CHAPTER V. POTENTIAL BENEFITS




This chapter estimates the potential benefits of using Hybrid III dummies and incorporating FMVSS 208 head, neck, and chest injury criteria and the corresponding ICPLs. The calculation is based on limited FMVSS 213 sled pulse tests. The agency believes that the proposed seat assembly and crash pulse has a same overall performance as does the current standard. Thus, these changes would not alter the stringency of the compliance test and would likely no benefit impacts.

The chapter is organized into four sections. The first section describes the benefit estimation methodology. The second section estimates the target population represented by each dummy size. The third section presents the fatality and MAIS 2-5 non-fatal injury reduction rates. Finally, the fourth section estimates the potential benefits.




A. Overview of Methodology

The benefit estimation process consists of six steps: (1) identify the target population; (2) estimate the fatality/injury probabilities; (3) calculate the fatality/injury reduction rates; (4) calculate the total weighted fatality/injury reduction rates; (5) calculate the combined head, neck, chest fatality/injury reduction rate; and (6) derive benefits. The following is a detailed description of each step.

Step 1: Identify target population. The FMVSS 213 test is designed to assess child restraint safety in frontal impacts. Therefore, the target population would be all the child passenger vehicle occupant fatalities and injuries in a CRS in frontal crashes. However, the agency believes that the proposed new requirements would have a minimal impact on non-fatal MAIS 1 injuries because the majority of these were skin bruise injuries. Thus, the target population for non-fatal injuries was limited to MAIS 2-5 injuries. In addition, the agency assumes that the new proposal would impact children in a properly used CRS with a MAIS head, neck, or chest injury. As a result, the target population used for the benefit calculation includes the child occupants in a properly used CRS who had a fatal or a MAIS 2-5 head, neck or chest injury. Based on NHTSA's data systems, child restraints were properly used in 82 of 100 fatalities and 1,800 of 1,818 non-fatal MASI 2-5 injuries.

The target population represented by the 12-month-old CRABI is children 1 year old and younger; represented by the 3-year-old dummy is children aged 2 to 3 years old; represented by the 6-year-old dummy is children aged 4 to 6 years old, and represented by the weighted 6-year-old dummy were children aged 7 to 10 years old who weigh less than 66 pounds. The target population is summarized in Table V-1.

Step 2: Estimate the fatality/injury probabilities. For each injury criterion, the corresponding injury probability curves were used to estimate the injury probabilities for each test failing the proposed ICPL. For example, if a dummy measurement was an Nij of 1.5, the child, regardless of child size, would have an 11.7 percent chance of dying from the neck injury and a 31.9 percent chance of receiving a MAIS 2-5 neck injury. The baseline fatal probability for Nij at the proposed level of the standard (i.e., Nij=1), is 6.8 percent and baseline MAIS 2-5 injury probability is 23.0 percent.

Step 3: Calculate the fatality/injury reduction rates. After estimating the injury probability, the reduction rate (r) was calculated for each test failing the ICPL by injury criteria. The reduction has the form: ,

Where p_t = fatality/injury probability at the crash test level,

p_ICPL = fatality/injury probability at the proposed ICPL level.

For example, a CRS test failed at Nij=1.5. The fatality and MAIS 2-5 injury reduction rates for this CRS would be 41.9 [=(11.7-6.8)/11.7] and 27.8 [=(31.9-23.0)/31.9] percent, respectively, after implementing the proposal.

Step 4: Calculate the total weighted reduction rates. For each dummy size, the total weighted fatality and MAIS 2-5 injury reduction rates were calculated separately for each injury criterion, i.e., HIC, neck, chest g, and chest deflection. The total reduction rate was derived using the formula:

r = w _i * r _{i ,} i {1,2,3,...k}

Where

r = the total fatality/injury reduction rate

w _i = the proportion of the specific CRS market share

r _i = the fatality/injury reduction rate from Step 3

k = the number of CRSs failing to meet the specific injury ICPL

The analysis, however, is unable to obtain the market share of each CRS on the market today. The Juvenile Products Manufacturers Association (JPMA) has not been willing to share the information with the agency during the report publication time. The agency believes that the CRSs tested represent those more popular brands on the market, thus, the analysis gives each CRS tested an equal weight, i.e., w _i= 1/n for every i. The number n is the total number of CRS tested within the same dummy group.

Step 5: Calculate the combined head, neck, and chest fatality/injury reduction rate. The combined head, neck, and chest reduction is:

C = w_HIC * r_HIC + w_Nij * r_Nij + w_chest * r_chest - w_HIC * r_HIC * w_Nij * r_Nij - w_HIC * r_HIC * S

w_chest * r_chest - w_Nij * r_Nij * w_chest * r_chest + w_HIC * r_HIC * w_Nij * r_Nij * w_chest * r_chest

Where, w_i is the weight, and


r_i is the total weighted reduction rate from Step 5, for i = HIC, Nij, or Chest.

