Fuel efficiency in transportation

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This page describes fuel efficiency in means of transportation. For the environmental impact assessment of a given product or service throughout its lifespan, see life cycle assessment.

The fuel efficiency in transportation ranges from a low of a few miles per gallon (less than a kilometer per liter) for a helicopter to a high of several hundred miles per gallon (a few hundred kilometers per liter) for a bicycle. Also included, but not directly comparable, are rockets, which, since they can coast with little friction in space, get both the highest and lowest fuel efficiency, by far.

Contents

[edit] Transportation modes

For freight transport, rail and ship transport are generally much more efficient than trucking, and air freight is much less efficient. (See graph[1])

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[edit] Walking

  • Walking or running one kilometre requires approximately 70 kcal or 330 kJ of food energy [2]. This equates to about 1 L/100 km (235 MPGeUS) in terms of gasoline energy.

[edit] Bicycling

  • Cycling requires about 120 kJ per km[2] which equates to approximately 0.4 L/100 km (653 MPGeUS). A motorized bicycle such as the Velosolex affords the rider to cycle under human power or with the assistance of a 49cc clean burning engine which equates to a range of 160-200 MPG (1.4L/100Km).

[edit] Automobiles

Main article: Fuel economy in automobiles
See also: Fuel economy-maximizing behaviors

Automobile fuel efficiency is often expressed in distance per volume fuel consumed (i.e., miles per gallon). This is complicated by the different energy content of fuels (compare petrol and diesel). 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 compared to 130,500 BTU or 36.4 MJ/L for diesel. [3] A second important consideration is the energy costs of producing these fuels - bio-fuels, electricity and hydrogen, for instance, have significant energy inputs in their products. Because of this, the 50-70% efficiency of hydrogen production has to be combined with the vehicle efficiency to yield net efficiency. Thus a hydrogen vehicle getting 8.7 L/100 km (27 MPGeUS) has an efficiency net of energy production costs of 14.7 L/100 km (16 MPGeUS) or around 60% of vehicle efficency [4].

Efficiency can also be expressed in terms of consumption per passenger mile or in weight of cargo transported. These values impact heavily on obtained efficiency. For instance, the Metropolitan Transport Commission for the nine-county San Francisco Bay Area estimates an automobile occupancy rate of about 1.3 passengers per car.[5], and in 2006, average occupancy in the UK was estimated at 1.58.[6]. Increases in passenger number increase consumption per mile only slightly, compared to the effect on passenger miles.

[edit] Example consumption figures

  • Honda Insight was rated 70 miles per US gallon (3.4 L/100 km; 84 mpg-imp) highway.[citation needed]
  • 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 46 miles per US gallon (5.1 L/100 km; 55 mpg-imp),[10] making it the most fuel efficient U.S. car of 2008.[11] In the UK, the official fuel consumption figure (combined) for the Prius is 4.3 litres per 100 kilometres (66 mpg-imp; 55 mpg-US).[12]
  • The General Motors EV1 was rated in a test with a charging efficiency of 373 Wh-AC/mile or 0.6 kWh/100 km .[13]
  • The four passenger GEM NER also uses 169 Wh/mile or 0.3 kWh/100 km ,[14] which equates to 0.1 kWh/100 km for four passengers, albeit at only 24 mph (39 km/h).

[edit] Aircraft

A principle determinant of fuel consumption in aircraft is drag, which must be opposed by thrust for the aircraft to progress. Drag increases approximately as the square of lift required for flight[15], and, as force of lift is directly related to craft weight, to aircraft weight2. Unlike parasitic or form drag, induced drag decreases with the square of velocity, making flight at higher-speeds more efficient (see drag).

As induced drag increases as a power function of weight, mass reduction, along with improvements in engine efficiency and reductions in aerodynamic drag, has been a principle source of efficiency gains in craft, with a rule-of-thumb being that a 1% weight reduction corresponds to around a .75% reduction in fuel consumption.[15] Altitude impacts on both air-drag and engine efficiency, the altitude at which aircraft are permitted to fly greatly influences their fuel consumption. Jet-engine cruising efficiency increases at altitude due to the constraint to maintain a combustible fuel mixture: low-pressure air allows reduced fuel injection while maintaining an adequate fuel:air ratio.[15]

Passenger airplanes averaged 4.8 L/100 km per passenger (1.4 MJ/passenger-km) (49 passenger-miles per gallon) in 1998.[citation needed] 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. [16] As over 80% of the fully-laden take-off weight of a modern aircraft such as the Airbus A380 is craft and fuel, there remains considerable room for future improvements in efficiency.

