Appendix D 

Health Impacts from On-Road Diesel Vehicles 

D-1 

Assessment of Health Impacts from On-Road Diesel Vehicles 

A. Methodology 

Details on the methodology used to calculate these estimates can be found in Appendix 

A of the Emission Reduction Plan for Ports and Goods Movement in California 

(CARB, 2006). 

1. Primary Diesel PM 

As part of the development of emission reduction plans and control measures for 

particulate matter, including that for ports and goods movement, the California Air 

Resources Board quantifies some of the health impacts of exposure to current and 

future levels of ambient PM. The estimation of premature death and other health 

impacts from PM exposure used by CARB staff is based on a peer-reviewed 

methodology developed by the U.S. Environmental Protection Agency for their risk 

assessments (US EPA, 1999, 2004, 2005). This methodology is regularly updated by 

CARB staff as new epidemiological studies and other related studies are published that 

are relevant to California’s health impacts analysis. The methodology uses 

concentration-response functions which describe the relation between exposure to 

ambient PM2.5 concentration and premature death and illness. The selection of the 

concentration-response functions was based on the latest epidemiologic literature, as 

described in Emission Reduction Plan for Ports and Goods Movement in California 

(CARB, 2006) and Methodology for Estimating the Premature Deaths Associated with 

Long-term Exposure to Fine Airborne Particulate Matter in California (CARB, 2008). 

The central estimate of the relative risk of premature death used in this assessment is a 

10% per 10 μg/m3

 increase in PM2.5 exposures, with a confidence interval of 3% - 20% 

(CARB, 2008). 

For this analysis, staff used a “tons per incident” approach to estimate the health 

impacts associated with emissions from the on-road trucks and buses. Using the 

estimated diesel PM concentration for year 2005 (1.6 μg/m3), the diesel PM2.5 

emissions for year 2005 (37,800 tons), and the concentration-response functions for 

mortality and morbidity (CARB 2006, 2008), we estimated the number of tons per year 

of primary diesel PM that can be associated with each case of health endpoint for the 

year 2005 in California. 

For example, using this information for premature mortality, we estimate that for a 

reduction of 10.8 tons diesel PM2.5 emissions per year, one fewer premature death 

would result. This factor is derived by first determining the total number of premature 

deaths from exposure to 1.6 μg/m3

 of diesel PM2.5, which was estimated to be 3,500 

per year. Then the total annual diesel PM2.5 inventory (37,800 tons) is divided by 

3,500 premature deaths to calculate the factor of tons per premature death. Although a 

single statewide factor (tons per case of health endpoint) is discussed in this example, 

staff actually developed basin-specific factors for the health impacts assessment of 

emissions from on-road trucks and buses. These basin-specific factors were developed 
D-2 

using basin-specific diesel PM concentrations and emissions for the year 2005. The 

basin-specific factors were applied to each air basin to estimate health impacts. 

a. Health Impacts of Diesel PM Baseline Emissions 

After adjusting for population changes, staff estimates that baseline PM emissions from 

in-use on-road diesel vehicles in the years 2010 to 2025 are associated with 

approximately 1100 annual premature deaths (330 – 2000, 95% CI). Estimates of other 

health impacts, such as hospitalizations and asthma symptoms, were calculated using 

basin-specific factors developed from other health studies, basin-specific diesel PM 

concentrations, and emissions. Details for these estimates can be found in Appendix A 

of the Emission Reduction Plan for Ports and Goods Movement in California (ARB, 

2006). 

b. Benefits of Diesel PM Emissions Reductions 

After adjusting for population changes between each future year and 2005, staff 

estimates that the cumulative total of approximately 34,600 tons of PM2.5 emissions 

from on-road trucks reduced through implementation of this regulation in years 2010 – 

2025 are associated with a reduction of approximately 3,300 deaths (990 – 6,000, 95% 

CI). Estimates of other health benefits, such as hospitalizations and asthma symptoms, 

were calculated using basin-specific factors developed from other health studies. 

