Engineering Sciences:
Environmental Impacts of Intercity Travel:
Amtrak, Commercial Airlines, and High-Speed Rail
FAN ZHONG ʼ06
Introduction
Both Europe and Japan boast extensive high-speed
rail systems for intercity transportation (Amtrak press
release 2002). The current international notion of “highspeed rail system” is one whose trains cruise at a velocity
above 125 mph. In France for instance, the Train Grande
Vitesse (TGV) runs at 185 mph (1).
In America, however, high-speed rail is much less
prevalent. A single corporation, Amtrak, holds a monopoly
over the national intercity passenger rail system. It sports
several “high-speed” routes, of which only one, the
Northeast Corridor (NEC), actually operates above 120
mph. The others need to be upgraded in order to support
such high speeds. However, financial complications
call into question the feasibility of upgrading and even
continued operation of these routes. Over the past several
decades, rail-travel has lost significant profitability and
popularity to America’s extensive Interstate Highway
system and numerous certified domestic commercial
(CDC) air carriers. Amtrak is now sustained by $1.23
Billion per year in federal subsidies (2).
These subsidies are sought by a number of public
interest groups in the United States which lobby fiercely
for government subsidization and expansion of the
American high-speed rail transportation – the Midwest
High Speed Rail Coalition (3), Friends of Amtrak (4)
and Save Amtrak (5) to name a few. Their activism is
based a two-pronged argument: 1. that rail travel is an
accessible form of transportation and an important
aspect of public infrastructure; 2. that Amtrak is
more environmentally sound than air-travel. The first
argument is a sociopolitical matter outside the scope
of natural sciences. The second argument is a matter of
science, but is so widely accepted that no systematic and
comprehensive proof of it has ever been compiled. It is
the objective of this paper is to evaluate this assertion
through scientific analysis. Proponents of Amtrak cite
the Congressional Research Service (CRS) Report for
Congress 96-22E statement: “Transportation by certified
air carriers on domestic routes consumes substantially
more Btu than Amtrak, and general aviation uses more
than three times as much energy as Amtrak,” as proof of
Amtrak as the “greener” mode of travel (6). The matter is
slightly more complicated that the CRS report presents
it to be. First, it is misleading to compare Amtrak with
general aviation. Amtrak is a mode of commercial public
transportation, whereas general aviation includes energy
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intensive special aircrafts such as helicopters, person jets,
and military aircrafts, which can hardly be considered
in the same category as public transportation. Only a
comparison between Amtrak and certified domestic
commercial (CDC) air carriers should be applied for
the purposes of this discussion. Moreover, an analysis
of environmental impact cannot be summed up simply
with fuel economy, one must also consider air pollution,
noise pollution, scope of impact, population exposed,
and the long- and short-term impacts on humans and
the landscape.
The air-travel industry consumes much more energy
than Amtrak, but also serves many more passengers over
longer distances. A long flight pollutes only slightly more
than a flight half its length. Trains can cover the same
mileage with completely different impact rates depending
on how often they stop. Passengers may be inclined to
make short trips via rail and long one via air. To simplify
this highly complex problem, for the quantitative analysis,
this paper shall evaluate pollution as the average impact
rate per passenger-mile (p-m).
Fuel Economy
In terms of the percentage of total energy
consumption within the transportation sector, air
travel consumes over four times as much energy as
does Amtrak (Inventory Table 1). However, because the
two modes of transportation do not service the same
number of passengers, nor cover the same mileage, that
ratio does not mean much by itself. Conventionally, the
comparative energy efficiency of transportation modes
is rated by “fuel economy.” In the case of commercial
transportation, fuel economy can be best assessed as the
average amount of fuel it takes for one passenger to travel
one mile. According to the 2002 National Transportation
Statistics, the energy consumption per passenger-mile for
Amtrak is 2,000 BTU per p-m (British Thermal Units
per passenger-mile), less than half that of commercial
airlines, a whooping 4,049 BTU per p-m (Inventory
Table 1). This does not necessarily
mean that trains pollute
less. Conventional Amtrak
trains burn diesel fuel
(whereas most European
and Japanese trains
are electric), and
trainset 213 (power car 28026)
airplanes burn jet fuel. Duplex
at Gare de Lyon in Paris, 15 June 1997.
anfred
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DARTMOUTH UNDERGRADUATE JOURNAL OF SCIENCE
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Acela Express train 2175
drifting through a curve
south of Back Bay, Boston,
on 03 May 2001.