  • Airbus state that their A380 consumes fuel at the rate of less than 3 L/100 km per passenger.[17] 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.[18] Typical occupancy figures are unknown at this time. Furthermore, the A380, unlike other airliners, has special dispensation from the FAA to fly higher than 40,000 feet (12,000 m).[19]
  • NASA and Boeing are conducting tests on a 500 lb (230 kg). "blended wing" aircraft. This design allows for greater fuel efficiency since the whole craft produces lift, not just the wings.[20]
  • The Bell 407 single engine turbine helicopter burns 51 gallons per hour at 120 knots carrying 1 pilot and 6 passengers. 2.35 NM per Gal for 14.1 passenger-miles per gallon. If the pilot wants to go the same place it's 16.4 people-miles per gallon. Increased altitudes can yield better fuel rates. I have seen it perform down to 47 gal/hr, and if you can find a more helpful tailwind at altitude than the surface winds, you can burn less fuel per hour and make greater ground speeds.

[edit] Ships

  • Cunard state that their liner, the RMS Queen Elizabeth 2, travels 49.5 ft (15.1 m) per 1 imperial gallon (4.546 l) of diesel oil, and that it has a passenger capacity of 1777.[21] From those figures, fuel consumption can be calculated as 0.009375 miles per imperial gallon (30,130 L/100 km). Carrying 1777 passengers, that equates to 16.7 miles per imperial gallon (16.9 L/100 km) per passenger.

[edit] Trains

  • Freight: the AAR claims an energy efficiency of over 400 short ton-miles per gallon of diesel fuel in 2004[22] (0.588 L/100 km per tonne or 235 J/(km·kg))
  • a 1997 EC study[24] on page 74 claims 18.00 kWh/train-km for the TGV Duplex assuming 3 intermediate stops between Paris and Lyon. This equates to 64.80 MJ/train-km. With 80% of the 545 seats filled on average [25] 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 TGV double-deck ‘Duplex’ trains use lightweight materials in order to keep axle loads down and reduce damage to track, this saves considerable energy. [26]
  • A Siemens study of Combino light rail vehicles in service in Basel, Switzerland over 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.[27]
  • A trial of a Colorado Railcar double-deck DMU hauling two Bombardier Bi-level coaches found fuel consumption to be 128 US gallons for 144 miles (232 km), 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%[citation needed] filled the efficiency would be 328 passenger-mpg.[28]
  • 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[29] and that Japanese trains have a larger number of passengers per car. [30]
  • This Swiss Railroad company SBB-CFF-FFS cites 0.082 kWh per passenger-km for traction.[31]
  • AEA carried out a detailed study of road and rail for the United Kingdom Department for Transport. Final report
  • Amtrak reports 2005 energy use of 2,935 BTU per passenger-mile[32], 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." [33] Having to accelerate and decelerate a heavy train load of people at every stop is inefficient despite regenerative braking which can recover typically around 20% of the energy wasted in braking.

[edit] Buses

  • In July 2005, the average occupancy for buses in the UK was stated to be 9.[34]
  • The fleet of 244 1982 New Flyer 40-foot (12 m) trolley buses in local service with BC Transit in 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.[35]

[edit] Rockets

  • The NASA space shuttle over 8.5 minutes consumes 1,000,000 kg of solid propellant (containing 16% aluminium fuel) and 2,000,000 litres of liquid propellant (106,261 kg of liquid hydrogen fuel) to take the 100,000 kg vehicle (including the 25,000 kg payload) to an altitude of 111 km and an orbital velocity of 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-115 mission, so used 0.125 kg of solid propellant and 0.25 litres of liquid propellant per kilometre (4.2l/100 km 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 impulse which gives how much change in momentum (i.e. impulse) can be obtained from a unit of propellant.

