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5, and this step may be skipped. If the analyst has used in- treatment, and the effectiveness of the third treatment
dividual crash types (or crash types by severity and speed applied to the same driver subgroup be reduced to
limit) in the above steps, those individual estimates 25 percent of the original level. (Assume that any addi-
within each subgroup must be summed to calculate the tional treatments after the third will have no additional
total economic benefit for each subgroup. effect.) For example, assume that the first treatment for a
7. Define the annual cost for treating all drivers in each given AR subgroup has an effectiveness level of 20 per-
subgroup. cent, the second has an effectiveness level of 15 percent,
This will be an estimate of total program cost for and the third has an effectiveness level of 10 percent. The
each treatment under study and for each subgroup being estimated combined effectiveness of the three treatments
considered. This assessment will require subjective ap- applied to the same segment would be 20% + 15% (.5) +
proximations. Some general information on treatment 10% (.25) = 30%. Again, this is only an estimate of the
cost is presented for each treatment in the guide, and that true combined effectiveness at best.
information should be reviewed by the user. Depending
on the treatment, this cost may include start-up cost and
Alternative Procedure Choosing
cost per driver (i.e., all drivers that would need to be
Treatments and Target Subgroups
treated without knowing who will subsequently be in-
for Alcohol-Related Crash Strategies Based
volved in an AR crash). For other treatments, this may
On Existing DWI Program Needs
simply be an annual cost (e.g., for public information
programs). Note that the total cost over the expected life The above two procedures for choosing treatments and
of the project will need to be amortized to an "annual subgroups have been based on the size of the alcohol-related
cost" basis, since the benefit calculations are in annual crash problem among different target subgroups of drivers
numbers [see NCHRP Report 501 (18)]. and, in the second procedure, on estimated treatment effec-
8. Calculate "net benefits" for each treatment by tiveness. Both are based on crash data, which make them the
subtracting cost from benefits. recommended procedures to follow. However, in the absence
9. Choose the treatments (and thus treatment subgroups) of crash data, a third alternative procedure that is advocated
with the greatest net benefit. in Volume 1, the AR Guide, is to conduct a careful assessment
10. Decide whether to use multiple treatments. of the nature of the jurisdiction's drinking-driving problem and
After reviewing the prioritized listing of treatments how the DWI countermeasure system is currently functioning.
and estimated costs, the analyst may decide to further de- The choice of AR treatment strategies from those listed in the
termine whether multiple treatments would be beneficial. guide (and thus the choice of target subgroups) would be
If the treatment combinations being considered affect dif- based primarily on "current AR program needs" strategies
ferent driver subgroups (e.g., one affects young AR driv- that are not currently being implemented, or whose imple-
ers while the second affects [older] multiple offenders), mentation can be significantly improved. This assessment of
then the net benefit of that combination will be the sum current program needs requires a multidisciplinary team,
of the individual calculations from Step 8. However, this since the system for dealing with alcohol-impaired driving
is not usually the case. Multiple treatment combinations may be the most complex and involve the greatest number of
will often affect the same subgroup even if they are aimed disciplines and state agencies of any traffic safety issue. States
at different subgroups. In this case, Steps 28 will need to frequently use a task force that represents all the key elements
be repeated for each combination under study. Thus the of this system. Without such an approach, a fragmented and
potentially affected driver groups will be specified first, incomplete understanding of the problem is likely and
then the AR crashes will be calculated, etc. progress will be difficult.
Note, however, that one cannot expect that two treat- The National Highway Traffic Safety Administration
ments with estimated levels of effectiveness A% and B% (NHTSA) works with highway safety offices within states to
will produce a reduction of A% + B% if applied to the facilitate such an assessment procedure using outside experts.
same driver group. The combined effect would be ex- A brief description of NHTSA's program assessment process
pected to be less. Unfortunately, since we do not have can be found at http://www.nhtsa.dot.gov. A more detailed
good data on the effectiveness of individual treatments, description of this process for impaired driving and recent
we have even less knowledge about the effectiveness of findings from such assessments can be found at http://www.
combined treatments. In the absence of such knowledge, nhtsa.dot.gov/cars/rules/regrev/evaluate/809815/index.html.
it is suggested that the effectiveness level of the second Finally, it is strongly recommended that the findings of an
treatment applied to a given driver subgroup be reduced assessment of program needs be combined with crash-based
to 50 percent of the level originally estimated for that information on the size of the AR problem attributable to
