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50 6. Estimate the expected crash injury reductions on all the Procedure 3 Choosing Intersection identified target routes. Treatments and Target Locations Just as in Procedure 1, the results of this step will be When Treatment Effectiveness in used in Step 9 below in determining whether or not the Terms of Crash/Injury Reduction goal for the jurisdiction is reached. Here, for each treat- Is Not Known ment route identified at the end of Step 5, the user will need to determine the annual number of crashes and in- As noted in the preceding section, the three procedures juries that will be reduced by this treatment. This will be described above allow the user to choose intersection treat- done by summing up all pertinent crashes or crash in- ments and treatment targets for a given problem while en- juries for all routes to be treated, and then multiplying suring that the economic value of the crash/injury reduc- this annual total by the estimated effectiveness level for tions will exceed the cost of implementing the program. All the treatment under consideration. three procedures require that the treatments being examined each have a known level of effectiveness expressed in terms CI reduction = (CI) Eff of an expected crash/injury reduction a defined CRF or Where: AMF. Unfortunately, many of the intersection treatments in CI = Annual "goal-related" crashes or crash injuries on the NCHRP Report 500 guide series do not have defined lev- the routes chosen els of effectiveness. Thus, economic analyses like those that Eff = treatment effectiveness are the basis for Procedures 1, 2A and 2B are not possible for these treatments. This Procedure 3 is aimed to help the user Just as in Procedure 1, the definition of "goal-related" make an educated choice of which treatments will be most crashes or injuries is, as implied, based on the nature of effective in their jurisdiction, and to help the user develop a the overall goal that has been established. If the goal is targeting strategy for the treatment in cases where it is not to oriented to fatal and injury target crashes, then these will be applied jurisdiction-wide (e.g., where specific intersec- be accumulated. If the goal is total target crashes, then tions are to be targeted). In general, the choice between al- these will be accumulated. ternative intersection treatments will be based on the specific The annual estimate of potentially treatable crashes or nature of the intersection crash problem, and the choice of injuries can be extracted from the spreadsheet output in target locations will be based on the determination of where Step 3. For the routes chosen, divide the total crashes on the crash/injury problem of interest is found. A discussion of each route by the number of years of data, and then sum this more general procedure was included under the Proce- across all chosen routes. dure 3 subheading in Section III, and the reader should 7. Repeat the above steps for each potential treatment type. review that section. As in Procedure 1 and 2A, the above steps are then re- Procedure 3 is intended for application to tried or experi- peated for the second and subsequent potential treat- mental treatments for which the analyst has decided that there ment types. is likely to be a crash/injury reduction benefit, but for which 8. Correct for multiple treatments on the same route. the analyst does not have sufficient evidence to estimate a spe- The user will again need to correct for multiple treat- cific CRF or AMF value. In a case for which the analyst is able ments on the same route. In general, the same rationale to estimate a specific CRF or AMF value, even if the estimate and procedure followed in Procedure 1 will be followed is only an approximation, it is recommended that Procedure here. (See Step 8 of Procedure 1.) However, in this case 4 be used rather than Procedure 3. corrections are made on a route basis rather than an intersection basis (i.e., either one treatment is specified for a given route and that route is removed from other Data Needs treatment groups, or a correction in effectiveness is made for the second and subsequent treatment on the The only required data for Procedure 3 are crash data that same route.) will allow the user to specify target crashes for each inter- 9. Sum all expected crash injury reductions for all chosen section treatment under consideration (see Exhibit V-1 in treatment types and chosen target routes and compare the "crash data" description under Procedure 1). However, that total to the established goal. in order to target the treatment to specific intersections, the 10. Add new treatments, new targets, or new approaches crash data must be "mileposted" or at least contain (e.g., inclusion of safety treatments in normal mainte- information on the county and route. The availability of nance or rehabilitation efforts) until the goal is met. intersection inventory data that can be linked to the crash Again, the FHWA Sample Plan for intersections (25) data will improve both the treatment choice and the treat- provides additional discussion of this option. ment targeting.