[edit] Other

  • NASA's Crawler-Transporter is used to move the Shuttle from storage to the launch pad. It has one of the the highest fuel consumption rates on record, 150 gallons/mile, which is 32 feet/gallon. [36]


[edit] International transport comparisons

[edit] 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 35% or 90 people per train [37]:

Conversely, Air services work on point-to-point networks between large population centres and are 'pre-book' in nature. Using Yield management overall 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 TGV services in France and a similar figure for the UK's Virgin trains services. [38]

For emissions, the electricity generating source needs to be taken into account. Up to date figures for the UK can be found here:

http://www.atoc-comms.org/admin/userfiles/Energy%20&%20Emissions%20Statement%20-%20web%20version.pdf

http://www.defra.gov.uk/environment/business/envrp/pdf/passenger-transport.pdf

http://www.aef.org.uk/downloads//Grams_CO2_transportmodesUK.pdf

[edit] US Passenger transportation

The US Transportation Energy Data Book states the following figures for Passenger transportation in 2006: [39]

Transport mode Average passengers
per vehicle		 Efficiency
per passenger
Vanpool 6.1 1,322 BTU/mi 2.7 L/100 km (87 MPGeUS)
Motorcycles 1.2 1,855 BTU/mi 3.8 L/100 km (62 MPGeUS)
Rail (Commuter) 31.3 2,996 BTU/mi 6.1 L/100 km (38 MPGeUS)
Rail (Transit Light & Heavy) 22.5 2,784 BTU/mi 5.7 L/100 km (41 MPGeUS)
Rail (Intercity Amtrak) 20.5 2,650 BTU/mi 5.4 L/100 km (43 MPGeUS)
Cars 1.57 3,512 BTU/mi 7.2 L/100 km (33 MPGeUS)
Air 96.2 3,261 BTU/mi 6.7 L/100 km (35 MPGeUS)
Buses (Transit) 8.8 4,235 BTU/mi 8.7 L/100 km (27 MPGeUS)
Personal Trucks 1.72 3,944 BTU/mi 8.1 L/100 km (29 MPGeUS)

[edit] US Freight transportation

The US Transportation Energy book states the following figures for Freight transportation in 2004: [39] [40] [41]

Transportation mode Fuel consumption
BTU per short ton mile kJ per tonne kilometre
Class 1 Railroads 341 246
Domestic Waterbourne 510 370
Heavy Trucks 3,357 2,426
Air freight (aprox) 9,600 6,900

[edit] Caveats


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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.
  • 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 consumption per capita declines sharply as population density increases, since journeys become shorter.[42]
  • 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 [43] [44].

