Fuel economy in automobiles

The fuel economy or fuel efficiency of an automobile relates to the distance traveled by a vehicle and the amount of fuel consumed. It can be expressed in terms of the volume of fuel to travel a given distance, such as in litres per 100 kilometres, or through its inverse, the distance traveled per unit volume of fuel consumed, as in kilometres per litre or miles per gallon. Since fuel economy of vehicles is a significant factor in air pollution, the importation of motor fuel can be a large part of a nation's foreign trade and consumers frequently undervalue fuel efficiency, many countries impose requirements for fuel economy.
Different methods are used to approximate the actual performance of the vehicle. The energy in fuel is required to overcome various losses encountered while propelling the vehicle, and in providing power to vehicle systems such as ignition or air conditioning. Various strategies can be employed to reduce losses at each of the conversions between the chemical energy in the fuel and the kinetic energy of the vehicle. Driver behavior can affect fuel economy; maneuvers such as sudden acceleration and heavy braking waste energy.
Electric cars use kilowatt-hours of electricity per 100 kilometres ; in the U.S., an equivalence measure, such as miles per gallon gasoline equivalent has been created to attempt to compare them.

Quantities and units of measure

The fuel efficiency of motor vehicles can be expressed in multiple ways:

Fuel consumption is the fuel used per unit distance; for example, litres per 100 kilometres . The lower the value, the more economic a vehicle is; this is the measure generally used across Europe, Africa, New Zealand, Australia, and Canada, Uruguay, Paraguay, Guatemala, Colombia, China, and Madagascar, and in the former CIS states.,
Fuel economy is the distance travelled per unit volume of fuel used; for example, kilometres per litre or miles per gallon . The higher the value, the more economic a vehicle is. This measure is popular in the US and the UK, but in Europe, India, Japan, South Korea the metric unit km/L is used instead.

The formula for converting to miles per US gallon from L/100 km is, where is value of L/100 km. For miles per Imperial gallon the formula is.
Europe now uses the WLTP standard to compare the fuel economy of all new vehicles.
Fuel economy can be expressed in two ways:
;Units of fuel per fixed distance:Generally expressed in liters per 100 kilometers, used in most European countries, Canada, China, South Africa, Australia and New Zealand. Irish law allows for the use of miles per imperial gallon, alongside liters per 100 kilometers. Liters per 100 kilometers may be used alongside miles per imperial gallon in the UK. The window sticker on new US cars displays the vehicle's fuel consumption in US gallons per 100 miles, in addition to the traditional mpg number. A lower number means more efficient, while a higher number means less efficient.
;Units of distance per fixed fuel unit: Miles per gallon are commonly used in the United States, the United Kingdom, and Canada. Kilometers per liter are more commonly used elsewhere in the Americas, Asia, parts of Africa and Oceania. In the Levant km/20 L is used, known as kilometers per tanaka, a metal container which has a volume of twenty liters. When mpg is used, it is necessary to identify the type of gallon: the imperial gallon is 4.54609 liters, and the U.S. gallon is 3.785 liters. When using a measure expressed as distance per fuel unit, a higher number means more efficient, while a lower number means less efficient.
'''Conversions of units:'''

Statistics

While the thermal efficiency of petroleum engines has increased since the beginning of the automotive era, this is not the only factor in fuel economy. The design of automobile as a whole and usage pattern affects the fuel economy. Published fuel economy is subject to variation between jurisdiction due to variations in testing protocols.
One of the first studies to determine fuel economy in the United States was the Mobil Economy Run, which was an event that took place every year from 1936 to 1968. It was designed to provide real, efficient fuel efficiency numbers during a coast-to-coast test on real roads and with regular traffic and weather conditions. The Mobil Oil Corporation sponsored it and the United States Auto Club sanctioned and operated the run. In more recent studies, the average fuel economy for new passenger car in the United States improved from 17 mpg in 1978 to 22 mpg in 1982.
The average fuel economy for new 2020 model year cars, light trucks and SUVs in the United States was. 2019 model year cars classified as "midsize" by the US EPA ranged from 12 to 56 mpg_US However, due to environmental concerns caused by CO₂ emissions, new EU regulations are being introduced to reduce the average emissions of cars sold beginning in 2012, to 130 g/km of CO₂, equivalent to 4.5 L/100 km for a diesel-fueled car, and 5.0 L/100 km for a gasoline -fueled car.
The average consumption across the fleet is not immediately affected by the new vehicle fuel economy: for example, Australia's car fleet average in 2004 was 11.5 L/100 km, compared with the average new car consumption in the same year of 9.3 L/100 km

