Fuel efficiency in transportation
This page describes
fuel efficiencyin means of transportation. For the environmental impact assessmentof a given productor service throughout its lifespan, see life cycle assessment.
Comparing Fuel efficiency in transportation is a bit like comparing apples and oranges in some ways. Here are a few things to consider. Traction energy Metrics produced by the UK Rail and Safety Standards Board is also a useful review of the problem of comparison http://www.rssb.co.uk/pdf/reports/research/T618_traction-energy-metrics_final.pdf
* There is a distinction between vehicle MPGe and passenger MPGe. Most of these entries cite passenger MPGe even if not explicitly stated. It is important not to compare energy figures that relate to unsimilar journeys. An airline jet cannot be used for an urban commute so when comparing aircraft with cars the car figures must take this into account.
* There is currently no agreed upon method of comparing
electric vehicleefficiency to heat engine( fossil fuel) vehicle efficiency. However, current typical emissions and thermal energy consumption can be compared. Vehicle speed is also an important parameter, and a peer-reviewed evaluation which convolves these criteria may be found at http://www.bentham-open.org/pages/content.php?TOEFJ/2008/00000001/00000001/11TOEFJ.PDF
* If the issue is rapid investment in new electric mass transit it is important to use emissions associated with the most polluting fuel because increased demand for electricity increases the use of the most polluting fuel used in generation for the immediate future.
* Systems that re-use vehicles like trains and buses can't be directly compared to vehicles that get parked at their destination. They use energy to return (less full) for more passengers and must sometimes run on schedules and routes with little patronage. These factors greatly affect overall system efficiencies. The energy costs of accumulating load need to be included. In the case of most mass transit distributing and accumulating load over many stops means that passenger kilometres are inherently a small proportion of vehicle kilometres see Transport Energy Metrics, Lessons from the west Coast Main line Modernisation and figures for London Underground in transport statistics for Great Britain 2003. Lessons from the west coast mainline modernisation suggest that long passenger rail should operate at less than 40% capacity utilisation and for London underground the figure is probably less than 15%.
* Most cars run at less than full capacity, with the usual average load being between 1 and 2. Cars are also subject to inefficiencies because of congestion and the need to negotiate road junctions. The impact of transport road building to reduce congestion should always be considered as should the improving efficiency of cars see http://www.hm-treasury.gov.uk/media/9/5/pbr_csr07_king840.pdf,
* Vehicles are not isolated systems. They usually form a part of larger systems whos design inherently determines energy consumption. Judging the value of transport systems by comparing the performance of their vehicles alone can be misleading. For instance, metro systems may have a poor energy efficiency per "passenger kilometer", but their high throughput and low physical footprint makes the existence of high urban population densities viable. Total
energy consumptionper capita declines sharply as population density increases, since journeys become shorter. [cite book
coauthors= Jeffrey R. Kenworthy
title= Sustainability and Cities: Overcoming Automobile Dependence
publisher= Island Press
* See also Logistics and Transport Focus (the Journal of the Charter Institute of Transport)vol 9 number10 through volume 10 number 6 for a series of articles debating the general issues of fuel efficiency in transportation in the context of impact on climate change
Hybrid electric vehicles are the best bet to get the most out of each tank of fuel during city driving [ [http://editorial.autos.msn.com/article.aspx?cp-documentid=434544 Top 10 Fuel Misers - MSN Autos ] ] [ [http://www.fueleconomy.gov Fuel Economy ] ] .
freighttransport, rail and ship transportare generally much more efficient than trucking, and air freightis much less efficient. (See [http://technology.newscientist.com/data/images/archive/2669/26691701.jpggraph] [David Strahan, [http://technology.newscientist.com/channel/tech/mg19926691.700-green-fuel-for-the-airline-industry.html "Green fuel for the airline industry"] , New Scientist, 13 Aug. 2008, pp. 34-7.] )
* Walking or running one kilometre requires approximately 70 kcal or 330 kJ of
food energy[http://www.brianmac.demon.co.uk/energyexp.htm Energy expenditure for walking and running ] ] . This equates to about MPGe|235 in terms of gasolineenergy.
* Cycling requires about 120 kJ per km which equates to approximately MPGe|653.
