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38 Procedure 3 Choosing Roadway Procedure Treatments and Target Locations When As described in Section III, Procedure 3 has two basic steps: Treatment Effectiveness in Terms of Crash/Injury Reduction Is Not Known · First, choose the best treatments (i.e., the roadway- As noted in the preceding section, the three procedures segment treatments most likely to be applicable in a given described above allow the user to choose roadway-based jurisdiction) from among the set of all roadway-segment treatments and treatment targets for a given problem while treatments presented in the applicable NCHRP Report 500 ensuring that the economic value of the crash/injury reduc- guides. tions will exceed the cost of implementing the program. All · Second, choose the routes or route segments to which the three procedures require that the treatments being examined selected treatments should be applied. each have a known level of effectiveness expressed in terms of an expected crash/injury reduction a defined CRF or AMF. As described earlier in more detail, the choice of the best Unfortunately, many of the roadway-oriented treatments treatments from the listing of many potential roadway-segment and many of the non-roadway-oriented treatments (i.e., treatments can be based on the following factors: driver- and vehicle-oriented strategies) in the NCHRP Report 500 guide series do not have defined levels of effectiveness. a) The potential treatment judged to be the most effective, Thus, economic analyses like those that are the basis for Pro- given that effectiveness is unknown cedures 1, 2A and 2B are not possible for these treatments. b) The relative magnitude of the crash types and severity This Procedure 3 is intended to help the user make an edu- levels that the treatment will affect cated choice of which treatments will be most effective in c) The cost of the potential treatments per mile their jurisdiction, and to help the user develop a targeting d) Other technical or policy considerations strategy for the treatment in cases where it is not to be applied jurisdiction-wide (e.g., where specific routes or route seg- These factors must be combined in some fashion to decide ments are to be targeted). In general, the choice between al- which treatment to choose. While there are multiple ways of ternative roadway-segment treatments will be based on the making this choice, the following represents one such specific nature of the lane-departure crash problem, and the procedure. choice of target locations will be based on the determination of where the crash/injury problem of interest is found. A dis- 1. Prioritize the specific roadway-segment problem(s) to cussion of this more general procedure is included under the be addressed. Procedure 3 subheading in Section III, and the reader should This is related to Factor b in the above list. Here, the review that section. issue is whether to treat run-off-road, head-on, tree-related Procedure 3 is intended for application to tried or experi- or other roadway segment crash types, and on which mental treatments for which the analyst has decided that roadway systems (e.g., two-lane rural roads, four-lane di- there is likely to be a crash/injury reduction benefit, but for vided roads, freeways). This prioritization will be based which the analyst does not have sufficient evidence to esti- on the frequency and severity of the specific types of lane- mate a specific CRF or AMF value. In a case for which the an- departure crashes occurring in a user's jurisdiction. Tar- alyst is able to estimate a specific CRF or AMF value, even if get crash types for each roadway-segment treatment were the estimate is only an approximation, it is recommended defined under Procedure 1. For each crash type, the user that Procedure 4 be used rather than Procedure 3. 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., Data Needs head-on crashes are more severe than run-off-road The only required data for Procedure 3 are crash data that crashes), total crash frequency alone does not provide the will allow the user to specify target crashes for each roadway- complete answer. While an alternative is to restrict the segment treatment under consideration (see Exhibit IV-1 in the analysis to only fatal and serious-injury crashes, this will "crash data" description under Procedure 1). However, in severely limit the crash sample, and will also omit a large order to target the treatment to specific routes or route sections, component of the crash problem non-serious injury the crash data must be "mileposted" or at least contain infor- and no-injury crashes. A better solution is to weight each mation on the county and route. The availability of roadway crash by an economic cost based on its type and severity, inventory data that can be linked to the crash data will improve and then accumulate the total crash cost within each both the treatment choice and the treatment targeting. target crash type. Information on economic cost per
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39 severity level within 22 different crash types including However, for a given set of possible treatments for a par- different types of run-off-road and head-on crashes can ticular crash-type/road-class combination, it may be be found in Crash Cost Estimates by Maximum Police- possible to make a judgment concerning which treatment Reported Injury Severity Within Selected Crash Geometries strategy would be expected to be most effective. For (22). This analysis of total crash cost will provide the user example, for run-off-road crashes on two-lane rural roads, with overall information on which lane-departure crash one would assume that rumble strips on two-lane rural type is most important. roads would be more effective than wider edge lines or The user may further refine this analysis by examining raised delineators. At times, this will clearly be a very dif- crash frequency or total crash cost within roadway classes. ficult judgment to make. If the crash data are mileposted and linkable inventory 4. Choose "best" treatment(s) by considering estimated data are available, details of roadway types can be linked effectiveness, cost per mile and other technical and to each crash record (e.g., number of lanes by divided/ policy considerations. undivided). If inventory data are not available, there may The user will then combine the output of the steps be variables on the crash record itself which can be used in above with at least two other factors in making a final de- a less detailed analysis (e.g., number of lanes, rural vs. cision on which treatment(s) to implement the cost per urban, route type). mile of the treatment and other technical and policy con- This analysis will then produce a listing of potentially siderations. Unfortunately, there are no good guidelines treatable roadway-segment crash types (perhaps by road for how to "weight" the different factors. While problem class) that can be sorted by crash frequency or total crash size (total crash cost) and assumed treatment effectiveness cost, thus providing a ranked listing. For the higher- are key factors, there may be technical, policy, and cost ranked crash types, the user can then conduct additional considerations that will remove certain treatments from analyses to determine more of the specifics of the crash consideration even if they are felt to be effective. The user circumstances (e.g., nighttime vs. daytime distributions of will have to choose the final treatments based on best judg- total crash cost). These additional "drill-down" analyses ment. The procedure outlined above will at least ensure should be designed to provide additional information that that the major factors in the decision are clearly defined. could lead to the choice of one treatment over another The output of this step will be one or more chosen treat- (e.g., raised pavement markers are primarily effective at ments, with the nature of the treatment defining the spe- night or in rainy weather). cific crash types more likely to be affected (e.g., raised de- 2. Identify possible treatments for use for each high-prior- lineators will affect run-off-road crashes at night). ity crash type. The user should be able to work backwards using the The user will then review the pertinent NCHRP Report number of crashes likely to be affected by a given treat- 500 guides and list treatments that would be most appro- ment and the cost of applying that treatment to a given priate for each of the high-priority crash types identified population or location (see items b and c described at the in the above step. The choice should be limited to those beginning of this procedure) to determine the treatment treatment strategies that are classified as tried in the effectiveness needed to maintain a cost-benefit ratio guides. (Proven treatments have known effectiveness lev- greater than or equal to one. els and can be analyzed in one of the three procedures B 1.0 above.) If not already conducted in the "drill-down" Ct analysis in the preceding step, more specific information on the total crash cost related to each potential treatment Where: strategy could be developed by specifying the crash types · B = economic benefit of applying a selected treatment that are most likely to be affected by each strategy (e.g., to a given location or population nighttime run-off-road-right crashes for raised pavement · Ct = the cost of applying that treatment to the selected markers), producing crash frequencies for each specified location or population crash type, and multiplying the frequencies by cost per B = N*Cc*Eff crash. For some strategies, the NCHRP Report 500 guide presents information concerning which crash types are Where: most likely affected by that treatment strategy. · N = Number of target crashes for the subpopulation 3. Rate the possible treatments based on estimated or location where the treatment is to be applied effectiveness. · Cc = average economic cost per target crash Since this procedure deals with treatment strategies · Eff = treatment effectiveness, or the percent reduction with unknown effectiveness, this appears to be impossible. in target crashes