Air Pollution
Any discussion of pollution should involve scope.
Where is the pollution emitted, and what is its area of
impact? It seems natural to assume that since most of air
travel is done far above ground, the bulk of its pollution
occurs very high in the atmosphere, and has little impact
on human health and ground level ecological systems.
However, planes consume fuel when their engines are
producing some level of thrust. Only take-off occurs at
full-thrust; landing and taxing in and out occurs at 1/6
thrust; cruising in the air requires negligible thrust, and
very little energy (8). Hence the bulk of a plane’s fuel
consumption occurs near or at ground-level, as does
most of its air pollution.
Air Pollutants: Health and Ecological
Impacts:
The US Environmental Protection Agency evaluates
transportation air pollution in terms of the following
five major pollutants: carbon monoxide, nitrogen oxides,
sulfur dioxide, hydrocarbons (specifically volatile organic
compounds), and particle matter (carbon, soot, fly ash,
etc.). Let us examine the ecological and public health
impacts of each of these pollutants. In the air-travel
industry, air pollution is concentrated in the atmosphere
at ground level or not far above it, in a small radius
around airports. The air pollution by Amtrak is spread
out throughout the areas near its stations and along its
tracks.
Carbon Monoxide
Carbon monoxide is produced as a byproduct of
incomplete combustion in the presence of insufficient
oxygen. It is toxic to all warm-blooded animals. Inhalation
of CO causes destruction to the central nervous system.
Exposure is categorized into acute and chronic forms.
Studies show a 25%-40% death-rate among people who fall
SPRING 2004
by Clem Tillier, accessed via http://www.trainweb.org/tgvpages/images/acela/
Due to the fractional distillation method of petroleum
production, the environmental impacts of producing
diesel fuel and producing jet fuel are roughly comparable.
However, air pollution caused by the combustion of
diesel is drastically more severe than that of jet-fuel (7).
victim to acute CO poisoning, and 15-40% of those who
survive suffer immediate or delayed neuropsychological
deficit. In the case of public transportation, we are
primarily concerned with exposure to low levels of CO
near airports and train stations. For passengers, exposure
to CO may cause slight headache, nausea, weakness, and/
or dizziness. Chronic CO poisoning is an occupational
hazard for airline and Amtrak employees and an
environmental hazard for residents of neighborhoods
near airports, train stations and railways. This type of CO
poisoning is not fully documented because it has similar
symptoms as, and is therefore often misdiagnosed as
chronic fatigue syndrome, a viral or bacterial pulmonary
or gastrointestinal infection, a “run-down” condition,
and immune deficiency (9).
Nitrogen Oxides, Sulfur Oxides, and Hydrocarbons
The various nitrogen oxides are categorized together
as NOx compounds. NOx react with water to form nitric
acid, which falls out in rain. Sulfur oxides, too, react with
water and oxygen to form acid rain. Although the bulk of
sulfur and nitrogen oxide emissions come from electric
utility plants and automobiles, air and rail transportation
do contribute, too, to acid-rain production. Acid-rain
damages vegetation and corrodes paint over time. It strips
the soil of nutrients and minerals as it percolates down
into the ground, gradually limiting plant growth and the
soil’s ability to buffer vegetation from toxic substances
(10). Furthermore, acid lakes cannot sustain healthy
aquatic ecosystems.
The combination of NOx and hydrocarbons in
sunlight produces photochemical smog, which includes
ozone. Ozone is not only toxic to humans but also
contributes to global climate change. Ground-level
ozone causes health problems such as difficult breathing,
lung damage, and reduced cardiovascular functioning.
Atmospheric ozone is a greenhouse gas. The formation
of ozone from NOx and HC emission exacerbates global
warming (11).
