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Safety Belt Usage and Effectiveness in Reducing Fatalities in

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					    Safety Belt Usage and Effectiveness
           in Reducing Fatalities
      in Passenger Cars with Air Bags

                  Demet Ozkan, D.Sc Candidate

                         Carl E. Nash, Ph.D
FHWA/NHTSA National Crash Analysis Center, The George Washington University
Goal :

To determine safety belt usage and
effectiveness in potentially fatal crashes of
passenger cars and light trucks that have full
front air bags.




                     2
Overview:
Current Methodology – Nash 1998

•   the distribution of fatal crashes according to safety belt usage
    and the potential for being killed as a function of safety belt
    use.

•   the concept of a potentially fatal crash is one where an
    unbelted occupant would be killed, but a belted occupant
    would survive.

•   generalization of the “Double Pair Comparison” method.



                              3
Earlier Studies:
    One of the more widely used is the Double Pair
    Comparison (DPC) method by Evans (1986).
•   Aims to discover how some characteristic affects the occupant’s fatality
    risk.

•   The method focuses on vehicles containing two specific occupants, at
    least one being killed.

•   One as the subject occupant.

•   The other, the control occupant, serves to standardize conditions to
    estimate risk to the subject occupant.



                                   4
Earlier Studies: DPC Method
A Simple Example:

•   The aim: to determine how driver gender influences driver
    fatality risk.

•   The subject occupant: a car driver.

•   The control occupant: a male passenger seated in the right-
    front seat.



                             5
Earlier Studies: DPC Method
Two sets of crashes:
                                           Subject Group   Control Group

The first contains cars with a female driver and
a male passenger, at least one being killed.




The second contains cars with a male driver and
a male passenger, at least one being killed.




                                 6
Earlier Studies: DPC Method
From these crashes the following
quantities are calculated:                 Subject Group   Control Group

A: Number of female drivers killed in cars with
   male passengers

B: Number of male passengers killed in cars with
   female drivers

C: Number of male drivers killed in cars with
   male passengers

D: Number of male passengers killed in cars with
   male drivers


                                   7
Earlier Studies: DPC Method
A: Number of female drivers killed
   in cars with male passengers
                                       Female driver to male passenger
B: Number of male passengers                        ratio:
   killed in cars with female                     r1 = A/B
   drivers


C: Number of male drivers killed
   in cars with male passengers
                                        Male driver to male passenger
D: Number of male passengers                        ratio:
   killed in cars with male drivers               r2 = C/D

                                   8
Earlier Studies: DPC Method
Dividing these two ratios gives :
                   R = r1/r2 = AD/BC


 • Measures the risk of death to a female driver compared with the
 risk of death to a male driver, other factors being essentially the
 same.

 • The crash conditions are effectively standardized because the
 female and male drivers experienced their injuries in a mix of
 crashes that posed similar risks to accompanying male passengers


                              9
Current Methodology: Nash 1998
The Universe of Crashes :

Classification: based on what happens to driver only…

1.   Crashes in which restraint use has no effect because an occupant would survive
     in any case.

2.   Crashes in which restraint use makes the difference between death and survival.

3.   Crashes that are so severe that a driver would not survive even using this
     restraint.

Unit :

…is a passenger car, light truck, or van involved in a crash.
                                     10
  Current Methodology: Classification
         that are restraint
Crashes in which so severe
                                                                          All Drivers who survived                All Drivers who were killed
thatmakes effect because
use has no the difference
     a driver would not
between death and
an occupant would the
survive even using                                                         Survivable
                                                                                                        Survivable
                                                                                                      if Restrained              Not Survivable

survival.
survive in any case.
restraint.
                                                                      Unrestrained           Restrained        Unrestrained            Restrained

                                                       Unrestrained                                              DI        EI              FI        I

                                  Survivable            Restrained                                              DII        EII             FII      II
 Right Front Passengers
      who survived                                      Restrained              No Fatalities                   DIII      EIII            FIII      III

                            Survivable if Restrained   Unrestrained       AIV            BIV         CIV        DIV       EIV             FIV       IV

                                                       Unrestrained        AV               BV       CV         DV         EV              FV       V
 Right Front Passengers
    who were killed             Not Survivable          Restrained        AVI            BVI         CVI        DVI       EVI             FVI       VI

