This document discusses the implementation and effectiveness of airbags in reducing highway fatalities. Airbags were introduced in the 1970s but not required until 1998. Over the past 40 years, advancements like airbags, seatbelts, and fuel system standards have increased vehicle safety. A regression model analyzed how factors like year, vehicle miles traveled (VMT), and percentage of vehicles with airbags affected total passenger fatalities from 1975-2014. The regression showed fatalities declining over time as more vehicles were equipped with airbags, though the effect of the airbag percentage was not statistically significant.

1. Airbags – A Milestone Development in Vehicular Safety
George Ly
December 20, 2016
ECON 320
Professor: Scott Farrow

2. 2
Introduction
The paper discusses the implementation of airbags in vehicles and their effectiveness
towards the reduction of highway fatalities. Airbags were introduced into the American
automobile industry in the 1970s as a supplement to seatbelts, but were not required until 1998.
Seatbelts were required in 1967, but only offered so much accident protection (Lives-Saved-
Tech-Timeline). The lap belt was standard, until the introduction of the common and modern,
three point seatbelt, in 1959 (Borroz, 2009). Many automotive companies did not adapt the three
point seatbelt until later on.
Since 1966, there have been significant safety improvements ranging from energy
absorbing steering assemblies, child car seat tethers, fuel system integrity standards, electronic
stability control, and side curtain airbags (Lives-Saved-Tech-Timeline). Some of these
advancements are considered lifesaving technological advancements such as the frontal airbag
and fuel system integrity standards, while others were significant developments.
Over the past 40 years with the establishment of the National Highway Traffic Safety
Administration (NHTSA) and Insurance Institute for Highway Safety (IIHS), there has been
significant advancements in vehicle safety. Not to mention stricter federal safety standards for
vehicles sold in the United States.
This is an important subject, as airbags and restraint systems were initially implemented
to save lives, but were optional. Now they are standard. With a focus on frontal airbags, airbags
have been under scrutiny since their implementation. They have increased costs, made vehicles
heavier and more complex, and recently been the center of massive recalls. So the question is,
have they really reduced highway fatalities since their implementation?

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A model will be created in order to view the effect of the implementation of frontal
airbags. All of the data for vehicle miles is from the Federal Highway Administration (FHWA)
publications Highway Statistics 2014, table VMT-422C, and Highway Statistics, Summary to
1995, table VM-201A. The fatalities information is from the IIHS General Statistics table
“Passenger vehicle occupant deaths vs. all motor vehicle crash deaths, 1975-2014.”
Ambiguities
There are some ambiguities in the dataset that must be addressed prior to the analysis.
Firstly, the data for vehicle miles travelled (VMT) was initially passenger VMT. It excluded
irrelevant vehicle miles like those of commercial vehicles. However, there was a change in data
collection method in 1995, which made it not possible to use passenger VMT. Thus, total VMT
had to be substituted, which was higher than passenger VMT. Essentially, it made the fatalities
per mile slightly smaller than the true value.
Another ambiguity is the age of vehicles in the United States variable. The age of
vehicles in operation (VIO) was calculated from a 2001 study by the National Automobile
Dealers Association (Passenger vehicles in the United States, 2016). It showed the percentage of
the fleet within certain age bins, less than two years, three and six years, seven and ten, and more
than ten years. An ambiguity is the age of the study, as it does not contain the most recent
information. Secondly, there was no specification on vehicles older than 10 years old. An
assumption of 20 years was used for the oldest age. Additionally, there was not a sufficient
amount of data in order to generate an accurate regression model for the percentage of vehicles
equipped with airbags. This had to be done because when the law was enacted, there were still
older, unequipped vehicles on the road. A linear regression was calculated between two points,

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and the equation was used to calculate the percentage of vehicles equipped within that time span.
This was repeated for all four bins. Finally, there was an assumption that only approximately
97% of vehicles will be equipped due to classic cars and modified vehicles unequipped with
airbags. The assumptions taken for this section of the data will have some effect on the
regression model because some numbers were estimated based on official data.
Data Exploration:
Looking at the data, it can be seen that over time passenger vehicle deaths remained
relatively constant from 1975 to 2007. There was a significant drop around 2008, where fatalities
dropped from approximately 30,000 to 20,000. The average for passenger vehicle deaths is
approximately 30,223 and with a standard deviation of ~3968. The relatively large standard
deviation is most likely due to that drop in passenger fatalities in recent years (2008+).
The fatalities per billion miles travelled mean is approximately 14.16, which was
calculated by dividing the fatalities by VMT, which was in million, but converted to billions to
get integers. It had a relatively large standard deviation of 5.08, as it was initially high and then
decreased over time. This shows that the data is relatively dispersed through the dataset, which is
good in this case. The fatalities have been decreasing per billion miles travelled. For the VMT
(millions), is approximately 2.33 million with a large standard deviation of 592,995 also shows
that the data is vastly dispersed. Through time, the VMT has increased as people drove more.
PassengerVehicleDeaths VehicleMiles Millions (All) Fatalities PerMile(Billions)
Mean 30,223.30 Mean 2,334,145.15 Mean 14.16
Standard Deviation 3,968.03 Standard Deviation 592,995.00 Standard Deviation 5.08
Sample Variance 15,745,254.27 Sample Variance 351,643,064,284.59 Sample Variance 25.79
Range 13,924 Range 1,721,363 Range 16.07