Hydrocarbons are emitted by evaporation of fuels
before combustion – such as around refueling locations,
also as part of the exhaust from incomplete fuel
combustion. HCs are themselves toxic, causing cancer
and other health problems (12).
Particulate Matter
Commonly known as soot or fly ash, particulate matter
is the leftover carbon and impurities from the combustion
of fossil fuels. Particulate matter comes in different sizes.
Both the larger “respirable PM” and the smaller “fine PM”
cause risk of respiratory disease, lung damage, cancer, and
premature death in humans. They reduce visibility, which
leads to annoyances such as blurred scenic views and safety
hazards such as reduced airport safety (13).
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Diesel Trains
Conventional Amtrak Trains vs. Commercial Airlines
As stated earlier, air travel requires over twice as
much fuel per passenger-mile as rail travel. Though fuel
consumption usually correlates to air pollution, one must
by careful in drawing conclusions about air-pollution
from that alone. A crucial point to take into account in
calculating pollution emissions is fuel type. Commercial
passenger planes consume jet fuel, a highly refined and
clean-burning gasoline. Conventional Amtrak intercity
trains burn diesel, a much cruder fuel notorious for
its high impurity. The latest available estimates of fuel
intensity; emissions rates of diesel and jet fuels; annual
energy consumption, revenue passenger-miles, and
available seat-miles of Amtrak and Certified Domestic
Commercial (CDC) airlines can be found in the 2002
National Transportation Statistics Report (14), accessible
via the US Bureau of Transportation Statistics (US
BTS). This data is used to compute the average grams of
pollutants per passenger-mile (g/p-m) output for both
conventional Amtrak trains and CDC airplanes in Results
Table 2 and Figure 1.
At Full Capacity: Conventional Amtrak Trains vs.
Commercial Airlines
Supporters of Amtrak like to point out Amtrak’s low
rider-ship as a source of energy inefficiency, and increased
pollution rates. Indeed, annual national transportation
statistics show that planes operate on average at 54.76%
of full capacity, while Amtrak achieves only 35.9%. (see
Results Tables 3 and 4). The hypothetical emission
rates for Amtrak and CDC Airlines at full capacity can
be calculated with the methods in Calculations 1 and 2,
replacing their total annual passenger-miles with total
annual seat-miles.
Results Table 5 and Figure 2 show that contrary to
what people may believe, even if both Amtrak and CDC
Airlines were operating at full capacity, Amtrak’s air
pollution rates would at best be comparable to that of
domestic commercial airlines.
Results Table 5: At Full Capacity: Conventional Amtrak vs. CDC
Airlines
Electric Trains:
Amtrak has a 30% lower CO production level than
CDC airlines, but it produces at a 21% higher HC level
and PM, SO2 and NOx levels many times higher than
that of airplanes. The negative impacts of particulate
matter, cancer-causing hydrocarbons and toxic ozone,
climate-disrupting atmospheric ozone, and ecologicallydisruptive acid rain far exceed the advantages of a lower
CO emission rate. Conventional Amtrak trains pollute
just as much if not more than airplanes.
Acela Express vs. Commercial Airlines
The poster-child of the emerging US high-speed rail
system is the Northeast Corridor Acela Express (Photo
Set 1). Acela trains are manufactured by the Canadian
company Bombardier, and modeled after the French TGV
(Photo Set 2). The trains run on electricity, and of course,
generate no or negligible air pollution en-route. But they
are indirectly responsible for air-pollution generated
at stationary power plants that supply the necessary
electricity. Large-scale production is known to maximize
efficiency, and stationary power plants are better able
to effectively control pollution than mobile sources.
Figure 1: Conventional Amtrak vs. CDC Airlines x-axis (pollutant) yaxis (g/p-m)
Figure 2: At Full Capacity: Conventional Amtrak vs. CDC Airlines xaxis (pollutant) y-axis (g/p-m)
Results Table 2: Conventional Amtrak vs. CDC Airlines
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DARTMOUTH UNDERGRADUATE JOURNAL OF SCIENCE
Logically, electrically-run high-speed trains should have
lower overall air-pollution output than airplanes.