 No Right Front Passenger                                                       No Fatalities                   DVII      EVII            FVII      VII



                                                                            A           B            C           D         E               F
                                                 1                    2                          3
                                                                 11
 Current Methodology: Classification
If a restraint system is more effective,                                All Drivers who survived                All Drivers who were killed
the result will be that some of the
crashes that would have been in                                                                       Survivable
                                                                          Survivable                if Restrained              Not Survivable
column E or F move to column D or C,
respectively.
                                                                     Unrestrained           Restrained       Unrestrained            Restrained

                                                      Unrestrained                                             DI        EI              FI        I

                                 Survivable            Restrained                                             DII        EII             FII      II
Right Front Passengers
     who survived                                      Restrained              No Fatalities                  DIII      EIII            FIII      III

                           Survivable if Restrained   Unrestrained       AIV            BIV        CIV        DIV       EIV             FIV       IV

                                                      Unrestrained       AV                BV      CV         DV         EV              FV       V
Right Front Passengers
   who were killed             Not Survivable          Restrained        AVI            BVI        CVI        DVI       EVI             FVI       VI

No Right Front Passenger                                                       No Fatalities                  DVII      EVII            FVII      VII



                                                                           A           B            C          D         E               F




                                                                12
Traditional Definition of Effectiveness:

                            Rt
      Effectiveness = 1 -             x 100%
                            Ru


Rt = rate of loss or injury for the treated population.
Ru = rate of loss or injury for the untreated population.

  Applies to a situation where we measure a characteristic in
  two randomly parts of a population, one of which is treated
  and one is not.


                            13
Effectiveness:
Based on these…
…we define the effectiveness of the restraint system as:




  In with the full drivers had been
  Or other words, if allsummations: restrained (treated), only those
   in columns C and D would have survived, while if none had been
   restrained, all drivers in columns C, D, E, and F would have died.

                                 14
Effectiveness:
 …Let us define the ratio of restrained to unrestrained occupants within
 the two most serious classes of crashes:

  Where: ά = F/E
         ß = C/D


   If ά = ß we get:

                                      Where:
                                      K = no. of killed drivers
                                      D = total no. of drivers
                                      subscripts indicate belted or unbelted status

                                      This is essentially the Double Pair
                                      Comparison Formula…
                                 15
Current Methodology:
Limitations:
Data used for estimating effectiveness of safety belts comes from
the Fatal Accident Reporting System (FARS).

         Fatalities by Characteristics as Reported in FARS :

                                                                All Drivers who survived          All Drivers who were killed


                                                              Unrestrained       Restrained      Unrestrained      Restrained

                                           Unrestrained                                                                         1

  Right Front Passengers who survived       Restrained         No Fatalities - Not in FARS                                      2

                                           Unrestrained                                                                         3

 Right Front Passengers who were killed     Restrained                                                                          4

                No Right Front Passenger                       No Fatalities - Not in FARS                                      5


                                                                   K                 L                M                 N
                                           A B+C                  D+E                        F
                                                         16
 Current Methodology:
A New Solution to the Effectiveness Problem:

…Let us partition the data in a way that makes use of information about
restraint use:

     i.     u = proportion of drivers who were restrained

     ii.    v = proportion of r.f. passengers who were restrained
            when with an unrestrained driver

     iii.   w = proportion of r.f. passengers who were restrained
            when with a restrained driver


Note: the u’s, v’s and w’s will be different for each set of cells
(uo : survivable, ui : survivable if belted, u : not survivable)

Note: u(1-w) + uw + (1-u)(1-v) + (1-u)v = 1
                                        17
Current Methodology:
 A New Solution to the Effectiveness Problem:                                                                         N1


                                                                   All Drivers who survived                      All Drivers who were killed


                                                                                                      Survivable

                                    L3                              Survivable                      if Restrained            Not Survivable