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51 Procedure cost per severity level within 22 different crash types including different types of run-off-road and head-on As described in Section III, Procedure 3 has two basic steps: crashes can be found in Crash Cost Estimates by Maximum Police-Reported Injury Severity Within Selected Crash First, choose the best treatments (i.e., the intersection Geometries (22). This analysis of total crash cost will pro- treatments most likely to be applicable in a given jurisdic- vide the user with overall information on which intersec- tion) from among the set of all intersection treatments pre- tion crash type is most important. sented in the applicable NCHRP Report 500 guides. The user may further refine this analysis by examining Second, choose the routes or route segments to which the crash frequency or total crash cost within intersection selected treatments should be applied. classes. If the crash data are mileposted and linkable in- ventory data are available, details of intersection types can As described earlier in more detail, the choice of the best be linked to each crash record (e.g., number of legs by type treatments from the listing of many potential intersection of traffic control). If inventory data are not available, there treatments can be based on the following factors: may be variables on the crash record itself which can be used in a less-detailed analysis (e.g., name of intersecting a) The many potential treatments judged to be the most road, distance from some landmark). effective, even given that effectiveness is unknown This analysis will then produce a listing of potentially b) The relative magnitude of the crash types and severity treatable intersection crash types (perhaps by intersection levels that the treatment will affect class) that can be sorted by frequency or total crash cost, c) The cost of the potential treatments per mile thus providing a ranked listing. For the higher-ranked d) Other technical or policy considerations crash types, the user can then conduct additional analyses to determine more of the specifics of the crash circum- These factors must be combined in some fashion to decide stances (e.g., nighttime vs. daytime distributions of total which treatment to choose. While there are multiple ways of crash cost). These additional "drill-down" analyses should making this choice, the following represents one such proce- be designed to provide additional information that could dure. lead to the choice of one treatment over another (e.g., raised pavement markers are primarily effective at night or 1. Prioritize the specific intersection problem(s) to be in rainy weather). addressed. 2. Identify possible treatments for use for each high-priority This is related to Factor b in the above list. Here, the crash type. issue is whether to treat angle, sideswipe, run-off-road, The user will then review the pertinent NCHRP Report rear-end, head-on, or other intersection crash types, and 500 guides and list treatments that would be most appro- at which intersection types (e.g., rural three-leg unsignal- priate for each of the high-priority crash types identified in ized intersections, urban four-leg signalized intersections, the above step. The choice should be limited to those treat- etc.). This prioritization will be based on the frequency ment strategies that are classified as tried in the guides. and severity of the specific types of intersection crashes (Proven treatments have known effectiveness levels and can occurring in a user's jurisdiction. Target crash types for be analyzed in one of the three procedures above.) each of the intersection treatments were defined under 3. Rate the possible treatments based on estimated Procedure 1. For each crash type, the user could begin the effectiveness. process by analyzing 3 to 5 years of crash data to determine Since this procedure deals with treatment strategies the frequency of each type. However, since some crash with unknown effectiveness, this appears to be impossible. types are more severe than others (e.g., head-on crashes However, for a given set of possible treatments for a par- are more severe than sideswipe crashes), total crash ticular crash type/intersection class combination, it may frequency alone does not provide the complete answer. be possible to make a judgment concerning which treat- While an alternative is to restrict the analysis to only fatal ment strategy would be expected to be most effective. For and serious-injury crashes, this will severely limit the crash example, for rear-end crashes on high-speed roads, one sample, and will also omit a large component of the crash would assume that left-turn lanes would be more effective problem non-serious injury and no-injury crashes. A than advance warning signs. At times, this will clearly be a better solution is to weight each crash by an economic cost very difficult judgment to make. based on its type and severity, and then accumulate the 4. Choose the "best" treatment(s) by considering esti- total crash cost (i.e., the total economic cost of crashes) mated effectiveness, cost per intersection and other within each target crash type. Information on economic technical and policy considerations.