2. Secondary Diesel PM 

In addition to directly emitted PM, diesel exhaust contains NOx, which is a precursor to 

nitrates, a secondary diesel-related PM formed in the atmosphere that can lead to 

additional health impacts beyond those associated with directly emitted diesel PM2.5. 

To quantify such impacts, staff developed population-weighted nitrate concentrations for 

each air basin using data not only from the statewide routine monitoring network, which 

was used in Lloyd and Cackette (2001), but also from special monitoring programs such 

as IMPROVE and Children’s Health Study (CHS) in years 2004, 2005 and 2006. The 

IMPROVE network provided additional information in the rural areas, while the CHS 

added more data to southern California. Staff calculated the health impacts resulting 

from the three-year average exposure to these concentrations of PM2.5 and then 

associated the impacts with the basin-specific NOx emissions from diesel sources to 

develop basin-specific factors (tons per incident). The basin-specific factors and 

emissions were applied to each air basin to estimate health impacts. Other health 

effects were also estimated as outlined above. 

Using an approach similar to that used for primary diesel PM and adjusting for 

population changes between each future year and 2005, staff estimates that the 

cumulative reduction of approximately 480,000 tons of NOx emissions from the 

implementation of the on-road truck rule from 2010 to 2025 are associated with the 

reduction of an estimated 6,100 premature deaths (1,800 – 11,000, 95% CI). Other 

health effects were also estimated as outlined above. 
D-3 

3. Assumptions and Limitations of Health Impacts Assessment 

There are a number of uncertainties involved in quantitatively estimating the health 

impacts associated with exposure to outdoor air pollution. They include the selection 

and applicability of the concentration-response functions, the exposure assessment, 

and the baseline incidence rates. These are briefly described below. 

• A primary uncertainty is the choice of the specific studies and the associated 

concentration-response (C-R) functions used for quantification. Epidemiological 

studies used in this report have undergone extensive peer review and include 

sophisticated statistical models that account for the confounding effects of other 

pollutants, meteorology, and other factors. While there may be questions on 

whether C-R functions from the epidemiological studies are applicable to California, 

it should be noted that some of the cities in the ACS cohort are in California. Also, 

studies have shown that the mortality effects of PM in California are fairly consistent 

with those found in other locations in the United States (Dominici et al. 2005, 

Franklin et al. 2007, Jerrett et al. 2005; Pope et al. 2002). The C-R function for 

PM2.5-related mortality used in this report was based on a careful review of all 

relevant scientific literature and a thorough consideration of each study’s strengths 

and limitations. In addition, it was approved by our advisors and independent peer 

reviewers. 

• In this assessment, staff assumed diesel PM is as toxic as ambient PM2.5. 

However, this approach may underestimate the true effects of diesel PM exposure 

on adverse health outcomes. Indirect evidence for this possibility comes from a 

number of studies that link motor vehicle-related PM exposure to premature death 

including: Elderly people living near major roads had almost twice the risk of dying 

from cardiopulmonary causes (Hoek et al., 2000); PM from motor vehicles was 

linked to increased mortality (Tsai et al., 2000); PM2.5 from mobile sources 

accounted for three times the mortality as did PM2.5 from coal combustion sources 

(Laden et al., 2000). 

• This report estimated health impacts due to emissions. The methodology applies a 

“tons per incident” factor to estimate the number of health effects associated with 

PM2.5 emissions and assumes the emissions are evenly distributed within the air 

basin. 

• CARB staff assumed the baseline incidence rate for each health endpoint was 

uniform across each county. This assumption is consistent with methods used by 

the U.S. EPA for its regulatory impact assessment, and the incidence rates match 

those used by U.S. EPA. 

