Energy efficiency in transportation
| Aircraft | Concorde | Boeing 747-400 |
|---|---|---|
| Passenger-miles/imperial gallon | 17 | 109 |
| Passenger-miles/US gallon | 14 | 91 |
| Litres/100 passenger-km | 16.6 | 3.1 |
Energy efficiency in transportation is, strictly speaking, useful output (kilometers, miles, etc.) divided by total energy input (kilowatt-hour, amount of gasoline, etc.). This is more precisely known as fuel economy (symbol FE), and commonly measured in units of km/L or mi/gal (MPG).
Energy efficiency in transportation is often (and confusingly) described in terms of fuel consumption (symbol FC). Fuel consumption is the reciprocal of fuel economy and is occasionally known as energy intensity; it equals fuel (energy) divided by distance, and is often measured in units of liters per 100 kilometers (L/100 km), joules per kilometer (J/km), gallon-equivalent per 100 miles (gale/100 mi), or kilowatt-hours per distance (kW-hr/km or kW-hr/mi).
The energy efficiency in transportation varies by mode of transportation (listed below). Different types of transportation range from some hundred kilojoules per kilometre (kJ/km) for a bicycle to tens of megajoules per kilometer (MJ/km) for a helicopter.
Both fuel economy and fuel consumption are often given on a per-vehicle basis. More refined units of measurement exist, such as fuel consumption per passenger or fuel consumption per mass of cargo.
Energy efficiency is expressed in terms of fuel economy:
Energy intensity (reciprocal efficiency) is expressed terms of fuel consumption:
For freight transport, rail and ship transport are generally much more efficient than trucking, and air freight is much less efficient.
A 68 kg (150 lb) person walking at 4 km/h (2.5 mph) requires approximately 210 kilocalories (880 kJ) of food energy per hour, which is equivalent to 4.55 km/MJ. 1 US gal (3.8 L) of gasoline contains about 114,000 British thermal units (120 MJ) of energy, so this is approximately equivalent to 360 miles per US gallon (0.65 L/100 km).
Velomobiles have the highest energy efficiency of any known mode of personal transportation. At a speed of 50 km/h (31 mph), the velomobile manufacturer WAW claims that only 0.5 kW·h of food energy per 100 km is needed to transport the passenger, which is around 1⁄5 (20%) of what is needed to power a standard upright bicycle, and 1⁄50 (2%) of that which is consumed by an average fossil fuel or electric car. This corresponds to 4700 miles per US gallon (2000 km/L, 0.05 L/100 km). Other sources give a figure of 1⁄3.4 (29.5%) of the energy use of a normal bicycle.
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