[edit] Footnotes

  1. ^ David Strahan, "Green fuel for the airline industry", New Scientist, 13 Aug. 2008, pp. 34-7.
  2. ^ a b Energy expenditure for walking and running
  3. ^ Oak Ridge National Laboratory (ORNL)
  4. ^ Hydrogen Internal Combustion Engine (ICE) Vehicle Testing Activities
  5. ^ MTC - Maps and Data
  6. ^ "Transport trends: current edition". UK Department for Transport. 2008-01-08. http://www.dft.gov.uk/pgr/statistics/datatablespublications/trends/current/. Retrieved on 2008-03-23. 
  7. ^ "Best on CO2 rankings". UK Department for Transport. http://www.dft.gov.uk/ActOnCO2/index.php?q=best_on_co2_rankings. Retrieved on 2008-03-22. 
  8. ^ "Vehicle details for Polo 3 / 5 Door (from NOV 06 Wk 45>) 1.4 TDI (80PS) (without A/C) with DPF BLUEMOTION M5". UK Vehicle Certification Agency. http://www.vcacarfueldata.org.uk/search/vehicleDetails.asp?id=20690. Retrieved on 2008-03-22. 
  9. ^ "Vehicle details for Ibiza ( from NOV 06 Wk 45 > ) 1.4 TDI 80PS Ecomotion M5". UK Vehicle Certification Agency. http://www.vcacarfueldata.org.uk/search/vehicleDetails.asp?id=20471. Retrieved on 2008-03-22. 
  10. ^ "2008 Toyota Prius". EPA. http://www.fueleconomy.gov/feg/noframes/24882.shtml. Retrieved on 2007-12-25. 
  11. ^ "2008 Most and Least Fuel Efficient Vehicles (ranked by city mpg)". United States Environmental Protection Agency and United States Department of Energy. http://www.fueleconomy.gov/feg/best/bestworstNF.shtml. Retrieved on 2007-12-25. 
  12. ^ "Vehicle details for Prius 1.5 VVT-i Hybrid E-CVT". UK Vehicle Certification Agency. http://www.vcacarfueldata.org.uk/search/vehicleDetails.asp?id=10982. Retrieved on 2008-03-22. 
  13. ^ http://www1.eere.energy.gov/vehiclesandfuels/avta/pdfs/fsev/eva_results/ev1_eva.pdf
  14. ^ NEV America U.S. Dept. of Energy Field Operations Program - 2005 Global Electronic Motorcars e4 4-Passenger
  15. ^ a b c Barney L. Capehart (2007). Encyclopedia of Energy Engineering and Technology, Volume 1. CRC Press. ISBN 0849336538, 9780849336539.
  16. ^ National Aerospace Laboratory
  17. ^ "The A380: The future of flying". Airbus. http://www.airbus.com/en/myairbus/airbusview/the_a380_the_future_of_flying.html. Retrieved on 2008-03-22. 
  18. ^ Matthew Knight (2007-10-26). "Green light for the new A380". CNN.com (Cable News Network). http://www.cnn.com/2007/TECH/10/25/fsummit.climate.A380/index.html. Retrieved on 2008-03-23. 
  19. ^ "Exemption No. 8695". Renton, Washington: Federal Aviation Authority. 2006-03-24. http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgEX.nsf/0/9929ce16709cad0f8625713f00551e74/$FILE/8695.doc. Retrieved on 2008-10-02. 
  20. ^ Ecogeek Article
  21. ^ "Queen Elizabeth 2: Technical Information" (PDF). Cunard Line. http://www.cunard.com/uploads/QE2_Tech.pdf. Retrieved on 2008-03-31. 
  22. ^ Railroads: Building a Cleaner Environment, Association of American Railroads
  23. ^ Environmental Goals and Results, JR-East Sustainability Report 2005
  24. ^ Estimating Emissions from Railway Traffic
  25. ^ European Environment Agency Occupancy Rates, page 3
  26. ^ Commission for integrated transport, Short haul air v High speed rail
  27. ^ Combino - Low Floor Light Rail Vehicles Tests, Trials and Tangible Results
  28. ^ Colorado Railcar: "DMU Performs Flawlessly on Tri-Rail Service Test"
  29. ^ Fuel Efficiency of Travel in the 20th Century, Appendix
  30. ^ Fuel Efficiency of Travel in the 20th Century
  31. ^ SBB Environmental Report 2002/2003
  32. ^ Amtrak - Inside Amtrak - News & Media - Energy Efficient Travel
  33. ^ Bus and Rail Final Report
  34. ^ "Passenger Transport (Fuel Consumption)". Hansard. UK House of Commons. 2005-07-20. http://www.publications.parliament.uk/pa/cm200506/cmhansrd/vo050720/text/50720w26.htm#50720w26.html_sbhd1. Retrieved on 2008-03-25. 
  35. ^ Demonstration of Caterpillar C-10 Duel-Fuel Engines in MCI 102DL3 Commuter Buses
  36. ^ NASA Crawler-Transporter statistics
  37. ^ [1] ATOC
  38. ^ Delivering a sustainable railway White paper, p43
  39. ^ a b Davis, Stacy C.; Susan W. Diegel, Robert G. Boundy (2009). Transportation Energy Data Book: Edition 28. U.S. Department of Energy. pp. Table 2.12. ORNL-6984 (Edition 28 of ORNL-5198). http://cta.ornl.gov/data/. Retrieved on 2009-07-12. 
  40. ^ [http://yosemite.epa.gov/gw/StatePolicyActions.nsf/uniqueKeyLookup/MSTY5Q4MSV?OpenDocument US Environmental protection, 2006]
  41. ^ EIA
  42. ^ Newman, Peter; Jeffrey R. Kenworthy (1999). Sustainability and Cities: Overcoming Automobile Dependence. Island Press. ISBN 1559636602. 
  43. ^ Top 10 Fuel Misers - MSN Autos
  44. ^ Fuel Economy

[edit] See also

[edit] External links

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