• Although the analysis illustrates that diesel PM exposure would be associated with 

health effects to people living in California, we did not provide estimates for all 

endpoints for which there are C-R functions available. Health effects such as 

myocardial infarction (heart attack), chronic bronchitis, and onset of asthma were 

unquantified due to the potential overlap with the quantified effects such as lower 
D-4 

respiratory symptoms and hospitalizations. In addition, estimates of the effects of 

PM on low birth weight and reduced lung function growth in children are not 

presented. While these endpoints are significant in an assessment of the public 

health impacts of diesel exhaust emissions, there are currently few published 

investigations on these topics, and the results of the available studies are not 

entirely consistent (CARB, 2006). In summary, because only a subset of the total 

number of health outcomes is considered here, the estimates should be considered 

an underestimate of the total public health impact of diesel PM exposure. 

B. Health Impacts Associated with Baseline Diesel PM Emissions 

Staff estimates that approximately 4,500 premature deaths (1,400 – 8,000, 95 percent 

confidence interval (95% CI)) are associated with the baseline uncontrolled emissions 

from on-road trucks and buses in the year 2008. Other health impacts are listed in the 

Table 1. The methodology for estimating these health impacts is outlined below. 

Details can be found in Appendix A of the Emission Reduction Plan for Ports and Goods 

Movement in California (CARB, 2006). 

Compared to the estimate for truck emissions presented in the CARB 2006 report, the 

health impacts presented here differ due to the following reasons: 

1) The concentration-response function relating changes in long-term PM2.5 

exposure to risk for premature death was updated from Pope et al. 2002 to 

CARB (2008); 

2) The category of “trucks” was expanded to include medium heavy duty trucks or 

buses; 

3) Emissions were estimated based on EMFAC2007; 

4) Spatial allocation was updated to reflect real-world variation in emissions 

throughout California. 

In short, the current estimated emissions and the associated health impacts presented 

in this report are the most up-to-date and reflect the most current understanding on the 

subject matter. 
D-5 

Table 1: Baseline Health Impacts Associated With Emission from 

On-Road Trucks and Buses for year 2008* 

Endpoint 

 

Pollutant

 

# of Cases 

95% C.I. 

(Lower Bound)

# of Cases 

(Mean) 

# of Cases 

95% C.I. (Upper 

Bound) 

PM 330 1,100 2,000 

Premature Death NOx 1,000 3,400 6,000 

Total 1,400 4,500 8,000 

PM 8 21 35 

NOx 320 560 830 

Hospital admissions 

(Respiratory) 

Total 330 590 860 

PM 47 90 130 

NOx 330 530 780 

Hospital admissions 

(Cardiovascular) 

Total 380 620 910 

PM 6,900 18,000 28,000 

NOx 21,000 53,000 83,000 

Asthma & Lower 

Respiratory 

Symptoms Total 28,000 71,000 110,000 

PM 0 1,500 3,200 

Acute Bronchitis NOx 0 4,200 8,700 

Total 0 5,700 12,000 

PM 93,000 110,000 130,000 

Work Loss Days NOx 290,000 340,000 390,000 

Total 380,000 450,000 520,000 

PM 520,000 640,000 760,000 

NOx 1,600,000 2,000,000 2,300,000 Minor Restricted 

Activity Days 

Total 2,100,000 2,600,000 3,100,000 

* Health effects from primary and secondary PM are labeled PM and NOx, respectively. The sum of PM 

and NOx impacts may not equal the total given due to rounding. Estimates for premature deaths are 

based on an updated relative risk of 10% per 10 μg/m

3 change in long-term PM2.5 exposure, with a 

confidence interval of 3% - 20% (CARB, 2008). 

C. Health Benefits of Reduction in Emissions from In-Use Off-Road Vehicles 

A substantial number of epidemiologic studies have found a strong association between 

exposure to ambient PM2.5 and a number of adverse health effects (CARB, 2002). For 

this report, ARB staff quantified seven noncancer health impacts associated with the 

change in exposures to the diesel PM emissions. This analysis shows the statewide 

cumulative health impacts of the emissions reduced through this regulation from year 

2010 through 2025. Staff estimates that the cumulative emissions reductions would 

result in approximately 9,400 fewer premature deaths. Other health impacts are listed 

below in Table 2. 
D-6 

The impacts associated with primary PM and secondary PM diesel emissions are listed 

separately. The methodology for estimating these health impacts is outlined above and 

details can be found in Appendix A of the Emission Reduction Plan for Ports and Goods 

Movement in California (CARB, 2006). 