The weight is the normalized proportion of the injured body region. These weights were derived from the percentage distribution shown in Table II-6. The weights for HIC, Nij, and chest fatalities are 90 percent [=0.71/(0.71+0.01+0.07)] for HIC, 1% for Nij, and 9 percent for chest fatal injury. The corresponding weights for MAIS 2-5 HIC, neck, and chest injuries are: 88 percent [=0.43/(0.43+0.0012+0.06)], 0.2 percent, and 12 percent, respectively. Note that both chest g's and chest deflection predict chest injuries, thus only the maximum of these two reduction rates was used in the combined reduction rate calculation, i.e., r_chest = maximum of (r_{chest g}, r_{chest deflection})

Step 6: Estimate Benefits. The last step is to apply the combined reduction rate derived from Step 5 to the corresponding population to estimate benefits:

B = TP * C

Where, B = benefits (lives that would be saved or MAIS 2-5 injuries that would be reduced

TP= target population of the corresponding test
C= the head, neck, and chest combined reduction rate from Step 5.




B. Target Population

The target population as defined in the methodology section is all the child occupant fatalities and MAIS 2-5 injuries seated in a properly used CRS when a frontal impact occurred. These occupants had a MAIS 2+ head, or neck, or chest injury. Table V-1 (adapted from Table II-7) shows the target child population that would be impacted by the proposed new dummy and injury criteria by age and orientation of CRS. Because the target population is small, the analysis does not segregate the target population further by injured body region.

Annually, there are about 65 fatalities and 891 MAIS 2-5 non-fatal injuries as shown in Table V-1 that could be impacted by the new proposal. The target population represented by the 12-month-old CRABI was children 1 year old and younger. These included 37 infant fatalities and 445 MAIS 2-5 injuries. Represented by the 3-year-old dummy were children aged 2 to 3 including 22 fatalities and 406 MAIS 2-5 injuries. Represented by the 6-year-old dummy were children aged 4 to 6 years old including 5 fatalities and 40 MAIS injuries. Represented by the weighted 6-year-old dummy were children aged 7 to 10 years old with weight less than 66 pounds. This group included only 1 fatality.

Table V-1
Children in Properly Used Child Restraint System (CRS)
With a MAIS 2+ Head, Neck, or Chest Injury

Source: 1999 Fatality Analysis Reporting System; 1999 General Estimated System (GES); 1993-2000 Crashworthiness Data System (CDS)
Note: MAIS 2-5 Injuries were derived from 1993-2000 CDS and adjusted to 1999 GES-CDS equivalent level.

The target population is derived based on the NHTSA collected real-world crash data: the 1999 FARS, 1993-2000 CDS, and 1999 GES. The child fatalities and MAIS 2-5 non-fatal injuries were derived from 1993-2000 CDS and adjusted to 1999 FARS level and 1999 GES CDS-equivalent level, respectively. The 1999 FARS and GES are the most currently available fatality and injury data.




C. Fatality and Injury Reduction Rates

Table V-2 represents the total fatality and MAIS 2-5 non-fatal injury reduction rates by dummy size and injury criteria. The FMVSS 213 pulse sled test data were used to derive these reduction rates. Both chest g's and chest deflection predict the chest injury, thus, only the maximum of these two reduction rates was used to calculate the HIC₁₅/Nij/Chest combined reduction rate. These weights are the normalized proportion of the injury body region as described in the methodology section. For fatalities, the weights are 90 percent [=0.71/(0.71+0.01+0.07)], for HIC₁₅, 1 percent for Nij and 9 percent for chest. For MAIS 2-5 injuries, the corresponding weights are 88 percent [=0.43/(0.43+0.0012+0.06)], 0.2 percent, and 12 percent (the bigger of the chest g's and chest deflection), respectively.

As shown in Table V-2, the highest reduction rates were from reducing neck injury values. However, neck injury carries the least weight in the calculation because of the small target population. The combined head, neck, and chest fatality reduction rates are shown in Table V-2.

Table V-2
Fatality and MAIS Injury Reduction Rates
by Dummy Size and Injury Criteria

Note: unless specified, 0.0% means that all the tests have met the ICPLs
Na - no data available

D. Benefits

The potential benefits are estimated by applying the HIC/Nij/chest combined reduction percentages shown in Table V-2 to the corresponding target population in Table V-1. As shown in Table V-3, the estimated benefits for adapting the FMVSS 208 scaled child injury criteria and corresponding ICPLs would save 3-5 children age 0-1 year old and mitigate 5 MAIS 2-5 injuries in a forward-facing CRS. The proposed amendment also would save 1 child age 4-6 years old and mitigate 1 MAIS 2-5 injuries of the same age group in a booster seat. The estimated benefits reflect the 14 percent of CRS use in fatal frontal crashes and 20 percent in MAIS 2-5 frontal injuries. If more children, especially older children, were restrained in a CRS, the benefits would be higher.

Table V-3
Estimated Fatality and MAIS 2-5 Injury Benefits

* The lower bound was based on the lognormal HIC probability risk curves.