The Health Effects of Automobile Fuel

Economy Standard Through Improving Air

Quality

Qing Shi

UNCG 2015

Background

• Automobile driving has externalities (eg. air population)

• Fuel economy standard - Corporate Average Fuel Economy (CAFE) plays the

primary role in US to regular mobile source pollution

• Health effects of CAFE standard?

Research Questions

• Does fuel economy standard lead to better health outcomes?

• Is there evidence for air pollution as the mechanism (mediator)

• Welfare gain/lost of CAFE

• Policy advice

More fuel efficient cars Less air pollutants Better Health Outcome

Less Fuel consumption

Statistical Mediation Effects

Baron and Kenny's (1986) steps

1. Y = bX (path C)

2. M ~ aX (path A)

3. Y ~ dM + gX (path A B)

g < b

Significant d

Source(X) Outcome (Y)

Mediator(M)A B

C

𝑙𝑜𝑔𝑖𝑡 ( h𝑎𝑠𝑡 𝑚𝑎 )=𝛼0+𝛽1𝑀𝑃𝐺+𝛿 𝑍+𝜀

𝐴𝑄𝑆=𝛽3𝑀𝑃𝐺+𝑋+𝜖

𝑙𝑜𝑔𝑖𝑡 ( h𝑎𝑠𝑡 𝑚𝑎 )=𝛼0+𝛼1 𝐴𝑄+𝛽2𝑀𝑃𝐺+𝛿 𝑍+𝜔

Empirical models

DataVehicle and fuel sales data (US DOT Highway Statistics)

• State level vehicle miles, fuel consumption and derived MPG

• 2001 – 2011, state-year panel

Air Quality System Data (US EPA AQS)

• County level annual average to state level

• PM2.5, Carbon monoxide, Nitrogen dioxide

• 2001 – 2013, state-year panel

Behavioral Risk Factor Surveillance Survey (BRFSS)

• Asthma incidence/status

• 2003 – 2011, state-year pooled cross section

Automobile Fuel Economy improvement

Data source: US DOT NTS

1978 1986 1994 2002 20100.0

10.0

20.0

30.0

Average US Light Duty Vehicle Fuel Efficiency

One-the-Road Passenger Cars

On-the-road Light Trucks

New Passenger Cars

New Light Trucks

Year

MP

G

1994 1999 2004 2009 20140

10000

20000

30000

40000

50000

60000

70000

Vehicle Traveled MilesAveraged Across States

Total Rural Urban Interstate

VM

T (

Mill

ion

Mile

s)

Year

1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 20142000000

2200000

2400000

2600000

2800000

3000000

3200000

3400000

3600000

Motor Fuel Gasoline

Fuel ConsumptionAveraged Across States

Year

Th

ousa

nd

Gal

lon

s

1994 1999 2004 2009 201415

16

17

18

Vehicle Fuel EconomyAveraged Across States, Miles Per Gallon

MP

G

Year

2000 2002 2004 2006 2008 2010 2012 201415

20

25

30

35

PM2.5 98% daily average

Pollutant Level - PM 2.5

Year

PM2.

5

Averaged Across States

Econometric models

𝑙𝑜𝑔𝑖𝑡 ( h𝑎𝑠𝑡 𝑚𝑎 )=𝛼0+𝛽1𝑀𝑃𝐺+𝛿 𝑍+𝜀

𝐴𝑄𝑆=𝛽3𝑀𝑃𝐺+𝑋+𝜖

𝑙𝑜𝑔𝑖𝑡 ( h𝑎𝑠𝑡 𝑚𝑎 )=𝛼0+𝛼1 𝐴𝑄+𝛽2𝑀𝑃𝐺+𝛿 𝑍+𝜔

Empirical Approach

• Run Stepwise logit model select significant Xs, every year

• Run logit regression of Asthma on MPG + X

• Run logit regression of asthma on pollutants and MPG + X

• Run OLS of Pollutants on MPG

Individual Characteristics• Weight

• Body Mass Index – BMI

• BMI Categories – normal, overweight, obese

• Income Level - <15K, 15K – 25K, 25K-35K, 35K=50K, >50K

• Gender, Race

• Smoking status

• Age, Age category - < 65, >=65

• Has healthcare coverage

Summary Statistics of Model Variables1. BRFSS (individual, 2001 ~2012)