* Data from the Metropolitan Transport Commission for the nine-county San Francisco Bay Area, states an automobile occupancy rate of about 1.3 passengers per car. [ [http://www.mtc.ca.gov/maps_and_data/datamart/forecast/ass98_tab8.htm MTC - Maps and Data ] ]
* In 2006, the average occupancy for cars in the UK was 1.58.cite web |title=Transport trends: current edition |date=
2008-01-08|publisher=UK Department for Transport|url=http://www.dft.gov.uk/pgr/statistics/datatablespublications/trends/current/ |accessdate=2008-03-23]
* The Oak Ridge National Laboratory (ORNL) state that the energy content of 1 U.S gallon of unleaded gasoline is 115,000 BTU or 32 MJ/L and that of 1 U.S. gallon of diesel is 130,500 BTU or 36.4 MJ/L. [ [http://bioenergy.ornl.gov/papers/misc/energy_conv.html Oak Ridge National Laboratory (ORNL)] ]
* The Volkswagen Polo 1.4 TDI Bluemotion and the Seat Ibiza 1.4 TDI Ecomotion, both rated at L/100km|3.8 (combined) are the most fuel efficient cars on sale in the UK as of
2008-03-22. [cite web |title=Best on CO2 rankings |url=http://www.dft.gov.uk/ActOnCO2/index.php?q=best_on_co2_rankings |publisher=UK Department for Transport|accessdate=2008-03-22] [cite web |title=Vehicle details for Polo 3 / 5 Door (from NOV 06 Wk 45>) 1.4 TDI (80PS) (without A/C) with DPF BLUEMOTION M5 |publisher=UK Vehicle Certification Agency |url=http://www.vcacarfueldata.org.uk/search/vehicleDetails.asp?id=20690 |accessdate=2008-03-22] [cite web |title=Vehicle details for Ibiza ( from NOV 06 Wk 45 > ) 1.4 TDI 80PS Ecomotion M5 |publisher=UK Vehicle Certification Agency |url=http://www.vcacarfueldata.org.uk/search/vehicleDetails.asp?id=20471 |accessdate=2008-03-22] Accounting for Diesel fuel gives us MPGe Diesel|MPGe mpgimp|74.3.
Honda Insightwas rated mpg|70 highway.Fact|date=March 2008
Honda Civic Hybrid- The second most energy efficient automobile in the U.S., it regularly averages around 45 miles per gallon.
Toyota Prius- According to the U.S. EPA's revised estimates, the combined fuel consumption for the 2008 Prius is mpg|46, [cite web|url=http://www.fueleconomy.gov/feg/noframes/24882.shtml|title=2008 Toyota Prius|publisher=EPA|accessdate=2007-12-25] making it the most fuel efficient U.S. car of 2008.cite web
title=2008 Most and Least Fuel Efficient Vehicles (ranked by city mpg)
publisher=United States Environmental Protection Agency and United States Department of Energy
accessdate=2007-12-25] In the UK, the official fuel consumption figure (combined) for the Prius is L/100km|4.3.cite web |title=Vehicle details for Prius 1.5 VVT-i Hybrid E-CVT |publisher=UK Vehicle Certification Agency |url=http://www.vcacarfueldata.org.uk/search/vehicleDetails.asp?id=10982 |accessdate=2008-03-22]
General Motors EV1was rated in a test with a charging efficiency of 373 Wh-AC/mile or MPGe kWh|1/.373 . [http://www1.eere.energy.gov/vehiclesandfuels/avta/pdfs/fsev/eva_results/ev1_eva.pdf]
*The four passenger GEM NER also uses 169 Wh/mile or MPGe kWh|1/.169, [ [http://www1.eere.energy.gov/vehiclesandfuels/avta/pdfs/nev/gem2005e4.pdf NEV America U.S. Dept. of Energy Field Operations Program - 2005 Global Electronic Motorcars e4 4-Passenger ] ] which equates to MPGe kWh|4/.169 for four passengers , albeit at only convert|24|mph|km/h|abbr=on.
hydrogenis no more a source of energy than electricity is, the 50-70% efficiency of producing hydrogen has to be combined with the vehicle efficiency, so for example a hydrogen vehiclewhich gets MPGe|27 is actually getting only about MPGe|16. [ [http://www1.eere.energy.gov/vehiclesandfuels/avta/pdfs/hicev/sae_hydrogen_presentation_2006.pdf Hydrogen Internal Combustion Engine (ICE) Vehicle Testing Activities ] ]
* Airbus state that their
A380consumes fuel at the rate of less than 3 L/100 km per passenger. [cite web |title=The A380: The future of flying |publisher=Airbus |url=http://www.airbus.com/en/myairbus/airbusview/the_a380_the_future_of_flying.html |accessdate=2008-03-22] CNN reports that the fuel consumption figures provided by Airbus for the A380, given as 2.9 L/100 km per passenger, are "slightly misleading", because they assume a passenger count of 555, but do not allow for any luggage or cargo. [cite news |title=Green light for the new A380 |author=Matthew Knight |date= 2007-10-26|publisher=Cable News Network |work=CNN.com |url=http://www.cnn.com/2007/TECH/10/25/fsummit.climate.A380/index.html |accessdate=2008-03-23] Typical occupancy figures are unknown at this time.