                                                         Unrestrained               Restrained                Unrestrained            Restrained
                                                                                                       (1-ui)(1-v)      (1-u)(1-v)    u(1-w)
                                         Unrestrained                                                                                              I
                                                                                                       (1-ui)v          (1-u)v        uw
                          Survivable      Restrained                                                                                               II
Right Front Passengers                                                                                 (1-ui)v          (1-u)v        uw
     who survived                         Restrained                   No Fatalities                                                               III
                           Survivable
                                                        (1-uo)(1-v)       uo(1-w)         ui(1-w)      (1-ui)(1-v)      (1-u)(1-v)    u(1-w)
                         if Restrained   Unrestrained                                                                                              IV
                                                        (1-uo)(1-v)       uo(1-w)         ui(1-w)      (1-ui)(1-v)      (1-u)(1-v)    u(1-w)
                                         Unrestrained                                                                                              V
Right Front Passengers       Not
                                                        (1-uo))v          uow             uiw          (1-ui)v          (1-u)v        uw
   who were killed        Survivable      Restrained                                                                                               VI



                                                             A                  B             C              D               E             F


                                                           18
                                                            K                           L                           M                      N
Current Methodology:
A New Solution to the Effectiveness Problem:


                    (1 – ui) N5                 (1 – u) N5
  E =1-                                =1-
                 uM5 + (u – ui) N5               uM5




    …original paper for detailed explanation…


                           19
Data Analysis using Current Methodology:
•   Data for this study comes from the Fatal Accident Reporting
    System (FARS)

•   Accident years 1995 through 2006.

•   The vehicles studied were 1995 and later passenger cars and
    1999 and later light trucks.

•   With few minor exceptions, this includes only vehicles that are
    equipped with both driver and right front passenger air bags.

•   Cases with ambiguous belt use or vehicle identification were
    not included in the study.

                             20
Data Analysis using Current Methodology:
 Results:
 Numbers of 1995-2006 PASSENGER CARS in which people were killed as drivers
 and/or right front passengers.

                  unrestrained        restrained         unrestrained    restrained
   unrestrained                               805       1932      1066      405            I
                                              7394      772        426     3719            II
    restrained        793        8412         1641      171        142     1238           III
                     1985        916          179       429        355      135           IV
   unrestrained      1020        471          116       279        656      249            V
    restrained        408        4325         1069      112        262     2289           VI


                                             20372      11571     6720    18570       no r.f. pass


                       A          B            C         D          E        F




                                                   21
Data Analysis using Current Methodology:
 Results:
 Numbers of 1999-2006 LIGHT TRUCKS in which people were killed as drivers
 and/or right front passengers.

                   unrestrained        restrained     unrestrained           restrained

    unrestrained                               941   1140        95   144                  I
                                              7458   625         52   1142                II
     restrained
                       477        3919        1934   162         21   455                 III
                       870        494          244   295         38    57                 IV
    unrestrained
                       150        85            99   120         41    62                 V
     restrained        82         673          784    66         22   488                 VI

                                              2639   7351       555   4831        no r.f. pass.


                        A          B            C     D          E     F




                                             22
Data Analysis using Current Methodology:
Results     for Passenger Cars:

Belt effectiveness:

•   58 percent for drivers who had a belt use rate of 76 percent.
•   59 percent for right front passengers who had a belt use rate of 75 percent.


Over the 12 years of this study:

•   Safety belts saved a total of 44,000 passenger car front seat occupants, but could
    have saved an additional 19,000 had they been wearing belts.

•   A total of 47,000 died in passenger cars who could not have survived even had
    they been wearing safety belts.

•   Car driver belt use was only 68 percent when they were traveling with no right
    front passenger.
                                     23
Data Analysis using Current Methodology:
Results for Light Trucks:

Belt effectiveness:

•   84 percent for drivers who had a belt use rate of 82 percent.
•   77 percent for right front passengers who had a belt use rate of 79 percent.


Over the 8 years of this study:

•   Safety belts saved a total of 21,000 light front seat occupants, but could have
    saved an additional 11,700 had they been wearing belts.

•   A total of 10,600 died in light trucks who could not have survived even had they
    been wearing safety belts.

•   Light truck driver belt use was only 49 percent when they were traveling with no
    right front passenger.