N = 3297711, after data cleaning

Variable mean std. dev. min median maxHealth Outcomes          

Has Asthma 0.0879 0.2831 0 0 1

Has COPD 0.0797 0.2708 0 0 1

Has Diabetes 0.1074 0.3097 0 0 1

Demographics          

Age 53.50 17.26 18 54 99

Age > 65 0.284 0.451 0 0 1

Current Smoker 0.184 0.387 0 0 1

Caucasian 0.854 0.353 0 1 1

Female 0.614 0.487 0 1 1

Has Healthcare coverage 0.884 0.320 0 1 1

Education status 4.792 1.080 1 5 6

Income level 3.577 1.463 1 4 5

Weight (lb) 178.8 75.4 0 170 999

Body Mass Index 30.13 14.82 4.78 26.66 99.99

           

2. State level Aggregate

N = 490, after data cleaningFrom vehicles of surveyee

Variable mean std. dev. min median maxHealth Outcomes          

Has Asthma 0.0867 0.0114 0.0527 0.0860 0.1243

Has Diabetes 0.1020 0.0272 0.0443 0.0998 0.1812

Air Pollutants          

PM2.5 - the 98% 27.73 6.768 12.37 27.275 65.5

PM2.5 - Annual Mean 10.63 2.422 5.462 10.545 17.06

CO - the 2nd highest 3.77 2.819 0.2 3.318 33.5

CO - the 2nd highest 8-hour average 2.22 1.521 0.3 2.05 24.3

NO2 - the 98% 44.830 14.414 10 43.556 182

Average fuel economy (MPG)* 22.42 2.903 15.42 22.06 40.97

Demographic, State average          

Age 52.71 3.331 44.331 53.277 59.509

Age > 65 0.271 0.058 0.139 0.2771 0.424

Current Smoker 0.191 0.036 0.088 0.190 0.311

Caucasian 0.853 0.096 0.431 0.865 0.982

Female 0.612 0.027 0.496 0.611 0.700

Has Healthcare coverage 0.883 0.034 0.770 0.887 0.961

Education status 4.783 0.173 4.178 4.791 5.336

Income level 3.568 0.240 2.969 3.558 4.069

Weight (lb) 180.9 12.49 164.82 175.9 217.60

Body Mass Index 30.13 1.39 26.57 30.48 33.12

Model Estimates1. Pollutants on MPG change (Fixed effects* model)

PM2.5 - the 98% PM2.5 - Annual MeanCO - the 2nd highest

1-hour measureCO - the 2nd highest

8-hour average NO2 - the 98%

Intercept 29.162.22<.0001

11.060.8641<.0001

0.5081.0030.6125

0.6180.4340.155

41.475.375<.0001

MPG -0.350360.09750.0004

-0.10690.03790.005

0.1040.04430.0185

0.03460.01910.0734

-0.6320.23730.0008

GDP (per Capita)

0.0000770.000017<.0001

0.0000216.73E-060.0017

-0.000017.82E-060.1063

2.24E-063.39E-060.5078

0.002940.000042<.0001

* From 49 States and DC, 1995 - 2011

Model Estimates

2. Asthma on PM1, PM2, CO1, CO2, NO and MPG,

• Model estimates in 2003, control for demographic characteristics (all sig. at 0.0001)