Indeed, the TGV is a very clean mode of transportation
in France, where over half of the electricity is generated by
air-pollution-free nuclear power plants (which no doubt
produce its own type of pollution – nuclear waste). In the
US, however, the bulk of our total domestic electricity
(70.8%) is produced from the combustion of coal, gas,
and oil. Only 19.8% is from nuclear fusion, and 7.2%
from hydro-power (Inventory Table 9).
According to Amtrak’s official statistics, the Acela has
a fuel efficiency of 1200 BTU per passenger-mile (15). To
translate that into grams of air-pollutants per passengermile, we must look at the air-pollution rates of power
plants (See Inventory Table 10).
The average modern power plant uses fuel with 2%
sulfur content and 10% ash content. Uncontrolled, this
could lead to dangerous levels of SO2 and PM emissions.
Indeed, the cities and towns near coal-burning power
plants were smothered with foul smog and soot not long
ago in the US, and are still so inflicted in developing
countries. Currently, the US Clean Air Act emission
standards limit sulfur and particle matter emissions from
electricity production to 260g of SO2 and 13g of PM per
million kJ of energy input. With the help of sophisticated
scrubbers and bag-houses, power-plants have reduced
their pollution output by over 85% for SO2 and 99% for
PM (16).
Inventory Table 12 shows the thermal conversion
factors for different types of coal, oil, and gas. For the sake
of simplicity, let us approximate the energy to mass ratio
of coal to be 30 MJ/kg, oil to be 40 MJ/kg, and gas to be 40
MJ/kg. While the latest power plant models have achieved
40% energy efficiency, the rule of thumb for operating
power plants in the US is that their production output is
1/3 of their production input (16). Also, there is a roughly
5% energy loss in conveying electricity from the power
plants to the electric tracks.
To derive the average pollutant emission per
passenger-mile traveled on the Acela, assuming all the
trains are powered by electricity from US coal-, oil- or
gas-burning power plants1, we must take into account
the pollutant content to fuel-mass ratio and thermal
Figure 3: Acela vs. CDC Airlines x-axis (pollutant) y-axis (g/p-m)
SPRING 2004
Results Table 8: Acela vs. CDC Airlines
conversion factors for fuels, the efficiency of power
production and transfer, and the energy intensity of the
Acela to calculate pollution rate by fuel type (Calculation
5), and take the weighted average of these pollutant
rates according to the US electricity production mode
breakdown in Inventory Table 9.
Results Table 8 and Figure 3 show that even if
Acela trains ran purely on electricity produced by the
not-so-clean coal, oil, and gas burning plants, they
would still generate far less HC, CO, NOx, and PM per
passenger-mile than airplanes. The high SO2 emission
from electricity production is worth noting. However,
the clean-air benefits of electric trains far outweigh the
adverse effects of this extra SO2 output.
Finally, a crucial advantage that electric Acelas have
over airplanes and conventional Amtrak trains is that all
types of air pollution it causes is “elsewhere pollution.”
There is a choice of pollution location. Unlike airports
and conventional rail tracks, power plants can be located
in areas where their emissions may have smaller impacts
on the regional human population and the environment.
Noise Pollution:
Conventional Amtrak Trains
People who live near airports often complain about
the noise. They are right to complain. Residential areas
near airports often suffer lowered property values due
to noise pollution. Strictly in terms of loudness, 55 to 60
dBA is the “acceptable” noise level for residential areas.
The human threshold for pain is 125 dBA, but exposure
to noise levels below that threshold can be hazardous
as well. According to the Organization for Economic
Cooperation and Development, exposure to noise
higher than 75 dBA causes potential health effects such
as changes in motor coordination (17). Airplane takeoffs and landings generate noise levels far above 75dBA.
One assumption made by the supporters of Amtrak is
that increased train-travel would decrease air-traffic
and thereby alleviate airport noise pollution, which this
report has disproved.
To put dBA numbers into perspective, the following
are examples of everyday noise levels: urban daytime
– 80 dBA; diesel truck at 150ft – 90 dBA; inside of a New
York City subway train – 100 dBA; and quiet suburban
nighttime – 40 dBA (18).