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52 The user will then combine the output of the steps Since this procedure concerns treatment strategies with- above with at least two other factors in making a final de- out known effectiveness, it will not be possible to target the cision on which treatment(s) to implement the cost per treatments based on any type of economic analysis such as intersection of the treatment and other technical and pol- those in Procedures 1, 2A and 2B. Instead, the treatment icy considerations. Unfortunately, there are no good will be targeted to intersections showing the highest total guidelines for how to "weight" the different factors. While crash cost or frequency, coupled with user judgment problem size (total crash cost) and assumed treatment concerning the nature of the intersection and technical and effectiveness are key factors, there may be technical, political issues. If the crash data are mileposted, the user policy, and cost considerations that will remove certain could (1) link crashes to routes and search for the locations treatments from consideration even if they are felt to be of "clusters" of target crashes for possible treatment, or (2) effective. The user will have to choose the final treatments use a network screening program similar to that described based on "best judgment." The procedure outlined above under Procedure 2A to identify 1-mile sections with the will at least ensure that the major factors in the decision highest crash frequency or total crash cost. The windows are clearly defined. The output of this step will be one or identified by the network screening program could then be more chosen treatments, with the nature of the treatment ranked by frequency or total crash cost to identify priority defining the specific crash types more likely to be affected locations. The user would then correct for "treatment (e.g., left-turn lanes will affect rear-end crashes). gaps" using the same logic provided in Procedure 2A. The user should be able to work backwards using the If the crashes are not mileposted, but there is informa- number of crashes likely to be affected by a given treatment tion available on jurisdiction and route, the user could link and the cost of applying that treatment to a given population crashes to routes within the jurisdiction and calculate the or location (see items b and c described at the beginning of total crash cost or number of target crashes per mile by this procedure) to determine the treatment effectiveness dividing the sum of the crash cost or the sum of target needed to maintain a B/C ratio greater than or equal to 1.0. crashes on that route by route length. The user can then rank the potential routes for treatment based on this rate B 1.0 Ct per mile and choose the routes to be treated based on the highest rankings plus other technical and policy factors. Where: 6. Decide what to do with multiple treatments at the same B = economic benefit of applying a selected treat- intersections/routes. ment to a given location or population The above steps could possibly produce intersections or Ct = the cost of applying that treatment to the routes within a jurisdiction that could be treated with selected location or population multiple treatments. Unlike the earlier procedures where it was possible to estimate combined effectiveness for B = N*Cc*Eff multiple treatments on the same intersections or routes, Where: since treatment effectiveness is not known here, the user N = Number of target crashes for the subpopulation will have to use other factors in the final treatment choice or location where the treatment is to be applied for these locations. If the potential treatment strategies still Cc = average economic cost per target crash under consideration are characterized by different target Eff = treatment effectiveness, or the percent reduc- crash types (e.g., rear-end crashes vs. sideswipe crashes), tion in target crashes and if the crash data are mileposted or include route information, the user could use the outputs of Step 5 Since different severity levels have different crash costs, the above in making the targeting decision. Step 5 produced value used for Cc can be a weighted average of the crash total crash cost or crash frequency of each potential target costs associated with the crash types likely to be affected. section or route. For each intersection or route where Solving for the treatment effectiveness, the equation reads: multiple treatments are possible, the user could compare Ct the crash frequency or total crash cost for each of the dif- Eff = N * Cc ferent possible strategies. Total crash cost will be a much superior criterion if the target crash types being compared The analyst can then determine whether the calculated differ with respect to crash severity. If total crash cost or treatment effectiveness required to reach the breakeven frequency for one treatment strategy clearly exceeds the point is likely to be achievable. total crash cost or frequency for the other, the first would 5. Target the chosen treatments to the intersections where be a logical treatment choice. If the total crash cost or the problem is found. frequency for the different strategies is essentially the