Conclusion

• Statistically Significant effect of Fuel Economy on Asthma

• Statistically Significant effect of PM2.5 and CO on Asthma

• Statistically Significant effect of Fuel Economy on Air pollutants

• Empirical evidence of the link among

More efficient cars

Less air pollutants

Better Health Outcome

Appendix

Summary Statistics of Data

Summary Statistics1. Vehicle Miles Traveled Data

Year mean std. dev. min median max1995 47,505 49,270 3,465 38,489 276,371

1996 48,671 50,066 3,316 38,095 278,043

1997 50,203 51,775 3,326 38,840 285,612

1998 51,532 52,955 3,307 40,261 290,630

1999 52,771 54,397 3,462 41,205 300,066

2000 53,918 56,101 3,498 41,771 306,649

2001 54,850 56,978 3,750 43,244 310,575

2002 55,995 58,644 3,547 43,545 320,942

2003 56,684 59,402 4,150 44,156 323,592

2004 58,088 61,047 3,742 45,891 328,917

2005 58,624 61,546 3,713 47,019 329,267

2006 59,100 61,681 3,623 47,742 327,478

2007 59,408 62,053 3,609 47,572 328,312

2008 58,304 60,966 3,611 47,534 327,286

2009 57,976 60,252 3,608 46,230 324,486

2010 58,182 60,279 3,591 46,940 322,849

2011 57,851 59,898 3,568 46,606 320,784

2012 58,224 60,397 3,572 46,889 326,272

2013 58,595 61,222 3,527 46,996 329,534

* 51 Observations (States , DC) per year

Unit: Million Miles

Summary Statistics2. Motor Fuel Consumption Data

Year mean std. dev. min median max1995 2,819,294 2,814,409 172,579 2,242,018 15,211,2621996 2,891,194 2,894,570 160,323 2,357,797 15,511,7091997 2,955,141 2,945,592 167,905 2,316,542 15,874,3251998 3,047,163 3,041,332 166,071 2,409,446 16,213,4471999 3,154,183 3,154,373 167,137 2,480,228 16,777,1352000 3,181,879 3,221,068 167,175 2,529,568 17,080,5952001 3,216,655 3,293,103 151,632 2,748,231 17,460,5172002 3,319,333 3,429,090 151,418 2,601,286 18,297,0282003 3,350,931 3,401,700 143,447 2,722,406 17,795,9162004 3,433,397 3,523,439 147,175 2,582,305 18,647,1802005 3,437,278 3,563,084 150,029 2,629,394 18,860,5472006 3,465,700 3,576,027 126,845 2,642,087 18,711,2792007 3,479,611 3,605,670 130,485 2,703,810 18,842,5202008 3,360,889 3,474,344 110,498 2,733,263 17,829,7132009 3,307,774 3,399,097 114,024 2,560,726 17,450,0122010 3,348,558 3,438,297 108,081 2,690,581 17,464,6472011 3,308,266 3,415,528 95,912 2,601,608 17,233,7782012 3,318,093 3,438,667 95,566 2,728,070 17,118,2792013 3,348,023 3,490,113 89,210 2,725,960 17,287,862

* 51 Observations (States , DC) per year

Unit: Thousand Miles

Summary Statistics3. Fuel Economy Data

Year mean std. dev. min median max1995 16.48 1.55 12.73 16.53 20.081996 16.55 1.55 13.04 16.62 20.681997 16.59 1.61 13.03 16.61 21.401998 16.60 1.58 12.66 16.80 20.391999 16.51 1.76 11.42 16.41 20.852000 16.72 1.74 12.87 16.66 21.492001 17.07 2.22 12.23 16.93 24.732002 16.84 1.96 13.45 16.73 23.542003 16.92 2.30 13.01 16.66 28.932004 16.78 2.13 11.01 16.88 25.432005 16.93 2.16 10.89 16.73 24.752006 17.01 2.42 10.62 16.99 28.562007 16.99 2.37 11.12 16.96 27.662008 17.32 2.93 10.72 17.39 32.682009 17.47 2.86 10.03 17.74 31.642010 17.34 3.00 10.55 17.54 33.232011 17.52 3.42 10.15 17.61 37.202012 17.62 3.45 12.15 17.65 37.382013 17.71 3.70 12.04 17.54 39.54

* 51 Observations (States , DC) per year

Unit: Miles Per Gallon

Summary Statistics4. Air Pollutants (PM2.5) Data

* 49 Observations per Year (48 States and DC)

Variable Year mean std. dev. min median maxPM2.5 - the 98% of the daily 2001 32.39 7.821 17.25 30.90 56.71 average  2002 30.90 8.040 15.5 30.45 56

  2003 29.86 6.219 18.81 29.18 43.5  2004 29.47 7.338 15.5 28.58 65.5  2005 31.99 6.531 16 33 43.13  2006 28.19 5.161 16.62 28.25 39  2007 29.12 5.972 14.75 29.88 49  2008 25.57 4.849 15.12 25.45 33.07  2009 24.06 5.212 12.37 23.44 37.25  2010 24.84 4.726 15.42 24.29 37.25  2011 24.30 4.432 15.37 24.08 34.4  2012 22.07 3.396 16.5 21.58 29.8

PM2.5 - the Weighted Annual Mean  2001 12.12 2.747 6.5 12.49 17.06  2002 11.40 2.635 5.76 11.43 16.3  2003 11.32 2.499 6.66 11.58 15.59  2004 11.04 2.313 5.85 11.189 15.04  2005 11.94 2.782 5.76 11.81 16.62  2006 10.93 2.251 6.26 11 15.37  2007 11.17 2.337 6.14 11.04 15.68  2008 10.19 1.903 5.88 10.51 13.37  2009 9.27 1.606 5.46 9.36 12.6  2010 9.70 1.939 5.64 9.61 13.54  2011 9.49 1.744 5.46 9.49 12.39  2012 9.08 1.405 6.27 9.08 11.73