                                      24
Discussion:
  Comparison:
                                     Effectiveness                      Belt Use Rate

                               Driver       Right Front   Driver with    Driver w/o     Right Front
                                            Passenger     Passenger      Passenger      Passenger

 Passenger     with air bags   58%               59%         76%            72%            75%
   Cars
               w/o air bags    63%               57%         45%            42%            42%

Light Trucks   with air bags   84%               77%         85%            82%            79%
   & Vans
               w/o air bags    81%               71%         49%            48%            42%




Effectiveness
…was not significantly different between vehicles with and without air
bags.


                                            25
Discussion:

•   The high belt use rate is probably a function of the relatively
    young age of the vehicles involved. It is well known that belt
    use in older vehicles, particularly pickups and SUVs, is
    significantly lower than belt use in newer ones.

                                              Effectiveness                      Belt Use Rate

                                        Driver       Right Front   Driver with    Driver w/o     Right Front
                                                     Passenger     Passenger      Passenger      Passenger

          Passenger     with air bags   58%             59%           76%            72%            75%
            Cars
                        w/o air bags    63%             57%           45%            42%            42%

         Light Trucks   with air bags   84%             77%           85%            82%            79%
            & Vans
                        w/o air bags    81%             71%           49%            48%            42%




                                            26
Discussion:
The high belt effectiveness in light trucks is probably due to two factors:

•    the higher proportion of rollovers in these type vehicles where
     safety belts can reduce ejection.

•    the fact that in crashes between light trucks and other vehicles, the
     light truck generally suffers a lower change in velocity (ΔV) and
     less occupant compartment intrusion.
                                           Effectiveness                       Belt Use Rate

                                     Driver        Right Front   Driver with    Driver w/o     Right Front
                                                   Passenger     Passenger      Passenger      Passenger

       Passenger     with air bags   58%              59%           76%            72%            75%
         Cars
                     w/o air bags    63%              57%           45%            42%            42%

      Light Trucks   with air bags   84%              77%           85%            82%            79%
         & Vans
                     w/o air bags    81%              71%           49%            48%            42%


                                              27
      Discussion:
  • These results are consistent with other estimates of belt use and
  effectiveness, and give confidence that belt use is as important in vehicles
  with air bags as in pre-air bag vehicles.
                                                  Effectiveness                      Belt Use Rate

                                            Driver       Right Front   Driver with    Driver w/o     Right Front
                                                         Passenger     Passenger      Passenger      Passenger

             Passenger      with air bags   58%             59%           76%            72%            75%
               Cars
                            w/o air bags    63%             57%           45%            42%            42%
Pre-Airbag




             Light Trucks   with air bags   84%             77%           85%            82%            79%
                & Vans
                            w/o air bags    81%             71%           49%            48%            42%




  • These results do not, however, provide any indication of the
  effectiveness of air bags themselves. However, other studies suggest that
  passenger cars have become safer in the last twenty years despite little
  reduction in rollover fatalities where air bags would provide little or no
  protection.
                                                       28
Discussion:
…results show:
  …that an additional 30,000(total) lives could have been saved
  had all light vehicle occupants been wearing safety belts.

  …the economic consequences of these deaths amounted to
  more than $100 billion.

  …improved safety belt use reminder systems are needed in all
  new vehicles – which would have cost a total of $4 billion
  dollars at $25 per vehicle – as one of the most cost-effective
  means of improving motor vehicle safety even if such systems
  only cut non-use in half.


                           29
Thank you…




   30
 Current Methodology:
              Since we have                                             All Drivers who survived                All Drivers who were killed


              limited knowledge…                                          Survivable
                                                                                                      Survivable
                                                                                                    if Restrained              Not Survivable



                                                                     Unrestrained           Restrained       Unrestrained            Restrained


                                                      Unrestrained                                             DI        EI            FI          I

                                 Survivable            Restrained                                             DII        EII             FII      II
Right Front Passengers
     who survived                                      Restrained              No Fatalities                  DIII      EIII            FIII      III

                           Survivable if Restrained   Unrestrained       AIV            BIV        CIV        DIV       EIV             FIV       IV

                                                      Unrestrained       AV                BV      CV         DV         EV              FV       V

Right Front Passengers
   who were killed             Not Survivable          Restrained      AVI              BVI        CVI        DVI       EVI           FVI         VI


No Right Front Passenger                                                       No Fatalities                  DVII      EVII         FVII         VII



                                                                           A           B            C          D         E               F
                                                                31

				
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