Procedure 2A, followed by the individual steps in the procedure. Note again that this procedure requires “mileposted” crash data. If mileposted crash data are not available, refer to Procedure 2B or 3. Data Needs The data needed for Procedure 2A are virtually the same as for Procedure 1, except that neither detailed roadway inventory data nor linkable traffic counts are required. (Note that this pro- cedure operates more accurately if the user can not only sort crashes by route and milepost, but also has some inventory information or knowledge that will allow him/her to determine which route-milepost ranges are rural vs. urban, the number of lanes, and whether the roadway is divided or undivided. This will be covered in the steps of the procedure below.) The following are the specific data needed to use Procedure 2A when choosing and targeting roadway-based treatments. A descrip- tion of each item is provided under Procedure 1 above and will not be repeated here. • A specified effectiveness level (CRF or AMF) for each treatment to be examined. • A computerized crash data file that includes sufficient crash details to isolate target crash types (run-off-road, head-on crashes, run-off-road on curves, etc.) and poten- tial target populations that will be affected by each treat- ment, and which is “mileposted” such that the location of each crash is included. As noted in the procedure below, it is also advantageous if the crash data contains information that can be used to define “roadway class or type” – e.g., information on num- ber of lanes, route type, divided vs. undivided, or any other roadway class characteristics. Since no detailed roadway inventory exists in this situation, these data will help in defining potential target locations within different road- way classes or types. • 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) that have occurred in the past 3 to 5 years. Note that this program is different from the network screening program in Procedure 1, because it is applied to mileposted crash data for which no roadway-segment-based inventory data is available. If such a program does not cur- rently exist in a jurisdiction, it can be developed by a knowl- edgeable computer analyst familiar with crash data files. In general, the program will need to accumulate a count each time a target crash is found, the milepost for each crash reached, and the distance from the last crash (e.g., the differ- ence between the two mileposts) for each adjacent pair of crashes. The program will then accumulate the target crash count and cumulative distance until the distance is equal to or greater than the specified window length (e.g., 1 mile). If the accumulated distance is equal to 1 mile, which is un- likely, the program will output the number of target crashes and the milepost of the first and last crashes encountered in that length and the distance between the first and last crash, in this case, 1.0 mile. If the accumulated distance is greater than 1 mile (i.e., the 1-mile limit fell between two adjacent crashes), the counter should subtract the last crash added (i.e., the one outside the 1-mile limit), and should again output the number of target crashes in the window, the milepost for the first crash and last crash remaining in the window, and the distance between the first and last crash, which may be less than 1 mile in this case. A new window would then begin with the current crash being considered (i.e., it would be counted and its milepost recorded) and the process would proceed until the route ends. Each time the specified window length is reached and output is produced, the count will be compared to the critical frequency calcu- lated in Step 2, and will only be retained in the final output file if the count exceeds the critical frequency. • Unit cost for each treatment – both original implementa- tion costs and annual maintenance costs Procedure The general procedure for choosing and targeting treat- ments with known effectiveness levels was provided in Section 34

III above. The following text will expand that description while focusing on roadway-segment treatments – those de- signed to reduce lane departure crashes. Because the user needs to understand the computerized procedure in order to input the correct values and tailor it for their own jurisdiction, the following provides the details of each step and sub-step. 1. Develop critical crash frequencies for each candidate treatment type and roadway class of interest. The “criti- cal frequency” is the frequency of target crashes per mile that, if treated, will result in crash-injury reductions whose economic benefit will exceed implementation costs by some factor. The same formula and information presented under Step 2 of Procedure 1 above will be used here. However, if the user is attempting to target horizontal curve treatments without an inventory file that defines the beginning and ending mileposts for each curve, a different “annual cost per unit length” will have to be used. Here, the user will have to estimate the average length of curve in his jurisdiction, and will then estimate the annual treat- ment cost of that length. It is suggested that if there are dif- ferent types of terrain in a jurisdiction (e.g., mountainous vs. level terrain) that would significantly affect the average curve length, the user would estimate an average length and cost for curves in each terrain type. 2. Sort crashes by route and milepost in ascending order, and then perform a computer screening of all segments on all routes that are potential treatment locations to de- termine which segments have target crash frequencies that exceed the critical crash frequencies calculated in Step 2. This screening will be done using the network screen- ing program described above. If crash-based information is available on roadway class or type (e.g., number of lanes, route type, divided vs. undivided), the target crash defini- tions should include these variables (e.g., run-off-road crashes on two-lane roads and head-on crashes on divided roads). The screening will then be done independently for each of the roadway types (as defined by crash variables) under consideration. As noted above under “Data Needs,” the network screening program will need to output the total number of target crashes in the specified length, and the route number and mileposts for the first and last crash falling in each “window” for which the total number of target crashes exceeds the critical crash frequency. Note that if the treatment being considered is for hori- zontal curves (for example, the user is searching for a “system” of horizontal curves to correct with improved curve warnings), the window length should be defined as the expected maximum (not average) curve length in a given terrain. The use of target crashes that are only curve- related will lead to acceptable results in this screening ef- fort, even for shorter than maximum-length curves. 