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The range and variance also shows how dispersed some of the fields were, as large variances and
ranges are a result of dispersion in the dataset.
Model:
Figure 1. Graph of Fatalities per Billion Miles Travelled
Figure 1 shows the change in the fatalities per billion miles traveled since 1975. The data
was calculated by using the total passenger fatalities divided by the total billion VMT. For
example, 23.05 in year 1975 meant that in every billion miles travelled there were approximately
23 passenger fatalities. Over the past 40 years, the fatalities per billion miles traveled has been
steadily decreasing. There was a significant drop off in the early 1980s, and since 2010 the ratio
has been relatively stable at approximately 7.5. Since 1975, the fatalities per billion miles driven
has dropped significantly, from 23.05 to 6.97 in 2014, a difference of 16.08. Vehicles are
becoming safer each year with new advancements and stricter standards. The fatalities per billion
miles traveled should be expected to drop each year. With the expansion of autonomous vehicles,
y = -0.425x + 861.91
R² = 0.9575
-
5.00
10.00
15.00
20.00
25.00
1975 1980 1985 1990 1995 2000 2005 2010 2015
FatalitiesperBillionMilestraveled
Years
Fatalities Per Billion MIles Traveled (1975 to
2014)

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the ratio may fall greatly. They remove the possibility of driver error in accidents, as they the
vehicle is making the decision. That may or may not reduce the chance of fatality, but remove
some factors.
Figure 2. Regression Line Calculation for Years 6 to 10
Figure 2 shows how the airbags equipped vehicles percentage was calculated. The
midpoints were taken for each of the data bins and the percentage was cumulative. In this graph,
the vehicle ages are within the 6 to 10 years old range. The two points were plotted on the graph
and Excel generated a linear regression. It generated an x-value and y-intercept that was used
calculate the percentage of vehicles in that age range during time, t. “t” was a range years since
airbags were required from 1998. The x-value (slope) was multiplied against t and the y-intercept
was added using the formula y=mx+b. This method was repeated for the other data ranges.
The percentage shows the proportion of vehicles in that year are equipped with airbags.
Even though they were mandated in 1998, there were still vehicles in operation that did not have
airbags equipped. Thus, using the data regarding the age of vehicles in operation helps in
estimating the amount of vehicles that have airbags, by using the age of the fleet. It allows us to
y = 5.575x + 14.213
R² = 1
0
10
20
30
40
50
60
70
0 1 2 3 4 5 6 7 8 9
Percentage
Years
Years 6 to 10

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see if the fatalities changes are due to airbags. As the fleet ages, more vehicles are being
equipped with airbags, as they have been manufactured after 1998. However, there will be a
percentage of vehicles that will not be equipped for various reason, modifications for track
racing, classic vehicles, or imported vehicles. Thus, it is impossible for every vehicle in
operation to be equipped with airbags. Despite that, a majority of the fleet will be equipped with
airbags and they are the ones mostly likely driving on public roads. The proportion not equipped
with airbags does not significantly affect fatalities because they are such a small proportion of
the fleet, and most likely used for purposes off public highways.
Dependent Variable: Total Passenger Fatalities
5% Level of Significance
Variable Coefficient
Intercept 2202283.1374**
(304530.1824)
Year -1110.6353**
(155.6331)
VMT (Millions) 0.0187**
(0.0025)
Airbags Percentage -18.3427
(17.5514)
R – Squared 0.8772
N 40
Figure 3. Regression Table
The regression analysis looks at the variables that affect the total passenger fatalities.
Most of the variables, excluding VMT were all negative. This shows that these variables are
negatively affected the dependent variable over time. The only positive variable, VMT, is very
small at ~0.02. This is slightly increasing the fatalities, which may be due to the ambiguities
discussed early, regarding total VMT used instead of passenger VMT. Also, it may have been