The noise level for planes ranges from 90 to 104
dBA on take off and 83 to 95 dBA on landing. From the
perspective of a resident near an airport, the average noise
15
Inventory Table 13: Transportation Noise Levels (Golden, 1979) The
above table is EPA data of noise levels generated by conventional
diesel trains and different sized commercial airplanes.
average 82 mph from Washington D.C to New York and
55 mph from New York to Boston (19).
In order for the US to adopt a high-speed system,
a brand-new, relatively straight and level high-graded
rail system must be constructed. This would take up
large swathe of land that extends in a straight line from
one major city to the next. Deep trenches must be cut
through this land must to lay level enough tracks. The
landscape and ecological disruption involved in such a
construction project are considerable.
Conclusion
Photo by Yann Nottara ([email protected])
Contrary to popular belief, conventional Amtrak
level generated by planes lies in the 90-95 dBA range. On
trains
are not at all more environmentally friendly than
the other hand, a passing train generates noise level of
commercial
airplanes for intercity travel. High-speed
100 dBA, and the loudness of its whistle approaches the
human threshold for pain. Surprisingly, trains are louder electric Acelas are cleaner than airplanes in terms of fuel
than planes. In addition, the noise planes generate affects economy, air pollution and noise pollution. However,
in order for the US to adopt a highhumans only during take off and landing.
speed system, a separate high-graded
During most of their flight, planes are
rail system must be constructed. The
high above ground and out of our hearing
financial/social costs and land disruption
range. On the other hand trains generate
of taking on such a project far outweigh
all of their noise at ground level, creating
the benefits of having a high-speed rail
more overall noise impact.
system.
The impact of rail travel is spread
Proponents of high-speed rail
out across the countryside so that the
in America point to the European and
average individual community suffers
through the loud chuck-chuck and the The Scharfenberg coupler on a TGV Japanese systems as examples. Yes, highhigh-pitched choo-choo only two or three Duplex power car. This automatic speed intercity rail works in Europe
is used when two trainsets and in Japan. It works for four reasons.
times a day. Airplane noise pollution, coupler
are hooked together to make a higher
however, is concentrated around airports, capacity train (in this case, up to 1090 One, trains are heavily subsidized in
which generate noise almost incessantly. seats). The horizontal gray door above Europe and Japan as a part of their
the mating plate protects the electrical
Psychologically, people are more inclined and pneumatic connections. The public infrastructure. Two, gasoline
to notice concentrated nuisances at “thumb” protruding forward serves is heavily taxed in Europe. The cheap
properly align the couplers as America gasoline and well-developed
specific locations than a nuisance that to
they approach each other. It actually
spreads out its impact. Also, the visual of sticks out of the nose fairing and is Interstate Highway system makes travel
by automobile the significantly more
planes hovering overhead heightens our sometimes taken for a Pitot tube!
attractive here than in Europe. Three,
awareness of its noise levels. People are
Europe
relies
more
heavily on nuclear power for electricity
likely to perceive the high-pitched noise of takeoffs and
landings as noxious and the rumble of passing trains as production than the US. Nuclear power makes up for 80%
of the French power production, as opposed to 20% in
nostalgic and even soothing.
the US. In terms of air pollution, electricity from nuclear
fission is significantly cleaner than that from coal and oil
High-Speed Amtrak System
Five major rail corridors: the Pacific Northwest, combustion (the main source of US power-production).
the Chicago Hub, the Gulf Coast, the Southeast, the Thus European electric trains also cause significantly less
Northeast and Empire have been designated as high- air pollution than American electric trains. Four, Europe
speed corridors. High-speed trains operate or will operate is miniature in comparison to the United States. One can
on them, but not at very high speeds. 97% percent of the ride the Chunnel from Paris to London in 2:30 hours,
tracks on which Amtrak operates are owned by freight the Eurostar from Amsterdam to Frankfort in 5:19 hours
companies. Amtrak’s Acelas not only have to run on low- (20). It takes 18:30 hours to get from New York City to
grade, ill-maintained tracks, but have to share tracks with Chicago and 41:00 hours from Chicago to LA via Amtrak
slow freight trains. They can only operate at top speeds (21). Granted the Eurostar is high speed and Amtrak is
of 79 mph or less on most of the existing system. In the not, it is undoubtedly time-consuming to travel on land
best case of the Northeast Corridor, brand-new Acelas in the US, making air travel the more attractive option in
that have top speeds of 150 mph or more are only able to the US.