* Passenger airplanes averaged 4.8 L/100 km per passenger (1.4 MJ/passenger-km) (49 passenger-miles per gallon) in 1998.Fact|date=March 2008 Note that on average 20% of seats are left unoccupied. Aircraft efficiencies are improving: Between 1960 and 2000 there has been a 70% overall fuel efficiency gain. [ [http://www.transportenvironment.org/docs/Publications/2005pubs/2005-12_nlr_aviation_fuel_efficiency.pdf National Aerospace Laboratory] ]
* NASA and Boeing are conducting tests on a 500 lb. "blended wing" aircraft. This design allows for greater fuel efficiency since the whole craft produces lift, not just the wings. [ [http://www.ecogeek.org/content/view/871/ Ecogeek Article] ]
* The Sikorsky S-76C++ twin turbine helicopter gets about 1.65 mpg at 140 kn and carries 12 for about 19.8 passenger-miles/gal.Fact|date=March 2008
* Cunard state that their liner, the
RMS Queen Elizabeth 2, travels convert|49.5|ft|m|abbr=on per convert|1|impgal|l|3 of diesel oil, and that it has a passenger capacity of 1777. [cite web |title=Queen Elizabeth 2: Technical Information |publisher=Cunard Line |url=http://www.cunard.com/uploads/QE2_Tech.pdf |accessdate=2008-03-31] From those figures, fuel consumption can be calculated as convert|0.009375|mpgimp|L/100 km. Carrying 1777 passengers, that equates to convert|16.7|mpgimp|L/100 km per passenger.
* Freight: the AAR claims an energy efficiency of over 400 short ton-miles per gallon of diesel fuel in 2004 [ [http://www.aar.org/getFile.asp?File_id=364 Railroads: Building a Cleaner Environment] ,
Association of American Railroads] (0.588 L/100 km per tonne or 235 J/(km·kg))
East Japan Railway Companyclaims for 2004 an energy intensity of 20.6 MJ/car-km, or about 0.35 MJ/passenger-km [ [http://www.jreast.co.jp/e/environment/pdf_2005/report2005e_22_23.pdf Environmental Goals and Results] , JR-East Sustainability Report 2005]
* a 1997 EC study [ [http://www.inrets.fr/infos/cost319/MEETDeliverable17.PDF Estimating Emissions from Railway Traffic] ] on page 74 claims 18.00 kWh/train-km for the
TGV Duplexassuming 3 intermediate stops between Parisand Lyon. This equates to 64.80 MJ/train-km. With 80% of the 545 seats filled on average [ [http://themes.eea.europa.eu/Sectors_and_activities/transport/indicators/technology/TERM29,2001/Occupancy_rates_TERM_2001.pdf European Environment Agency Occupancy Rates, page 3] ] this is 0.15 MJ/passenger-km.
