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73 "weight" the different factors. While problem size (total for safety improvement has been fully committed. The total crash cost) and assumed treatment effectiveness are key fac- benefit of the selected program will not be forecastable, but tors, there may be technical, policy, and cost considerations the success of the program can be determined if a sound eval- that will remove certain treatments from consideration uation is conducted after its implementation. even if they are felt to be effective. The analyst will have to Where quantitative estimates or approximations of effec- choose the final treatments based on best judgment. The tiveness can be made for treatments aimed at distracted or procedure outlined above will at least ensure that the major fatigued drivers, it may be possible to provide estimates of net factors in the decision are clearly defined. The output of this impact (number of crashes prevented) by multiplying the step will be one or more chosen treatments, with the nature unit treatment effects by the number of drivers or roadway of the treatment defining the specific crash types more likely segments treated. Since passenger restraint strategies will not to be affected. The roadway-oriented treatments for drowsy prevent crashes, and because it is difficult to estimate the and distracted drivers (e.g., shoulder and centerline rumble increase in belt use as a result of any specific program or to strips) are also included in the NCHRP Report 500 guides translate that increase into a well-defined reduction in injury discussed in Section IV of this guide and are best addressed severity, providing estimates of net impacts for these treat- with the procedures presented there. ments is more difficult. Seatbelt strategies are most effective 6. Target the chosen treatments to the user populations in communities and among populations where usage rates where the problem is found. are the lowest and there is the greatest room for improve- If targeting is to be done by location, the treatment could ment. And because the proper use of restraint systems is so be targeted to counties, city areas, or routes/streets showing effective at reducing injury level in crashes, it is important to the highest total crash cost or frequency, coupled with the continue to develop and implement effective programs aimed analyst's judgment of potential differences in cost between at increasing restraint use in these communities and among locations and technical and political issues. Mileposted these populations. crash data could be used as discussed in Section III for Procedure 2A to target specific roadways for enforcement Closure related to fatigued drivers. However, for enforcement re- lated to unbelted occupants, targeting of communities Choosing treatments and targeting those treatments to the identified from crash data as having the most crashes unsafe driving populations covered in this section are difficult. involving unbelted occupants (per person, per road mile, or The programs are complex, there is limited crash-based infor- per vehicle-mile of travel) may provide the best targeting mation on treatment effectiveness for the strategies covered in method. Crash data may also be useful in targeting specific the two guides, and there is limited information on program age groups that are being injured as unbelted occupants. costs. However, choices have to be made given that available Targeting information might also be extracted from obser- budgets will always be limited to some degree. Because vational seatbelt use studies done within specific states. programs aimed at these targeted populations are much more focused on driver behavior, they often deal with educational Note again that the lack of treatment effectiveness data and enforcement-related programs more than traditional engi- means that the analyst will not be able to verify whether or neering treatments. The application of these types of programs not a specific set of implemented strategies can be expected to is usually more flexible in nature and costs for implementation meet the established crash-reduction goal. In these cases, the can be more easily adapted to a budget of any size. It is hoped best that can be done is to proceed in selecting strategies and that the procedures presented in this section at least provide target subgroups, times or locations until the available budget some insight into how budgetary choices can be made.