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.

Contents

[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 unlike journeys an airline jet cannot be used for an urban commute thus when comparing aircraft with cars the car figures must eliminate the effect of urban commuting
  • There is currently no agreed upon method of comparing electric vehicle efficiency to heat engine (fossil fuel) vehicle efficiency. However where the issue is climate change the emissions can be compared. If the issue is investment in new electric mass transit it is important to use emissions associate with the most polluting fuel because increased demand for electricity increases the use of the most polluting fuel used in generation for the foreseeable 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 inherantly a small proportion of vehicle kilometres see Transport Energy Metrics, Lessons fron the west Coast Main line Modernisation and figures for London Underground in transport statistics for Great Britain 2003. Lessons from the west coast mainainline modernisation suggest that long passenger rail should operate st 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. In considering investment to reduce the climate change 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.[1]
  • 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 eficiency in tranpsortation in the context of impact on climate change

[edit] Transportation modes

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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).

[edit] Automobiles

Main article: Fuel economy in automobiles
See also: Fuel economy-maximizing behaviors
  • 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.[3]
  • In 2006, the average occupancy for cars in the UK was 1.58.[4]
  • 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.[5]
  • Honda Insight was rated 70 mpg–U.S. (3.36 L/100 km / 84.1 mpg–imp) highway.[citation needed]
  • Toyota Prius - According to the U.S. EPA's revised estimates, the combined fuel consumption for the 2008 Prius is 46 mpg–U.S. (5.11 L/100 km / 55.2 mpg–imp),[9] making it the most fuel efficient U.S. car of 2008.[10] In the UK, the official fuel consumption figure (combined) for the Prius is 4.3 L/100 km (55 mpg–U.S. / 66 mpg–imp).[11]
  • The General Motors EV1 was rated in a test with a charging efficiency of 373 Wh-AC/mile or 0.6 kWh/100 km .[12]
  • The four passenger GEM NER also uses 169 Wh/mile or 0.3 kWh/100 km ,[13] which equates to 0.1 kWh/100 km for four passengers, albeit at only 24 mph (39 km/h).
  • Since hydrogen is 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 vehicle which gets 8.7 L/100 km (27 MPGeUS) is actually getting only about 14.7 L/100 km (16 MPGeUS).[14]

[edit] Aircraft

  • Airbus state that their A380 consumes fuel at the rate of less than 3 L/100 km per passenger.[15] 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.[16] 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.[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. [17]
  • 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.[18]

[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.[19] 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[20] (0.588 L/100 km per tonne or 235 J/(km·kg))
  • a 1997 EC study[22] 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 [23] 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. [24]
  • 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.[25]
  • 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, 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.[26]
  • 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[27] and that Japanese trains have a larger number of passengers per car. [28]
  • This Swiss Railroad company SBB-CFF-FFS cites 0.082 kWh per passenger-km for traction.[29]
  • 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[30], 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." [31] 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.[32]
  • The fleet of 244 1982 New Flyer 40 foot 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.[33]

[edit] Rockets

  • The NASA space shuttle over 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 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. 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] 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 33% or 90 people per train [34]:

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. [35]

For emmisions, 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

[edit] US Passenger transportation

The US Transportation Energy Data Book states the following figures for Passenger transportation in 2004: [36]

Transport mode Average passengers
per vehicle		 Efficiency
per passenger
Vanpool 6.4 1,294 BTU/mi 2.6 L/100 km (89 MPGeUS)
Motorcycles 1.1 2,272 BTU/mi 4.6 L/100 km (51 MPGeUS)
Rail (Commuter) 32.9 2,569 BTU/mi 5.3 L/100 km (45 MPGeUS)
Rail (Transit Light & Heavy) 22.4 2,750 BTU/mi 5.6 L/100 km (42 MPGeUS)
Rail (Intercity Amtrak) 17.9 2,760 BTU/mi 5.6 L/100 km (42 MPGeUS)
Cars 1.57 3,496 BTU/mi 7.2 L/100 km (33 MPGeUS)
Air 90.4 3,959 BTU/mi 8.1 L/100 km (29 MPGeUS)
Buses (Transit) 8.7 4,318 BTU/mi 8.8 L/100 km (27 MPGeUS)
Personal Trucks 1.72 4,329 BTU/mi 8.9 L/100 km (27 MPGeUS)