3. Correct the output for “treatment gaps” along the same route resulting from the network screening computer program. If this step is done, the user will follow a “manual re- view” procedure similar to that described under Step 5 of Procedure 1. The rationale for this step is provided there. As before, this correction will require that the user manu- ally examine each of the routes under consideration within each roadway class to detect possible treatment gaps. Here, the user will take the output of the network screening program (i.e., the route and locations of the originally chosen treatment sites), enter these sites into some type of spreadsheet (one treatment window per row), and then sort the rows by route and beginning milepost. By scan- ning down this listing for each route under consideration, the user can determine where the treatment gaps are located along each route – the missing segments in the listing. (Note that some of these missing segments would result from the fact that the roadway class changed within the route – e.g., from two-lane to four-lane. This determi- nation will have to be made based on the user’s knowledge of where the roadway class changes along a given route.) However, because there is no inventory data available under this procedure, the user will not have inventory data that provides detailed information on the AADT levels and roadway characteristics of the treatment gaps adjacent to the identified treatment windows. This determination will have to be based on the user’s knowledge of the route in question. If such knowledge is available, the user will identify additional, similar treatment segments for each treatment/road class combination. 4. Estimate the expected crash injury reductions on all the identified target locations. Just as in Procedure 1, the results of this step will be used in Step 8 below in determining whether or not the goal is reached. Here, for each treatment window identi- fied at the end of Step 3 (i.e., after correction for treatment gaps), the user will need to determine the number of crashes and injuries that will be reduced by this treatment. This will be done by summing up all pertinent crashes or crash injuries for all windows to be treated, and then mul- tiplying this total by the estimated effectiveness level for the treatment under consideration. CI reduction = (CI on segments) × Eff Where: CI = Goal-related crashes or crash injuries Eff = treatment effectiveness Just as in Procedure 1, the definition of “goal-related” crashes or injuries is, as implied, based on the nature of the 35

overall goal that has been established. If the goal is ori- ented to fatal and injury target crashes, then these will be accumulated. If the goal is total target crashes, then these will be accumulated. The summing of goal-related crashes or injuries will be done by estimating the annual number of such target crashes for all segments (windows) chosen for treatment (after correction for treatment gaps). While it was rela- tively simple to add in the additional crashes from the “gap-filling” segments with a full inventory file in Proce- dure 1, this is not as simple here, since the network screen- ing program used in this procedure does not output seg- ments other than those meeting the crash frequency threshold. It is suggested that in this case, the annual num- ber of goal-oriented crashes from the identified treatment segments be used to estimate the additional number that would occur on the added treatment gap segments. As noted above, the network screening program can be developed to output the total number of target crashes in each window chosen for treatment and the (approximate) length of each chosen treatment window. The estimate of annual target crashes (or injuries) per mile in these chosen windows is: Where: The user can also manually calculate the number of miles of treatment gaps that he or she adds for treatment in Step 3. The number of goal-related target crashes for these segments can be estimated by multiplying the total length of these new segments by CI in the above formula. 5. Repeat the above steps for each potential treatment type. As in Procedure 1, the above steps are then repeated for the second and subsequent potential treatment types. In each case, critical crash frequencies are calculated for each roadway class, the network screening is used to identify treatment segments, and corrections are made for treat- ment gaps. However, a final correction is needed for segments that have been identified for more than one treatment type, as detailed in the following step. 6. Correct for multiple treatments on the same segment. The user will again need to correct for multiple treat- ments on the same segment. The same rationale and pro- cedure followed in Procedure 1 will be followed here. (See Step 8 of Procedure 1). Annual Target Crashes = Sum of all target crashes in chosen windows Number of years of crash data used in the sample CI = Annual Target Crashes Sum of window lengths 7. Sum all expected crash injury reductions for all chosen treatment types and chosen target locations and com- pare that total to the established goal. 8. Add 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. Again, the example draft plan presented at the FHWA web site (http://safety.fhwa.dot.gov/roadway_dept/docs/ lanedeparture/index.htm) provides additional discussion of this option. Procedure 2B – Choosing Roadway-Based Treatments and Target Populations When Treatment Effectiveness Is Known and Neither Mileposted Crash Data nor Detailed Inventory Data Are Available The following text identifies the data needed for conducting Procedure 2B, followed by the individual steps in the proce- dure. Note again that since no mileposted crash data exist, this procedure will only allow the user to identify entire routes within a given jurisdiction as potential treatment routes, but not segments of routes. It will also not allow the user to target the treatments to specific locations along the route. Data Needs The data needed for Procedure 2B are less than required in either of the previous two procedures. Major differences in- clude the fact that no inventory or traffic data are required, and that the crashes do not have to be “mileposted” to a specific location on a specific route. However, each crash record must contain information on the county or local jurisdiction and the name of the route/street where the crash occurred. • A specified effectiveness level (CRF or AMF) for each treatment to be examined. See discussion of this issue under Procedure 1. • A computerized crash data file which includes sufficient crash details to isolate target crash types that will be af- fected by each treatment (run-off-road, head-on crashes and run-off-road on curves), and potential target popula- tions. Each crash record must contain a county or jurisdic- tion name where the crash occurred, and the name of the route or road where the crash occurred. • “Route length” information that will provide the length in miles of each road or route within a county or local jurisdiction that is a potential target for any treatment, or at least the approximate length. If this information is not available in the user’s files, it may be available from other sources including road maintenance records, and can be scaled from maps if necessary. 36

• Unit cost for each treatment – both original implemen- tation costs and annual maintenance costs See discussion of this issue under Procedure 1. Procedure The following steps are those that would be followed for choosing among roadway-segment treatments with known effectiveness and targeting these treatments to entire routes in a jurisdiction. 1. Develop critical crash frequencies for each candidate treatment type and roadway class of interest. The “crit- ical frequency” is the annual frequency of target crashes per mile that, if treated, will result in crash- injury reductions whose economic benefit will exceed implementation costs by some factor. The same formula and information presented above under Step 2 of Procedure 1 will be used here. 2. Link target crashes to each route in each jurisdiction (but not to a specific point on the route). This will require computer sorting of crashes by each named route. Some manual effort will be required to correct misspelled names and to group routes or streets that have multiple names. The output of this program will be a listing of target crashes sorted by route name. Note that multiple years of crashes can be used, and in- deed the procedure will be more accurate if more than 1 year’s crash data (e.g., 3 to 5 years) are used. If multi- ple years are used, there may be situations where a route was renamed during the period. If so, both crashes with the original and new name should be accumulated under one route name. 3. Develop a spreadsheet that contains the count of target crashes for each route (one route per row), along with the mileage for that route. It may be possible for the computer program used to sort the crashes in Step 2 to output this count for each route. If not, the counts can be made manually. The final output of this step is a spreadsheet containing a total count of target crashes and the length in miles for each route under consideration. 4. Calculate the annual crash frequencies per mile for each potential route. If a spreadsheet is used, this is a simple step in which the crash count is divided by the route length times the num- ber of years of crashes used. 5. Identify routes to be treated by determining which have calculated annual frequencies per mile that exceed the developed critical crash frequencies per mile. This is a comparison of the output of Step 4 with the “critical frequencies” defined in Step 1. 6. Estimate the expected crash injury reductions on all the identified target routes. Just as in Procedure 1, the results of this step will be used in Step 9 below in determining whether or not the goal for the jurisdiction is reached. Here, for each treat- ment route identified at the end of Step 5, the user will need to determine the annual number of crashes and in- juries that will be reduced by this treatment. This will be done by summing up all pertinent crashes or crash in- juries for all routes to be treated, and then multiplying this annual total by the estimated effectiveness level for the treatment under consideration. CI reduction = (CI) × Eff Where: CI = Annual “goal-related” crashes or crash injuries on the routes chosen Eff = treatment effectiveness Just as in Procedure 1, the definition of goal-related crashes or injuries is, as implied, based on the nature of the overall goal that has been established. If the goal is oriented to “fatal and injury” target crashes, then these will be accumulated. If the goal is total target crashes, then these will be accumulated. The annual estimate of potentially treatable crashes or injuries can be extracted from the spreadsheet output in Step 3. For the routes chosen, divide the total crashes on each route by the number of years of data, and then sum across all chosen routes. 7. Repeat the above steps for each potential treatment type. As in Procedures 1 and 2A, the above steps are then re- peated for the second and subsequent potential treat- ment types. 8. Correct for multiple treatments on the same route. The user will again need to correct for multiple treat- ments on the same route. In general, the same rationale and procedure followed in Procedure 1 will be followed here. (See Step 8 of Procedure 1.) However, in this case, cor- rections are made on a route-basis rather than a route- segment basis (i.e., either one treatment is specified for a given route and that route is removed from other treat- ment groups, or a correction in effectiveness is made for the second and subsequent treatment on the same route). 9. Sum all expected crash injury reductions for all chosen treatment types and chosen target routes and compare that total to the established goal. 10. Add 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. Again, the FHWA Sample Plan for lane departures (24) provides additional discussion of this option. 37

