Fuel efficiency in transportation

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.

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Data

Electric motors are often used to drive vehicles because they can be finely controlled, they deliver power efficiently and they are mechanically very simple. Electric motors often achieve 90% conversion efficiency over the full range of speeds and power output and can be precisely controlled. Electric motors can provide high torque while an EV is stopped, unlike internal combustion engines, and do not need gears to match power curves. This removes the need for gearboxes and torque converters. Electric motors also have the ability to convert movement energy back into electricity, through regenerative braking. This can be used to reduce the wear on brake systems and reduce the total energy requirement of a trip. Electric motors also do not produce greenhouse gases unless, of course, the source of electricity for the motor, such as a coal power plant, produces greenhouse gases.

In most developed countries, most of the electricity does come from fossil-fuelled power plants. These are typically 35-40% efficient. So exercise caution when comparing, say, liquid-fuelled cars to electric trains (or to electric cars). The energy consumption quoted for the electric train (or the electric car) often excludes all the generation losses.

Humans

See also: Human-powered transport

• Walking or running one kilometre requires approximately 70 kcal or 330 kJ of food energy ^[17]. This equates to about 1 L/100 km or 235 mpg in terms of gasoline energy.
• Cycling requires about 120 kJ per km^[17] which equates to approximately 0.36 L/100 km or 653 miles per gallon.

It should be noted, however, that the actual fuel efficiency of human power is in dispute. Recent articles have pointed out that "human power" should include the cost of food production, which can be quite high for energy-intensive diets. ^[18]. The claims by Chris Goodall suggest that walking consumes about the same amount of fuel as driving in some societies, thus the posted human-power efficiencies may be inflated by up to an order of magnitude. It should also be noted that passengers using other modes of transportation also consume food. And, not necessarily less food than those using human power. This brings into question the validity of including food production energy costs in human power efficiency calculations.

Automobiles

Main article: Fuel economy in automobiles

See also: Fuel economy-maximizing behaviors

• We assume 1.3 passengers per car^[19], 114,100 BTU per gallon of unleaded gasoline^[20].
• Honda Insight is rated 70 mpg highway (3.4 l/100km)
• Toyota Prius is rated 59 mpg highway. (3.9 l/100km) ^[21]
• The General Motors EV1 was rated 168 Wh/mile at 60 mph or, at 125,000 Btu/gal 218 mpg (1 l/100km) or 436 passenger-miles/gal (0.63 l/100km).^[22]
• The four passenger GEM NER also uses 169 Wh/mile^[23], which equates to 867 passenger-miles/gal (0.27 l/100km), albeit at only 24 mph. 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 vehicle which gets 27 mile/gge (Gasoline Gallon Equivalent) is actually getting only about 16 mpg (14 l/100km).^[24]

Airplanes

Passenger airplanes averaged 4.8 L/100 km per passenger (1.4 MJ/passenger-km) (49 passenger-miles per gallon) in 1998. Efficiencies around 3 L/100 km per passenger are reached by some carriers. ^[9]. 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. ^[25]

The Sikorsky S-76C++ twin turbine helicopter gets about 1.65 mpg at 140 kts and carries 12 for about 19.8 passenger-miles/gal.^[21]

Ships

The RMS Queen Elizabeth 2 gets 49.5 feet per gallon, or 0.009375 mpg. At 1770 passengers^[26] or 18 passenger-miles per gallon (25,000 L/100 km or 13 L/100 km per passenger (3.8 MJ/passenger-km)).^{[citation needed]}

Trains

• Freight: the AAR claims an energy efficiency of over 400 short ton-miles per gallon of diesel fuel in 2004^[27] (0.588 L/100 km per tonne or 235 J/(km·kg))
• The East Japan Railway Company claims for 2004 an energy intensity of 20.6 MJ/car-km, or about 0.35 MJ/passenger-km^[28]
• a 1997 EC study^[29] 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 ^[30] this is 0.15 MJ/passenger-km, or 506 passenger-mpg in gasoline energy equivalent.
• 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 19Kwh/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. ^[31]
• 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.^[32]
• 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% filled the efficiency would be 328 passenger-mpg. This latter figure translates to 0.27 MJ/passenger-km.^[33]
• 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^[34] and that Japanese trains have a larger number of passengers per car. ^[35]
• Modern electric trains like the shinkansen use regenerative braking to 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.^{[citation needed]}
• This Swiss Railroad company SBB-CFF-FFS cites 0.082 kWh per passenger-km for traction, which is equivalent to 279 MPG ^[36]
• 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^[37], or 39 passenger-miles per gallon

Buses

• 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, or 0.34 MJ/passenger-km.^[38]

Rockets

The NASA space shuttle consumes 1,000,000 kg of solid fuel and 2,000,000 litres of liquid fuel over 8.5 minutes 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. The space shuttle Atlantis flew approximately 8 million km on the STS-115 mission, so used 0.125 kg of solid fuel and 0.25 l of liquid fuel per km. In relation to the largest ground distance of 20,000 km, usage is 50 kg of solid fuel and 100 l of liquid fuel per km.

Nationwide transport comparisons

UK Public transport

The UK DfT state the following figures for public transport in 2005 ^[39]:

The Figures above are derived from the average load which is calculated from the total seats available and the actual passenger numbers.

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 ^[40]:

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. ^[41]

For those wishing to reduce environmentally damaging emissions it is nearly always better to take scheduled public transport services, using up a free seat with virtually zero additional fuel consumption and pollution.

UK Transport vehicle comparison

Note:

* Some trains are equipped with regenerative braking which can save a further 20% of energy.

** Plane fuel consumption is based on the average figures, in reality there is greater fuel consumption initially due to the increased weight in fuel yet to be burnt off.

US Passenger transportation

The US Transportation Energy Data Book states the following figures for Passenger transportation in 2004: ^[53]

US Freight transportation

The US Transportation Energy book states the following figures for Freight transportation in 2004: ^{[53] [54] [55]}

• An independent compilation of real-world efficiency statistics, with references, can be found at strickland.ca/efficiency.html. The author welcomes further substantiated data references.

• ECCM Study for rail, road and air journeys between main UK cities [12]

There is also a growing movement of drivers who practice ways to increase their MPG and save fuel through driving techniques. They are often referred to as hypermilers. Hypermilers have broken records of fuel efficiency, averaging 109 miles per gallon driving a Prius. In non-hybrid vehicles these techniques are also beneficial. Hypermiler Wanye Gerdes can get 59 MPG in a Honda Accord and 30 MPG in an Acura MDX.^[56]

See also

• ACEA agreement
• Alternative propulsion
• Corporate Average Fuel Economy (CAFE)
• Carbon dioxide equivalent and emission standard
• Fuel economy in automobiles
• Fuel efficiency
• Gas-guzzler
• Low-energy vehicle
• Vehicle effiency
• Flight Emission Calculator
• Transport Energy Consumption Discussion Paper 2004 - Prof. Roger Kemp
• Traction Summary Report 2007- Prof. Roger Kemp