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DARTMOUTH UNDERGRADUATE JOURNAL OF SCIENCE
High-speed rail may be an attractive form of public
transportation for Europe and Japan, but due to the
fundamental differences between the US and the Old
World in terms of energy policy, power production,
culture and sheer size, the most economically and
environmentally viable transportation option for them
may not be so for us.
Footnotes
1
The two other major domestic power production
modes are nuclear and hydro, which only account for
about 1/5 of US electricity production. In a study of
ecological impacts in the US, it is not a stretch to use the
fuel-combustion impact to estimate the impact of powerproduction. This would not be the case in other countries
such as France, where nuclear and hydro power account
for nearly 80% of its national electricity production (22).
Note: due to space constraints, appendices were
not included in the print edition of this article.
For data in excluded appendices, please visit
www.dartmouth.edu/~dujs
REFERENCES
1. “Amtrak unveils new high-speed service for Northeast,” CNN
Travel Guide News, 9 March 1999, http://www.cnn.com/TRAVEL/
NEWS/9903/09/bullet.train/.
2. “Forecasts say refund checks to increase,” The Seattle Times,
14 November 2003, http://seattletimes.nwsource.com/cgi-bin/
PrintStory.pl?document_id=2001791061&zsection_id=268448413&sl
ug=watch14&date=20031114.
3. http://www.midwesthsr.com.
4. http://www.trainweb.org/cocon/amtrak.html.
5. http://www.saveamtrak.org.
6. S. J. Thompson, “Amtrak and Energy Conservation in Intercity
Passenger Transportation” (Congressional Research Service Report.
96-22 E. 1996; http://www.ncseonline.org/NLE/CRSreports/energy).
7. US Environmental Protection Agency, National Air Quality and
Emissions Trends Report, Appendix A (1999; http://www.epa.gov/
oar/aqtrnd98).
8. P. Collopy, personal communication.
9. D. G. Penney, Carbon Monoxide, CRC Press (1996).
10. “Acid Rain Threatens Future Productivity of Forests,” Science
Daily, 15 March 1999.
11. US Environmental Protection Agency, Mobile Source Emissions
– Past, Present, and Future (1999; http://www.epa.gov/otaq/invntory/
overview/pollutants/hydrocarbons.htm).
12. “Chemists Identify Missing Nitrogen Oxide Pollutant
in Atmosphere,” Science Daily, 26 March 2002 (http://
www.sciencedaily.com/releases/2002/03/020326073218.htm).
13. Rail Power Technologies Corps, Air Pollution Sources, Health
Effects, and Controls (http://www.railpower.com/particlematter.php).
14. Bureau of Transportation Statistics, National Transportation
Statistics (BTS02-08 2002; http://www.bts.gov/publications/nts/2002/
index.html).
15. Acela Express Brochure (2002; http://Amtrak.com).
16. G. M. Masters, Introduction to Environmental Engineering and
Science (Prentice Hall, New Jersey, ed. 2, 1998), p. 25.
17. Organization for Economic Cooperation and Development,
Impact of Heavy Freight Vehicles, Paris (OECD Report RR/API/82-3
1982).
18. Landrum, Brown, “Common Noise Sources” (2001; P:\pvd00\gis\
arcview\images\common_noise_sources.cdr).
19. D. R. Peterman, Amtrak: Overview and Options (CRS Report for
Congress RL30659 January 2001; http://www.ncseonline.org/NLE/
CRSreports/Transportation/trans-36.cfm?&CFID=8128636&CFTOK
EN=20370242).
20. Mele’s Travel Europe Resource Center, Point to Point Rail Prices
and Travel Time Estimates (2003; http://meleterc.com/Page6railpttopt
.html#Amsterdam).
22. “France’s Nuclear Option,” BBC News Online, 9 October 2003.
Interested in science-writing or research? Being on staff is a great
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SPRING 2004
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