* Actual train consumption depends on gradients, maximum speeds and stopping patterns. Data was produced for the European MEET project (Methodologies for Estimating Air Pollutant Emissions) and illustrates the different consumption patterns over several track sections. The results show the consumption for a German ICE High speed train varied between around 19 kWh/km to 33 kWh/km. The data also reflects the weight of the train per passenger. For example, the
TGVdouble-deck ‘Duplex’ trains use lightweight materials in order to keep axle loads down and reduce damage to track, this saves considerable energy. [ [http://www.cfit.gov.uk/docs/2001/racomp/racomp/a1.htm Commission for integrated transport, Short haul air v High speed rail] ]
* A Siemens study of
Combinolight rail vehicles in service in Basel, Switzerlandover 56 days showed net consumption of 1.53 kWh/vehicle-km, or 5.51 MJ/vehicle-km. Average passenger load was estimated to be 65 people, resulting in average energy efficiency of 0.085 MJ/passenger-km. The Combino in this configuration can carry as many as 180 with standees. 41.6% of the total energy consumed was recovered through regenerative braking. [ [http://www.siemens.com/Daten/siecom/HQ/TS/Internet/Transportation_Systems/WORKAREA/reinhold/templatedata/English/file/binary/20661combino_tests_20661.pdf Combino - Low Floor Light Rail Vehicles Tests, Trials and Tangible Results] ]
* A trial of a
Colorado Railcardouble-deck DMU hauling two "Bombardier Bi-level coaches" found fuel consumption to be 128 US gallons for 144 miles, or 1.125 mpg. The DMU has 92 seats, the coaches typically have 162 seats, for a total of 416 seats. With all seats filled the efficiency would be 468 passenger-mpg, with 70%Fact|date=March 2008 filled the efficiency would be 328 passenger-mpg. [ [http://www.coloradorailcar.com/trirailtest.htm Colorado Railcar: "DMU Performs Flawlessly on Tri-Rail Service Test"] ]
* Note that intercity rail in the U.S. reports 3.17 MJ/passenger-km which is several times higher than reported from Japan. Independent transportation researcher David Lawyer attributes this difference to the fact that the losses in electricity generation may not have been taken into account for Japan [ [http://www.lafn.org/~dave/trans/energy/fuel-eff-20th-3.html#japan_ Fuel Efficiency of Travel in the 20th Century, Appendix] ] and that Japanese trains have a larger number of passengers per car. [ [http://www.lafn.org/~dave/trans/energy/fuel-eff-20th-2.html#_japan Fuel Efficiency of Travel in the 20th Century] ]
* Modern electric trains like the
shinkansenuse regenerative brakingto return current into the catenary while they brake. This method results in significant energy savings, where-as diesel locomotives (in use on unelectrified railway networks) typically dispose of the energy generated by dynamic braking as heat into the ambient air.Fact|date=February 2007
* This Swiss Railroad company
SBB-CFF-FFScites 0.082 kWh per passenger-km for traction. [http://mct.sbb.ch/mct/en/umweltbericht_02-03.pdf SBB Environmental Report 2002/2003] ]
* AEA carried out a detailed study of road and rail for the United Kingdom Department for Transport. [http://www.dft.gov.uk/stellent/groups/dft_railways/documents/page/dft_railways_611287.pdf Final report]
* Amtrak reports 2005 energy use of 2,935 BTU per passenger-mile [ [http://www.amtrak.com/servlet/ContentServer?pagename=Amtrak/am2Copy/Title_Image_Copy_Page&cid=1093554056875&c=am2Copy&ssid=565 Amtrak - Inside Amtrak - News & Media - Energy Efficient Travel ] ] , or 39 passenger-miles per gallon
* The Passenger Rail (Urban and Intercity) and Scheduled Intercity and All Charter Bus Industries Technological and Operational Improvements - FINAL REPORT states that "Commuter operations can dissipate more than half of their total traction energy in braking for stops." and that "We estimate hotel power to be 35 percent (but it could possibly be as high as 45 percent) of total energy consumed by commuter railways." [ [http://www.tc.gc.ca/programs/environment/climatechange/subgroups1/Main_Table/study1/Final_Report/Final_Report.htm#_Toc474834390 Bus and Rail Final Report ] ] Having to accelerate and decelerate a heavy train load of people at every stop is inefficient despite
regenerative brakingwhich can recover typically around 20% of the energy wasted in braking.
*In July 2005, the average occupancy for buses in the UK was stated to be 9. [cite web |title=Passenger Transport (Fuel Consumption) |date=
2005-07-20|publisher=UK House of Commons |work=Hansard |url=http://www.publications.parliament.uk/pa/cm200506/cmhansrd/vo050720/text/50720w26.htm#50720w26.html_sbhd1 |accessdate=2008-03-25]
*The fleet of 244 1982
New Flyer40 foot trolley buses in local service with BC Transitin Vancouver, BC, Canada in 1994/95 consumed 35454170 kWh for 12966285 vehicle-km, or 9.84 MJ/vehicle-km. Exact ridership on trolleybuses is not known, but with all 34 seats filled this would equate to 0.32 MJ/passenger-km. It is quite common to see standees on Vancouver trolleybuses. Note that this is a local transit service with many stops per km; part of the reason for the efficiency is the use of regenerative braking.