[edit] US Freight transportation

The US Transportation Energy book states the following figures for Freight transportation in 2004: [36] [37] [38]

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] Footnotes

  1. ^ Newman, Peter; Jeffrey R. Kenworthy (1999). Sustainability and Cities: Overcoming Automobile Dependence. Island Press. ISBN 1559636602. 
  2. ^ a b Energy expenditure for walking and running
  3. ^ MTC - Maps and Data
  4. ^ Transport trends: current edition. UK Department for Transport (2008-01-08). Retrieved on 2008-03-23.
  5. ^ Oak Ridge National Laboratory (ORNL)
  6. ^ Best on CO2 rankings. UK Department for Transport. Retrieved on 2008-03-22.
  7. ^ 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. Retrieved on 2008-03-22.
  8. ^ Vehicle details for Ibiza ( from NOV 06 Wk 45 > ) 1.4 TDI 80PS Ecomotion M5. UK Vehicle Certification Agency. Retrieved on 2008-03-22.
  9. ^ 2008 Toyota Prius. EPA. Retrieved on 2007-12-25.
  10. ^ 2008 Most and Least Fuel Efficient Vehicles (ranked by city mpg). United States Environmental Protection Agency and United States Department of Energy. Retrieved on 2007-12-25.
  11. ^ Vehicle details for Prius 1.5 VVT-i Hybrid E-CVT. UK Vehicle Certification Agency. Retrieved on 2008-03-22.
  12. ^ http://www1.eere.energy.gov/vehiclesandfuels/avta/pdfs/fsev/eva_results/ev1_eva.pdf
  13. ^ NEV America U.S. Dept. of Energy Field Operations Program - 2005 Global Electronic Motorcars e4 4-Passenger
  14. ^ Hydrogen Internal Combustion Engine (ICE) Vehicle Testing Activities
  15. ^ The A380: The future of flying. Airbus. Retrieved on 2008-03-22.
  16. ^ Matthew Knight. "Green light for the new A380", CNN.com, Cable News Network, 2007-10-26. Retrieved on 2008-03-23. 
  17. ^ National Aerospace Laboratory
  18. ^ Ecogeek Article
  19. ^ Queen Elizabeth 2: Technical Information. Cunard Line. Retrieved on 2008-03-31.
  20. ^ Railroads: Building a Cleaner Environment, Association of American Railroads
  21. ^ Environmental Goals and Results, JR-East Sustainability Report 2005
  22. ^ Estimating Emissions from Railway Traffic
  23. ^ European Environment Agency Occupancy Rates, page 3
  24. ^ Commission for integrated transport, Short haul air v High speed rail
  25. ^ Combino - Low Floor Light Rail Vehicles Tests, Trials and Tangible Results
  26. ^ Colorado Railcar: "DMU Performs Flawlessly on Tri-Rail Service Test"
  27. ^ Fuel Efficiency of Travel in the 20th Century, Appendix
  28. ^ Fuel Efficiency of Travel in the 20th Century
  29. ^ SBB Environmental Report 2002/2003
  30. ^ Amtrak - Inside Amtrak - News & Media - Energy Efficient Travel
  31. ^ Bus and Rail Final Report
  32. ^ Passenger Transport (Fuel Consumption). Hansard. UK House of Commons (2005-07-20). Retrieved on 2008-03-25.
  33. ^ Demonstration of Caterpillar C-10 Duel-Fuel Engines in MCI 102DL3 Commuter Buses
  34. ^ [1] ATOC
  35. ^ Delivering a sustainable railway White paper, p43
  36. ^ a b [http://cta.ornl.gov/data/tedb26/Edition26_Chapter02.pdf Transportation Energy Data Book, 2007]
  37. ^ [http://yosemite.epa.gov/gw/StatePolicyActions.nsf/uniqueKeyLookup/MSTY5Q4MSV?OpenDocument US Environmental protection, 2006]
  38. ^ EIA

[edit] See also

[edit] External links