Procedure 3 – Choosing Roadway Treatments and Target Locations When Treatment Effectiveness in Terms of Crash/Injury Reduction Is Not Known As noted in the preceding section, the three procedures described above allow the user to choose roadway-based treatments and treatment targets for a given problem while ensuring that the economic value of the crash/injury reduc- tions will exceed the cost of implementing the program. All three 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 Pro- cedures 1, 2A and 2B are not possible for these treatments. This Procedure 3 is intended to help the user make an edu- cated choice of which treatments will be most effective in their jurisdiction, and to help the user develop a targeting strategy for the treatment in cases where it is not to be applied jurisdiction-wide (e.g., where specific routes or route seg- ments are to be targeted). In general, the choice between al- ternative roadway-segment treatments will be based on the specific nature of the lane-departure crash problem, and the choice of target locations will be based on the determination of where the crash/injury problem of interest is found. A dis- cussion of this more general procedure is included under the Procedure 3 subheading in Section III, and the reader should review that section. 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 esti- mate a specific CRF or AMF value. In a case for which the an- alyst 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. Data Needs The only required data for Procedure 3 are crash data that will allow the user to specify target crashes for each roadway- segment treatment under consideration (see Exhibit IV-1 in the “crash data” description under Procedure 1). However, in order to target the treatment to specific routes or route sections, the crash data must be “mileposted” or at least contain infor- mation on the county and route. The availability of roadway inventory data that can be linked to the crash data will improve both the treatment choice and the treatment targeting. Procedure As described in Section III, Procedure 3 has two basic steps: • First, choose the best treatments (i.e., the roadway- segment treatments most likely to be applicable in a given jurisdiction) from among the set of all roadway-segment treatments presented in the applicable NCHRP Report 500 guides. • Second, choose the routes or route segments to which the selected treatments should be applied. As described earlier in more detail, the choice of the best treatments from the listing of many potential roadway-segment treatments can be based on the following factors: a) The potential treatment judged to be the most effective, given that effectiveness is unknown b) The relative magnitude of the crash types and severity levels that the treatment will affect c) The cost of the potential treatments per mile d) Other technical or policy considerations These factors must be combined in some fashion to decide which treatment to choose. While there are multiple ways of making this choice, the following represents one such procedure. 1. Prioritize the specific roadway-segment problem(s) to be addressed. This is related to Factor b in the above list. Here, 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 di- vided roads, freeways). This prioritization will be based on the frequency and severity of the specific types of lane- departure crashes occurring in a user’s jurisdiction. Tar- get crash types for each roadway-segment treatment were defined under Procedure 1. 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 injury 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 38

severity level within 22 different crash types including different types of run-off-road and head-on crashes can be found in Crash Cost Estimates by Maximum Police- Reported Injury Severity Within Selected Crash Geometries (22). This analysis of total crash cost will provide the user with overall information on which lane-departure crash type is most important. 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 which can be used in a less detailed analysis (e.g., number of lanes, rural vs. urban, route type). This analysis will then produce a listing of potentially treatable roadway-segment 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 circumstances (e.g., nighttime vs. daytime distributions of total crash cost). 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-prior- ity crash type. The user will then review the pertinent NCHRP Report 500 guides and list treatments that would be most appro- priate for each of the high-priority crash types identified 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 total crash cost related to each potential treatment strategy could be developed by specifying the crash types that are most likely to be affected by each strategy (e.g., nighttime 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. However, for a given set of possible treatments for a par- ticular crash-type/road-class combination, it may be possible 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 assume that rumble strips on two-lane rural roads would be more effective than wider edge lines or raised delineators. At times, this will clearly be a very dif- ficult judgment to make. 4. Choose “best” treatment(s) by considering estimated effectiveness, cost per mile 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 de- cision on which treatment(s) to implement – the cost per mile of the treatment and other technical and policy con- siderations. 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 factors, 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 judg- ment. 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 treat- ments, with the nature of the treatment defining the spe- cific crash types more likely to be affected (e.g., raised de- lineators 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 treatment 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 subpopulation or location where the treatment is to be applied • Cc = average economic cost per target crash • Eff = treatment effectiveness, or the percent reduction in target crashes B Ct ≥1 0. 39