Speed and fuel economy studies

Fuel economy at steady speeds with selected vehicles was studied in 2010. The most recent study indicates greater fuel efficiency at higher speeds than earlier studies; for example, some vehicles achieve better fuel economy at rather than at, although not their best economy, such as the 1994 Oldsmobile Cutlass Ciera with the LN2 2.2L engine, which has its best economy at , and gets better economy at than at . The proportion of driving on high speed roadways varies from 4% in Ireland to 41% in the Netherlands.
When the US National Maximum Speed Law's speed limit was mandated from 1974 to 1995, there were complaints that fuel economy could decrease instead of increase. The 1997 Toyota Celica got better fuel-efficiency at than it did at , although even better at than at , and its best economy at only. Other vehicles tested had from 1.4 to 20.2% better fuel-efficiency at vs.. Their best economy was reached at speeds of .
Officials hoped that the limit, combined with a ban on ornamental lighting, no gasoline sales on Sunday, and a 15% cut in gasoline production, would reduce total gasoline consumption by 200,000 barrels a day, representing a 2.2% drop from annualized 1973 gasoline consumption levels. This was partly based on a belief that cars achieve maximum efficiency between 40 and 50 mph and that trucks and buses were most efficient at.
In 1998, the U.S. Transportation Research Board footnoted an estimate that the 1974 National Maximum Speed Limit reduced fuel consumption by 0.2 to 1.0 percent. Rural interstates, the roads most visibly affected by the NMSL, accounted for 9.5% of the U.S' vehicle-miles-traveled in 1973, but such free-flowing roads typically provide more fuel-efficient travel than conventional roads.

Discussion of statistics

A reasonably modern European supermini and many mid-size cars, including station wagons, may manage motorway travel at or, with carbon dioxide emissions of around 140 g/km.
An average North American mid-size car averages ) city, ) highway; a full-size SUV usually averages city and highway. Pickup trucks vary considerably; whereas a 4 cylinder-engined light pickup can achieve, a V8 full-size pickup with extended cabin averages city and highway.
The average fuel economy for all vehicles on the road is higher in Europe than the United States because the higher cost of fuel changes consumer behaviour. In the UK, an imperial gallon of fuel cost US$6.06 in 2005. The average cost in the United States was US$2.61 for a US gallon.
European-built cars are generally more fuel-efficient than US vehicles. While Europe has many highly efficiency diesel cars, European gasoline/petrol vehicles are on average also more efficient than gasoline-powered vehicles in the USA. Most European vehicles cited in the CSI study run on diesel engines, which tend to achieve greater fuel efficiency than gasoline/petrol engines. Selling those cars in the United States is difficult because of emission standards, notes Walter McManus, a fuel economy expert at the University of Michigan Transportation Research Institute. "For the most part, European diesels don’t meet U.S. emission standards", McManus said in 2007. Another reason why many European models are not sold in the United States is that labor unions object to having the big 3 import any new foreign built models regardless of fuel economy while laying off workers at home.
An example of European cars' capabilities of fuel economy is the microcar Smart Fortwo cdi, which can achieve up to using a turbocharged three-cylinder
Diesel engine. The Fortwo is produced by Daimler AG and is only sold by one company in the United States. Furthermore, the world record in fuel economy of production cars is held by the Volkswagen Group, with special production models of the Volkswagen Lupo and the Audi A2, consuming as little as.
Diesel engines generally achieve greater fuel efficiency than petrol engines. Passenger car diesel engines have energy efficiency of up to 41% but more typically 30%, and petrol engines of up to 37.3%, but more typically 20%. A common margin is 25% more efficiency for a turbodiesel.
For example, the current model Skoda Octavia, using Volkswagen engines, has a combined European fuel efficiency of for the petrol engine and for the heavier diesel engine vehicle. The higher compression ratio raises the energy efficiency, but diesel fuel also contains approximately 10% more energy per unit volume than gasoline/petrol which contributes to the reduced fuel consumption for a given power output.
In 2002, the United States had 85,174,776 trucks, and averaged. Large trucks, over, averaged.

GVWR lbs	Number	Percentage	Average miles per truck	fuel economy	Percentage of fuel use
6,000 lbs and less	51,941,389	61.00%	11,882	17.6	42.70%
6,001 – 10,000 lbs	28,041,234	32.90%	12,684	14.3	30.50%
Light truck subtotal	79,982,623	93.90%	12,163	16.2	73.20%
10,001 – 14,000 lbs	691,342	0.80%	14,094	10.5	1.10%
14,001 – 16,000 lbs	290,980	0.30%	15,441	8.5	0.50%
16,001 – 19,500 lbs	166,472	0.20%	11,645	7.9	0.30%
19,501 – 26,000 lbs	1,709,574	2.00%	12,671	7	3.20%
Medium truck subtotal	2,858,368	3.40%	13,237	8	5.20%
26,001 – 33,000 lbs	179,790	0.20%	30,708	6.4	0.90%
33,001 lbs and up	2,153,996	2.50%	45,739	5.7	20.70%
Heavy truck subtotal	2,333,786	2.70%	44,581	5.8	21.60%
Total	85,174,776	100.00%	13,088	13.5	100.00%

The average economy of automobiles in the United States in 2002 was. By 2010 this had increased to. Average fuel economy in the United States gradually declined until 1973, when it reached a low of and gradually has increased since, as a result of higher fuel cost. A study indicates that a 10% increase in gas prices will eventually produce a 2.04% increase in fuel economy. One method by car makers to increase fuel efficiency is lightweighting in which lighter-weight materials are substituted in for improved engine performance and handling.