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10 CHAPTER 4 Estimation of Highway Loss This chapter presents the estimated highway loss associ- then divided by the ratio for all persons to provide an adjust- ated with the target groups for which countermeasures have ment factor. For example, if the GES injury/death ratio for been developed. Highway loss can arise from both fatal and pedestrians was 21/1 and the ratio for all groups combined nonfatal injury. Property damage is not considered here was 85/1, then the relative size of the injury/death ratio because it is a relatively small proportion of all loss and is not for pedestrians was 0.25 that of the overall group (i.e., 21/1 consistently reported across the states. 85/1 = 0.25). This proportion (0.25) was then used to adjust the overall injury/death ratio calculated from the Blincoe et al. report (2002). Thus, if the pedestrian injury/death ratio was Target Group Size--Fatal Injury 0.25 of the overall injury/death ratio in the GES data set, The countermeasures reviewed cover differing groups of then it was assumed to be 0.25 the overall injury/death ratio road users and differing numbers of fatal and injury victims. in the data used by Blincoe (126/1). Therefore, multiplying For instance, some involve nonmotorists (pedestrians and 0.25 by 126/1, the overall injury/death ratio from the Blincoe cyclists), others involve alcohol, speed, motorcycles, belt use, dataset resulted in an adjusted 31/1 ratio, which was used teen drivers, etc. The size of each of these target groups varies to estimate costs associated with both deaths and injuries. substantially. Table 1 indicates the number of fatalities asso- Adjusted ratios for various target groups are shown in Table 2. ciated with each of the target groups and the percentage of all Taking pedestrians as an example, the final column in the fatalities that each group represents. table for adjusted ratios was obtained by determining what Note that the groups are not mutually exclusive. For in- proportion of the all persons ratio is comprised of the pedes- stance, a single crash could involve a 16-year-old driver, dis- trian ratio shown in the column for GES ratio relative to all tracted, at night, who had been drinking. persons (hence: 21/85 = 0.25), and adjusting the Blincoe et al. ratio by that factor to provide the data in the last column (125.95 0.25 = 31.49). Target Group Size--Nonfatal Injury The last column of Table 2 indicates the injury/fatality Fatalities are only part, and typically not even the major ratio used to estimate the benefits for each Proven counter- part, of overall highway loss. We estimate, based on Blincoe, measure. Rounding, the first ratio shown is 126/1, which rep- Seay, Zaloshnja et al. (2002), that for every motor-vehicle- resents the overall ratio calculated across all target groups. related fatality, there are 126 associated injuries (of any sever- The next ratio is 31/1 for pedestrians (used in the previous ity). This figure refers to the overall injury-to-fatality ratio example). Based on this procedure, motorcyclists have an (i.e., 126/1). There is substantial variance in this ratio as a injury/fatality ratio of 35/1. Both pedestrians and motor- function of the target population. For instance, motorcyclists cyclists are "unprotected" road users. The result is that these and pedestrians have different injury-to-fatality (i.e., injury/ persons are far more likely to sustain fatal injury, as compared death) ratios than do occupants of passenger vehicles. with a nonfatal injury, given that a crash has occurred. At the To estimate the injury/death ratio for each target group opposite end of the range are child occupants of passenger and then use such ratios to determine target group costs based vehicles. They are highly protected by the car and by the fact on the Blincoe et al. report, this ratio was first calculated for that they are often in the back seat, sometimes in a child re- each target population based on General Estimates System straint device. Their injury/fatality ratio is 656/1, indicating (GES) data for 20042006. The ratio for each subgroup was that fatal injury in the event of a crash is far less likely than