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that VMT has increased. However, a small p-value, less than 0.05, allows concludes that the
variable is significant. Considering that the VMT coefficient is a decimal, converting the
coefficient to 1 requires multiplying it by 50. Since the data is in millions, it would convert to 50
million VMT results in 1 fatality. Considering the ambiguity in the data, it may be slightly less
than 50 million miles, which is a relatively large VMT for 1 fatality. Or it could have been
negative.
For the “year” variable, it has a large negative coefficient. This shows that each year
significantly decreases the fatalities. Each year the fatalities decreases by approximately 1,100.
The p-value is also very small, thus the coefficient is significant at 5%. The coefficient is the
largest out of all of the variables, which shows that the year largely affects fatalities. It appears
that time is a major factor, as many events can occur over a year. New federal regulations for
vehicular safety, roll out and testing of new safety equipment, changing driving habits, along
with public roads built for efficiency and safety can be introduced/implemented yearly. One
possible contributor is the National Traffic and Motor Vehicle Safety Act in 1966, which
mandated uniform safety standards (Branch, 2013). Mandates such as, shatter resistant glass and
seat belts became standard during the next decade. Not to mention, there were changes in the
road safety with the implementation of rumble trips, speed humps, protected left turn lanes, and
guardrail on high speed highways that followed. 1966 was the start of government intervention
in vehicle standards and safety. This ultimately led the way to airbags and other technological
advancements. This would explain the large coefficient for year because of all of the safety
standards that were implemented yearly. Even today, the NHTSA and IIHS perform independent
studies that help improve vehicle safety. Frontal airbags are just one advancement, but road and
other vehicle safety measures were also major components.

9. 9
The airbag variable also decreases the amount of fatalities since their federal requirement
in 1998. Initially, airbags were an option on some vehicles, not a standard. Airbag technologies
have only improved since their introduction with, dual frontal, side curtain, knee, and seat belt
airbags (DeMuro, 2013). Airbags have been credited for saving numerous of lives since their
federal requirement in the United States. Airbags were most effective when combined with
seatbelts, thus when they were simultaneously used, more fatalities were prevented (Haverdink,
2016). The coefficient has a value of -18, with a relatively high p-value of 0.30. Comparing the
p-value at the 5% significance level, it is greater than 0.05, thus it would not be significant.
However, it must be taken into account that values for this variable were calculated through
multiple linear regressions, with a small amount of data. That may have led to the higher p-value.
In the United States, there have been concerns with airbags since the recall of numerous vehicles
that contained Takata branded airbags. They have been known to improperly inflate and send
shrapnel towards occupants, which can lead to serious or fatal injuries (Takata Recall
Expansion). However, they still appear to be reducing fatalities.
The R2 value is relatively high at approximately 0.88, which shows that about 88% of the
variation in the fatalities can be explained by the independent variables, year, VMT, and airbags.
This shows that the regression analysis is a good fit for the data. There was an N=40, which is 40
data points. That helped in creating an accurate regression analysis, as many data points creates a
more accurate fit.

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Conclusion
The data shows that fatalities per billion miles have been steadily decreasing overtime,
and that VMT have increased steadily. Fewer people are dying from traffic related fatalities and
it appears from the regression analysis that airbags are playing a role in this downward trend.
However, time has had the greatest effect on the fatalities. Many things could have happened
over time, as vehicular safety has improved with the addition of new standard technologies like
seatbelt laws, child safety tethers, and rollover curtain airbags. Today, there are even more
standard features including blind spot monitoring, autonomous emergency breaking, and
adaptive cruise control. With the possibility of completely autonomous vehicles in the near
future, which can remove the driver error factor in accidents. Not to mention, there has also been
developments in traffic safety. It has been a combination of the variables that play a role in
reducing the passenger fatalities, as they each reduced the number of fatalities on their own.
Vehicle safety will most likely only improve, it may not be an obscure thought to see near zero
highway fatalities in the future.
Ultimately, it appears that the reduction in fatalities has been due to the intervention of
the government in 1966. It lead the way with safety standards and created a competitive market
for standard safety features. That can be seen today, as car manufacturing are advertising “high-
tech” safety features that are either standard or for entry level vehicles. The frontal airbag
requirement certain has been a significant factor in increasing vehicular safety, and most likely
due to the intervention of the government. Frontal airbags can be contributed to saving lives and
making vehicles safer since their implementation. They are a contributing factor, but the other
federal standards have also contributed to safer vehicles.

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References Page
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seatbelt-turns-50
Branch, A. (2013). National Traffic and Motor Vehicle Safety Act. Retrieved from
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DeMuro, D. (2013, May). Car Safety 101: Different Types of Airbags - Autotrader. Retrieved
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U.S. Federal Highway Administration, Highway Statistics, Summary to 1995 (1997), Table VM-
201A.
U.S. Federal Highway Administration, Highway Statistics 2014 (2016), Table VMT-422C