Table 2: Total Health Benefits Associated with Reductions in Emissions from the

Implementation of the On-Road Truck and Bus Regulation 

(2010-2025)* 

Endpoint 

 

Pollutant 

# of Cases 

95% C.I. (Lower 

Bound) 

# of Cases 

(Mean) 

# of Cases 

95% C.I. (Upper 

Bound) 

PM 990 3,300 6,000

Premature Death NOx 1,800 6,100 11,000

Total 2,800 9,400 17,000

PM 23 64 110

NOx 580 1,000 1,500

Hospital admissions 

(Respiratory) 

Total 600 1,100 1,600

PM 140 270 400

NOx 590 960 1,400

Hospital admissions 

(Cardiovascular) 

Total 730 1,200 1,800

PM 20,000 53,000 85,000

NOx 39,000 96,000 150,000

Asthma & Lower 

Respiratory 

Symptoms Total 59,000 150,000 230,000

PM 0 4,400 9,600

Acute Bronchitis NOx 0 7,600 16,000

Total 0 12,000 25,000

PM 280,000 330,000 380,000

Work Loss Days NOx 520,000 620,000 710,000

Total 800,000 950,000 1,100,000

PM 1,600,000 1,900,000 2,300,000

NOx 2,900,000 3,600,000 4,200,000 Minor Restricted 

Activity Days 

Total 4,500,000 5,500,000 6,500,000

* Health effects from primary and secondary PM are labeled PM and NOx, respectively. The sum of PM 

and NOx impacts may not equal the total given due to rounding. Estimates for premature deaths are 

based on an updated relative risk of 10% per 10 μg/m

3 change in long-term PM2.5 exposure, with a 

confidence interval of 3% - 20% (CARB, 2008). 
D-7 

D. Economic Valuation of Health Effects 

This section describes the methodology for monetizing the value of avoiding adverse 

health impacts. 

The U.S. EPA has established $4.8 million in 1990 dollars at the 1990 income level as 

the mean value of avoiding one premature death (U.S. EPA, 1999). This value is the 

mean estimate from five contingent valuation studies and 17 wage-risk studies. 

Contingent valuation and wage-risk studies examine the willingness to pay (or accept 

payment) for a minor decrease (or increase) in the risk of premature death. For 

example, if individuals are willing to pay $800 to reduce their risk of mortality by 

1/10,000, then collectively they are willing to pay $8 million to avoid one death. This is 

also known as the “value of a statistical life” or VSL.1

As real income increases, people are willing to pay more to prevent premature death. 

U.S. EPA adjusts the 1990 value of avoiding a premature death by a factor of 1.2012 to 

account for real income growth from 1990 through 2020, (U.S. EPA, 2004). Assuming 

that real income grows at a constant rate from 1990 until 2030, we adjusted VSL for real 

income growth, increasing it at a rate of approximately 0.6% per year. We also updated 

the value to 2007 dollars. After these adjustments, the value of avoiding one premature 

death is $8.9 million in 2007, $9.2 million in 2010 and $10 million in 2025, all expressed 

in 2007 dollars. 

The U.S. EPA also uses the willingness-to-pay (WTP) methodology for some non-fatal 

health endpoints, including lower respiratory symptoms, acute bronchitis and minor 

restricted activity days. WTP values for these minor illnesses are also adjusted for 

anticipated income growth through 2025, although at a lower rate (about 0.2% per year 

in lieu of 0.6% per year). 

For work-loss days, the U.S. EPA uses an estimate of an individual’s lost wages, (U.S. 

EPA, 2004), which CARB adjusts for projected real income growth, at a rate of 

approximately 1.5% per year. 

“The Economic Value of Respiratory and Cardiovascular Hospitalizations,” (CARB, 

2003), calculated the cost of both respiratory and cardiovascular hospital admissions in 

California as the cost of illness (COI) plus associated costs such as loss of time for 

work, recreation and household production. When adjusting these COI values for 

inflation, CARB uses the Consumer Price Index (CPI) for medical care rather than the 

CPI for all items. 

