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
Less Fuel
consumption
Better Health Outcome
Statistical Mediation Effects
A
Source(X)
Baron and Kenny's (1986) steps
Mediator
(M)
C
B
Outcome (Y)
Empirical models
1. Y = bX (path C)
𝑙𝑜𝑔𝑖𝑡 𝑎𝑠𝑡ℎ𝑚𝑎 = 𝛼0 + 𝛽1 𝑀𝑃𝐺 + 𝛿𝑍 + 𝜀
2. M ~ aX (path A)
𝐴𝑄𝑆 = 𝛽3 𝑀𝑃𝐺 + 𝑋 + 𝜖
3. Y ~ dM + gX (path A B)
𝑙𝑜𝑔𝑖𝑡 𝑎𝑠𝑡ℎ𝑚𝑎 = 𝛼0 + 𝛼1 𝐴𝑄 + 𝛽2 𝑀𝑃𝐺 + 𝛿𝑍 + 𝜔
g <b
Significant d
Data
Vehicle 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
Average US Light Duty Vehicle Fuel Efficiency
MPG
30.0
20.0
One-the-Road Passenger Cars
10.0
On-the-road Light Trucks
New Passenger Cars
New Light Trucks
0.0
1978
1986
1994
2002
2010
Year
Data source: US DOT NTS
Vehicle Traveled Miles
Averaged Across States
70000
Total
Rural
Urban
Interstate
60000
VMT (Million Miles)
50000
40000
30000
20000
10000
0
1994
1999
2004
Year
2009
2014
Fuel Consumption
Averaged Across States
3600000
3400000
Motor Fuel
Gasoline
Thousand Gallons
3200000
3000000
2800000
2600000
2400000
2200000
2000000
1994
1999
2004
Year
2009
2014
Vehicle Fuel Economy
Averaged Across States, Miles Per Gallon
18
MPG
17
16
15
1994
1999
2004
Year
2009
2014
Pollutant Level - PM 2.5
Averaged Across States
35
PM2.5 98% daily average
PM2.5
30
25
20
15
2000
2002
2004
2006
2008
Year
2010
2012
2014
Econometric models
𝑙𝑜𝑔𝑖𝑡 𝑎𝑠𝑡ℎ𝑚𝑎 = 𝛼0 + 𝛽1 𝑀𝑃𝐺 + 𝛿𝑍 + 𝜀
𝑙𝑜𝑔𝑖𝑡 𝑎𝑠𝑡ℎ𝑚𝑎 = 𝛼0 + 𝛼1 𝐴𝑄 + 𝛽2 𝑀𝑃𝐺 + 𝛿𝑍 + 𝜔
𝐴𝑄𝑆 = 𝛽3 𝑀𝑃𝐺 + 𝑋 + 𝜖
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 Variables
1. BRFSS (individual, 2001 ~2012)
Variable
Health Outcomes
mean
std. dev.
min
median
max
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
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
Demographics
N = 3297711, after data cleaning
2. State level Aggregate
Variable
Health Outcomes
mean
std. dev.
min
median
max
0.0867
0.1020
0.0114
0.0272
0.0527
0.0443
0.0860
0.0998
0.1243
0.1812
PM2.5 - the 98%
27.73
6.768
12.37
27.275
65.5
PM2.5 - Annual Mean
CO - the 2nd highest
CO - the 2nd highest 8-hour average
10.63
3.77
2.22
2.422
2.819
1.521
5.462
0.2
0.3
10.545
3.318
2.05
17.06
33.5
24.3
44.830
14.414
10
43.556
182
22.42
2.903
15.42
22.06
40.97
52.71
0.271
0.191
0.853
0.612
0.883
4.783
3.568
180.9
30.13
3.331
0.058
0.036
0.096
0.027
0.034
0.173
0.240
12.49
1.39
44.331
0.139
0.088
0.431
0.496
0.770
4.178
2.969
164.82
26.57
53.277
0.2771
0.190
0.865
0.611
0.887
4.791
3.558
175.9
30.48
59.509
0.424
0.311
0.982
0.700
0.961
5.336
4.069
217.60
33.12
Has Asthma
Has Diabetes
Air Pollutants
NO2 - the 98%
Average fuel economy (MPG)*
Demographic, State average
Age
Age > 65
Current Smoker
Caucasian
Female
Has Healthcare coverage
Education status
Income level
Weight (lb)
Body Mass Index
N = 490, after data cleaning
From vehicles of surveyee
Model Estimates
1. Pollutants on MPG change (Fixed effects* model)
PM2.5 - the 98%
CO - the 2nd highest
PM2.5 - Annual Mean
1-hour measure
CO - the 2nd highest
8-hour average
NO2 - the 98%
Intercept
29.16
2.22
<.0001
11.06
0.8641
<.0001
0.508
1.003
0.6125
0.618
0.434
0.155
41.47
5.375
<.0001
MPG
-0.35036
0.0975
0.0004
-0.1069
0.0379
0.005
0.104
0.0443
0.0185
0.0346
0.0191
0.0734
-0.632
0.2373
0.0008
GDP
(per Capita)
0.000077
0.000017
<.0001
0.000021
6.73E-06
0.0017
-0.00001
7.82E-06
0.1063
2.24E-06
3.39E-06
0.5078
0.00294
0.000042
<.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
Less air pollutants
More efficient cars
Better Health Outcome
Appendix
Summary Statistics of Data
Summary Statistics
1. Vehicle Miles Traveled Data
Year
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
mean
47,505
48,671
50,203
51,532
52,771
53,918
54,850
55,995
56,684
58,088
58,624
59,100
59,408
58,304
57,976
58,182
57,851
58,224
58,595
std. dev.