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 where the problem is found. Since this procedure concerns treatment strategies without known effectiveness, it will not be possible to tar- get the 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 or routes showing the highest total crash cost or frequency, coupled with user judgment concerning the nature of the roadway and roadside at potential target locations and technical and political issues. If the crash data are mileposted, the user could (1) link crashes to routes and search for the lo- cations of “clusters” of target crashes for possible treat- ment, or (2) use a network screening program similar to that described under Procedure 2A to identify 1-mile sec- tions with the highest crash frequency or crash burden (by weighting each crash by its economic cost and summing total crash cost within each window). The windows iden- tified by the network screening program could then be ranked by frequency or total crash cost to identify priority locations. The user would then correct for “treatment gaps” using the same logic provided in Procedure 2A. If the crashes are not mileposted, but there is informa- tion available on jurisdiction and route, the user could link crashes to routes within the jurisdiction and calculate the total crash cost or number of target crashes per mile by dividing the sum of the crash cost or the sum of target crashes on that route by route length. The user can then rank the potential routes for treatment based on this rate per mile, and choose the routes to be treated based on the highest rankings plus other technical and policy factors. 6. Decide what to do with multiple treatments on the same segments/routes. The above steps could possibly produce roadway loca- tions or routes within a jurisdiction that could be treated with multiple treatments. Unlike the earlier procedures where it was possible to estimate combined effectiveness for multiple treatments on the same segments or routes, since treatment effectiveness is not known here, the user will have to use other factors in the final treatment choice for these lo- cations. If the potential treatment strategies still under con- Eff C N C t c = * sideration are characterized by different target crash types (e.g., tree-related crashes vs. total run-off-road crashes), and if the crash data are mileposted or include route informa- tion, the user could use the outputs of Step 5 above in mak- ing the targeting decision. Step 5 produced total crash cost or crash frequency of each potential target section or route. For each segment or route where multiple treatments are possible, the user could compare the crash frequency or total crash cost for each of the different possible strategies. Total crash cost will be a much superior criterion if the target crash types being compared differ with respect to crash severity. If total crash cost or frequency for one treatment strategy clearly exceeds total crash cost or frequency for the other, the first would be a logical treatment choice. If the total crash cost or frequency for the different strategies is essentially the same, the user will need to make the decision based on “best judgment” (e.g., which treatment is being used on adjacent roadway segments). 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 fund- ing 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 treatments types and treat- ments until the available budget for safety improvement has been fully committed. The total benefit of the selected program will not be forecastable, but the success of the program can be determined 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 meas- ures are not available (tried treatments) should then be considered. Experimental treatments may have a modest role 40

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, 2A, 2B, and 3 described above. Procedure 1. Determine if proven treatments can meet the established goal. Consider treatments with known effectiveness meas- ures (proven treatments) using either Procedure 1, 2A, or 2B as appropriate, depending on the types of data avail- able. 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. This step would involve consideration of treatments with- out known effectiveness that have been used extensively by highway or driver/vehicle agencies (tried treatments). If it is possible to estimate the effectiveness of these treatments 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 effective- ness of treatments without known CRFs or AMFs. Note that estimating treatment effectiveness is very difficult and can lead to poor treatment choices unless the esti- mates are realistic. This estimation was not suggested in Procedure 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 following 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 sim- ilar treatments if they exist. For example, a CRF ex- ists 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 marking) 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. 4. Consider additional tried treatments. For treatments for which reliable effectiveness measures cannot be estimated in Step 3, apply Procedure 3 to select additional treatment types and target locations until all available funds have been budgeted. 41

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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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