 

1

 U.S. EPA’s most recent regulatory impact analyses, (U.S. EPA 2004, 2005), apply a different VSL 

estimate ($5.5 million in 1999 dollars, with a 95 percent confidence interval between $1 million and $10 

million). This revised value is based on more recent meta-analytical literature, and has not been endorsed 

by the Environmental Economics Advisory Committee (EEAC) of U.S. EPA’s Science Advisory Board 

(SAB). Until U.S. EPA’s SAB endorses a revised estimate, CARB staff continues to use the last VSL 

estimate endorsed by the SAB, i.e., $4.8 million in 1990 dollars. 

2

 U.S. EPA’s real income growth adjustment factor for premature death incorporates an elasticity estimate 

of 0.4. 
D-8 

Table 3 lists the valuation of avoiding various health effects, compiled from CARB and 

U.S. EPA publications, updated to 2007 dollars. The valuations based on WTP, as well 

as those based on wages, are adjusted for anticipated growth in real income. 

Benefits from the proposed rule for on-road trucks are substantial. CARB staff 

estimates cumulative benefits over the period from 2010 to 2025 to be $69 billion using 

a 3% discount rate or $48 billion using a 7% discount rate3

. A large proportion of the 

monetized benefits results from avoiding premature death. The estimated benefits from 

avoided morbidity are approximately $510 million with a 3% discount rate and nearly 

$350 million with a 7% discount rate. Approximately 68% of the benefits are associated 

with reduced PM from NOx emissions, and the remaining 32% from direct PM 

emissions. 

Table 3: Undiscounted Unit Values for Health Effects 

(at various income levels in 2007 dollars) 1

Health Endpoint 2007 2010 2025 References 

Mortality

Premature death 

($ million) 

8.9 9.2 10 

U.S. EPA 

(1999, p. 70-72, 2000, 

2004, p. 9-121) 

Hospital Admissions 

Cardiovascular 

($ thousands) 36 37 54 CARB (2003), p. 63 

Respiratory 

($ thousands) 44 45 44 CARB (2003), p. 63 

Minor Illnesses 

Acute Bronchitis 452 455 471 U.S. EPA (2004), 9-158 

Lower Respiratory 

Symptoms 20 20 21 U.S. EPA (2004), 9-158 

Work loss day 191 201 260 2002 California wage data, U.S. Department of Labor 

Minor restricted 

activity day (MRAD) 64 64 67 U.S. EPA (2004), 9-159 

1

The value for premature death is adjusted for projected real income growth, net of 0.4 elasticity. Wagebased values (Work Loss Days) are adjusted for projected real income growth, as are WTP-derived 

values (Lower Respiratory Symptoms, Acute Bronchitis, and MRADs). Health endpoint values based on 

cost-of-illness (Cardiovascular and Respiratory Hospitalizations) are adjusted for the amount by which

projected CPI for Medical Care (hospitalization) exceeds all-item CPI. 

 

3

 CARB follows U.S. EPA practice in reporting results using both 3% and 7% discount rates. 
D-9 

E. Conclusion 

The health benefits of implementing the proposed regulation are substantial. Staff 

estimates that the cumulative emissions reductions over the lifetime of the rule can be 

associated with approximately 9,400 fewer premature deaths, 1,100 fewer hospital 

admissions due to respiratory causes, 1,200 fewer hospital admissions due to 

cardiovascular causes, 150,000 fewer cases of asthma-related and other lower 

respiratory symptoms, 12,000 fewer cases of acute bronchitis, 950,000 fewer work loss 

days, and 5,500,000 fewer minor restricted activity days. The uncertainty behind each 

estimated benefit ranges from about 15% to 75% for most endpoints. The estimated 

statewide benefits over 2010 to 2025 from these reductions in adverse health effects is 

$48 billion using a 7% discount rate or about $69 billion using a 3% discount rate. 

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