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40 Since different severity levels have different crash costs, the sideration are characterized by different target crash types value used for Cc can be a weighted average of the crash (e.g., tree-related crashes vs. total run-off-road crashes), and costs associated with the crash types likely to be affected. if the crash data are mileposted or include route informa- Solving for the treatment effectiveness, the equation reads: tion, the user could use the outputs of Step 5 above in mak- ing the targeting decision. Step 5 produced total crash cost Ct or crash frequency of each potential target section or route. Eff = N * Cc For each segment or route where multiple treatments are possible, the user could compare the crash frequency or total The analyst can then determine whether the calculated crash cost for each of the different possible strategies. Total treatment effectiveness required to reach the breakeven crash cost will be a much superior criterion if the target crash point is likely to be achievable. types being compared differ with respect to crash severity. If 5. Target the chosen treatments to the roadway segments total crash cost or frequency for one treatment strategy where the problem is found. clearly exceeds total crash cost or frequency for the other, the Since this procedure concerns treatment strategies first would be a logical treatment choice. If the total crash without known effectiveness, it will not be possible to tar- cost or frequency for the different strategies is essentially the get the treatments based on any type of economic analysis same, the user will need to make the decision based on "best such as those in Procedures 1, 2A and 2B. Instead, the judgment" (e.g., which treatment is being used on adjacent treatment will be targeted to roadway segments or routes roadway segments). showing the highest total crash cost or frequency, coupled 7. Add new treatments, new targets, or new approaches with user judgment concerning the nature of the roadway (e.g., inclusion of safety treatments in normal mainte- and roadside at potential target locations and technical nance or rehabilitation efforts) until the available fund- and political issues. If the crash data are mileposted, the ing is used. user could (1) link crashes to routes and search for the lo- In Procedures 1, 2A and 2B, an iterative process is used cations of "clusters" of target crashes for possible treat- until sufficient treatment types and locations are selected ment, or (2) use a network screening program similar to such that the established crash reduction goal can be that described under Procedure 2A to identify 1-mile sec- reached. In Procedure 3, without effectiveness measures tions with the highest crash frequency or crash burden (by for the treatments, it is not possible to verify whether or weighting each crash by its economic cost and summing not a specific set of treatment types and treatments will total crash cost within each window). The windows iden- meet the established goal. Therefore, the best that can be tified by the network screening program could then be done is to proceed in selecting treatments types and treat- ranked by frequency or total crash cost to identify priority ments until the available budget for safety improvement locations. The user would then correct for "treatment has been fully committed. The total benefit of the selected gaps" using the same logic provided in Procedure 2A. program will not be forecastable, but the success of the If the crashes are not mileposted, but there is informa- program can be determined by evaluations conducted tion available on jurisdiction and route, the user could link after its implementation. 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 Procedure 4 Choosing Treatments crashes on that route by route length. The user can then and Target Populations in Emphasis rank the potential routes for treatment based on this rate Areas for which Some Candidate per mile, and choose the routes to be treated based on the Treatments Have Known Effectiveness highest rankings plus other technical and policy factors. Estimates and Other Treatments Do Not 6. Decide what to do with multiple treatments on the same segments/routes. In many situations, users considering a safety improvement The above steps could possibly produce roadway loca- program in a particular emphasis area will need to consider tions or routes within a jurisdiction that could be treated both treatments that have known effectiveness measures and with multiple treatments. Unlike the earlier procedures treatments that do not. In this situation, it is recommended where it was possible to estimate combined effectiveness for that the user give priority to treatments that have known multiple treatments on the same segments or routes, since effectiveness measures (proven treatments). Treatments that treatment effectiveness is not known here, the user will have have been used extensively but for which effectiveness meas- to use other factors in the final treatment choice for these lo- ures are not available (tried treatments) should then be cations. If the potential treatment strategies still under con- considered. Experimental treatments may have a modest role

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41 in a safety improvement program, particularly if the program mates are realistic. This estimation was not suggested in is structured to evaluate the effectiveness of the experimental Procedure 3 for this reason. It is only suggested at this procedure. point since the user has already considered all proven The recommended planning approach in this situation is a treatments before reaching this stage. It is suggested that hybrid of Procedures 1, 2A, 2B, and 3 described above. 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 Procedure by more than 15 to 25 percent. 1. Determine if proven treatments can meet the established b) When possible, formulate an effectiveness estimate goal. that is applicable to particular target crash types Consider treatments with known effectiveness meas- only, not to total crashes. ures (proven treatments) using either Procedure 1, 2A, or c) Base estimates for tried treatments on CRFs for sim- 2B as appropriate, depending on the types of data avail- ilar treatments if they exist. For example, a CRF ex- able. Determine the crash/injury reduction achieved and ists for shoulder rumble strips. Other treatments compare it to the established crash/injury reduction goal. that also try to keep the driver from leaving the If the goal has not yet been met, proceed to Step 2. roadway by alerting him (e.g., enhanced edgeline 2. Consider tried treatments to supplement the proven ones. marking, raised profile marking) but do not give the This step would involve consideration of treatments with- same level of warning would be expected to have out known effectiveness that have been used extensively by somewhat similar, but lower, CRFs. highway or driver/vehicle agencies (tried treatments). If it is Once effectiveness is estimated, apply Procedure 1, 2A or 2B possible to estimate the effectiveness of these treatments as appropriate, depending on the types of data available. based on imperfect information, then proceed to Step 3; Determine the crash/injury reduction achieved in Steps 1 otherwise, proceed to Step 4. and 3 combined and compare it to the established crash/ 3. Estimate the effectiveness of tried treatments if possible, injury reduction goal. If the goal has not yet been met, and analyze them using the appropriate procedure proceed to Step 4. above. 4. Consider additional tried treatments. This step involves attempting to estimate the effective- For treatments for which reliable effectiveness measures ness of treatments without known CRFs or AMFs. Note cannot be estimated in Step 3, apply Procedure 3 to select that estimating treatment effectiveness is very difficult additional treatment types and target locations until all and can lead to poor treatment choices unless the esti- available funds have been budgeted.