49,270
50,066
51,775
52,955
54,397
56,101
56,978
58,644
59,402
61,047
61,546
61,681
62,053
60,966
60,252
60,279
59,898
60,397
61,222
* 51 Observations (States , DC) per year
Unit: Million Miles
min
3,465
3,316
3,326
3,307
3,462
3,498
3,750
3,547
4,150
3,742
3,713
3,623
3,609
3,611
3,608
3,591
3,568
3,572
3,527
median
38,489
38,095
38,840
40,261
41,205
41,771
43,244
43,545
44,156
45,891
47,019
47,742
47,572
47,534
46,230
46,940
46,606
46,889
46,996
max
276,371
278,043
285,612
290,630
300,066
306,649
310,575
320,942
323,592
328,917
329,267
327,478
328,312
327,286
324,486
322,849
320,784
326,272
329,534
Summary Statistics
2. Motor Fuel Consumption Data
Year
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
mean
2,819,294
2,891,194
2,955,141
3,047,163
3,154,183
3,181,879
3,216,655
3,319,333
3,350,931
3,433,397
3,437,278
3,465,700
3,479,611
3,360,889
3,307,774
3,348,558
3,308,266
3,318,093
3,348,023
std. dev.
2,814,409
2,894,570
2,945,592
3,041,332
3,154,373
3,221,068
3,293,103
3,429,090
3,401,700
3,523,439
3,563,084
3,576,027
3,605,670
3,474,344
3,399,097
3,438,297
3,415,528
3,438,667
3,490,113
* 51 Observations (States , DC) per year
min
172,579
160,323
167,905
166,071
167,137
167,175
151,632
151,418
143,447
147,175
150,029
126,845
130,485
110,498
114,024
108,081
95,912
95,566
89,210
Unit: Thousand Miles
median
2,242,018
2,357,797
2,316,542
2,409,446
2,480,228
2,529,568
2,748,231
2,601,286
2,722,406
2,582,305
2,629,394
2,642,087
2,703,810
2,733,263
2,560,726
2,690,581
2,601,608
2,728,070
2,725,960
max
15,211,262
15,511,709
15,874,325
16,213,447
16,777,135
17,080,595
17,460,517
18,297,028
17,795,916
18,647,180
18,860,547
18,711,279
18,842,520
17,829,713
17,450,012
17,464,647
17,233,778
17,118,279
17,287,862
Summary Statistics
3. Fuel Economy Data
Unit: Miles Per Gallon
Year
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
mean
16.48
16.55
16.59
16.60
16.51
16.72
17.07
16.84
16.92
16.78
16.93
17.01
16.99
17.32
17.47
17.34
17.52
17.62
17.71
std. dev.
1.55
1.55
1.61
1.58
1.76
1.74
2.22
1.96
2.30
2.13
2.16
2.42
2.37
2.93
2.86
3.00
3.42
3.45
3.70
* 51 Observations (States , DC) per year
min
12.73
13.04
13.03
12.66
11.42
12.87
12.23
13.45
13.01
11.01
10.89
10.62
11.12
10.72
10.03
10.55
10.15
12.15
12.04
median
16.53
16.62
16.61
16.80
16.41
16.66
16.93
16.73
16.66
16.88
16.73
16.99
16.96
17.39
17.74
17.54
17.61
17.65
17.54
max
20.08
20.68
21.40
20.39
20.85
21.49
24.73
23.54
28.93
25.43
24.75
28.56
27.66
32.68
31.64
33.23
37.20
37.38
39.54
Summary Statistics
4. Air Pollutants (PM2.5) Data
Variable
PM2.5 - the 98% of the daily
average
PM2.5 - the Weighted Annual Mean
Year
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
mean
32.39
30.90
29.86
29.47
31.99
28.19
29.12
25.57
24.06
24.84
24.30
22.07
std. dev.
7.821
8.040
6.219
7.338
6.531
5.161
5.972
4.849
5.212
4.726
4.432
3.396
min
17.25
15.5
18.81
15.5
16
16.62
14.75
15.12
12.37
15.42
15.37
16.5
median
30.90
30.45
29.18
28.58
33
28.25
29.88
25.45
23.44
24.29
24.08
21.58
max
56.71
56
43.5
65.5
43.13
39
49
33.07
37.25
37.25
34.4
29.8
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
12.12
11.40
11.32
11.04
11.94
10.93
11.17
10.19
9.27
9.70
9.49
9.08
2.747
2.635
2.499
2.313
2.782
2.251
2.337
1.903
1.606
1.939
1.744
1.405
6.5
5.76
6.66
5.85
5.76
6.26
6.14
5.88
5.46
5.64
5.46
6.27
12.49
11.43
11.58
11.189
11.81
11
11.04
10.51
9.36
9.61
9.49
9.08
17.06
16.3
15.59
15.04
16.62
15.37
15.68
13.37
12.6
13.54
12.39
11.73
* 49 Observations per Year (48 States and DC)