*A diesel bus commuter service in Santa Barbara, CA, USA found average diesel bus efficiency of 6.0 mpg (using MCI 102DL3 buses). With all 55 seats filled this equates to 330 passenger-mpg, with 70% filled the efficiency would be 231 passenger-mpg. [ [http://www.nrel.gov/docs/fy00osti/26758.pdf Demonstration of Caterpillar C-10 Duel-Fuel Engines in MCI 102DL3 Commuter Buses] ]
NASA space shuttleover 8.5 minutes consumes 1,000,000 kg of solid propellant (containing 16% aluminum fuel) and 2,000,000 litres of liquid propellant (106,261 kg of liquid hydrogenfuel) to take the 100,000 kg vehicle (including the 25,000 kg payload) to an altitude of 111 km and an orbital velocityof 30,000 km/h. With an energy density of 31MJ per kg for aluminum and 143 MJ/kg for liquid hydrogen, this means that the vehicle starts with 5 TJ of solid propellant and 15 TJ of hydrogen fuel.
* In orbit, at 200 km the vehicle moves at about 7.8 km/s and hence has a kinetic energy of about 3 TJ and a potential energy of roughly 200 GJ. Given the initial energy of 20 TJ, the Space Shuttle is about 16% energy efficient at launching the orbiter and payload, about 4% if just the payload is considered.
* In terms of distance, the space shuttle "Atlantis" flew approximately 8 million kilometres on the
STS-115mission, so used 0.125 kg of solid propellant and 0.25 litres of liquid propellant per kilometre (4.2l/100km per astronaut).
* Again for the Shuttle, in relation to the theoretical largest ground distance (antipodal) flight of 20,000 km, usage is 50 kg of solid propellant and 100 litres of liquid propellant per kilometre.
Objects in sufficiently high orbits have almost negligible air drag, and some satellites are still orbiting decades after launch. In general, rocket and space propulsion efficiency is rarely measured in terms of distance, but in terms of
specific impulsewhich gives how much change in momentum (i.e. impulse) can be obtained from a unit of propellant.
International transport comparisons
UK Public transport
Rail and bus are generally required to serve 'off peak' and rural services, which by their nature have lower loads than city bus routes and inter city train lines. Moreover, due to their 'walk on' ticketing it is much harder to match daily demand and passenger numbers. As a consequence, the overall load factor on UK railways is 33% or 90 people per train [ [http://www.atoc-comms.org/dynamic/publication.php?publication=6] ATOC ] :
Conversely, Air services work on point-to-point networks between large population centres and are 'pre-book' in nature. Using
Yield managementoverall loads can be raised to around 70-90%. However, recently intercity train operators have been using similar techniques, with loads reaching typically 71% overall for TGVservices in France and a similar figure for the UK's Virgin trainsservices. [ [http://www.dft.gov.uk/about/strategy/whitepapers/whitepapercm7176/ Delivering a sustainable railway White paper, p43] ]
For emmisions, the electricity generating source needs to be taken into account. Up to date figures for the UK can be found here:
US Passenger transportation
The US Transportation Energy Data Book states the following figures forPassenger transportation in 2006:cite web
title = Transportation Energy Data Book
publisher = U.S. Department of Energy
date = June 2008
url = http://cta.ornl.gov/data/download27.shtml
accessdate = 2008-07-16]
US Freight transportation
The US Transportation Energy book states the following figures for Freight transportation in 2004: [ [http://yosemite.epa.gov/gw/StatePolicyActions.nsf/uniqueKeyLookup/MSTY5Q4MSV?OpenDocumentUS Environmental protection, 2006] ] [ [http://www.eia.doe.gov/emeu/efficiency/ee_ch5.htm EIA] ]
Corporate Average Fuel Economy(CAFE)
Carbon dioxide equivalentand emission standard
Fuel economy in automobiles
Gasoline gallon equivalent
* ECCM Study for rail, road and air journeys between main UK cities [http://www.businesstravelshow.com/ExhibitorLibrary/127/VirginTrainsEmissionsComparison.pdf]
* [http://www.cheap-parking.net/flight-carbon-emissions.php Flight Emission Calculator]
* [http://www.engineering.lancs.ac.uk/research/download/Transport%20Energy%20Consumption%20Discussion%20Paper.pdf Transport Energy Consumption Discussion Paper 2004 - Prof. Roger Kemp]
* [http://www.rssb.co.uk/pdf/reports/research/T618_traction-summary-rpt_final.pdf Traction Summary Report 2007- Prof. Roger Kemp]
* [http://cta.ornl.gov/data/Index.shtml Transportation Energy Data Book] (U.S.)
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