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Odd–even rationing is a method of
rationing Rationing is the controlled distribution (marketing), distribution of scarcity, scarce resources, goods, services, or an artificial restriction of demand. Rationing controls the size of the ration, which is one's allowed portion of the resourc ...
in which access to some resource is restricted to some of the population on any given day. In a common example, drivers of private vehicles may be allowed to drive, park, or purchase
gasoline Gasoline ( North American English) or petrol ( Commonwealth English) is a petrochemical product characterized as a transparent, yellowish, and flammable liquid normally used as a fuel for spark-ignited internal combustion engines. When for ...
on alternating days, according to whether the last digit in their
license plate A vehicle registration plate, also known as a number plate (British, Indian and Australian English), license plate (American English) or licence plate (Canadian English), is a metal or plastic plate attached to a motor vehicle or trailer for ...
is even or odd. Similarly, during a
drought A drought is a period of drier-than-normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D.  Jiang, A.  Khan, W.  Pokam Mba, D.  Rosenfeld, J. Tierney, ...
, houses can be restricted from using water outdoors according to the parity of the house number. Typically a day is "odd" or "even" depending on the day of the month. An issue with this approach is that two "odd" days in a row occur whenever a month ends on an odd-numbered day. Sometimes odd or even may be based on
day of the week In a vast number of languages, the names given to the seven days of the week are derived from the names of the classical planets in Hellenistic astronomy, which were in turn named after contemporary deities, a system introduced by the Sume ...
, with Sundays excluded or included for everyone.


Effectiveness

The efficacy of odd–even rationing is debated. For gasoline, it does not actually reduce consumption much, since people prevented from filling up one day will just fill up the day before or the day after; the total number of people in line on each day is roughly unchanged. Some propose that it has psychological effects like reducing
panic buying Panic buying (alternatively hyphenated as panic-buying; also known as panic purchasing) occurs when consumers buy unusually large amounts of a product in anticipation of, or after, a disaster or perceived disaster, or in anticipation of a large p ...
, discouraging people from making small purchases on a daily basis, or emphasizing the shortage and further discouraging unnecessary trips. Rationing access, rather than gasoline, based on number plate parity can reduce
traffic congestion Traffic congestion is a condition in transport that is characterized by slower speeds, longer trip times, and increased vehicular queueing. Traffic congestion on urban road networks has increased substantially since the 1950s, resulting in m ...
. In some areas, wealthier people purposely own two cars with opposite-parity number plates, to circumvent any restrictions. Vanity plates which do not contain any digits may be arbitrarily classed as odd or even, likely using the last plate letter's numerical equivalent from 1 to 26.


Dealing with 0

Mathematically, zero is an even number; half of the numbers in a given range end in 0, 2, 4, 6, 8 and the other half in 1, 3, 5, 7, 9, so it makes sense to include 0 with the other even digits for rationing. However, the general public is not always aware of the mathematical principle and think that zero is odd, or both even and odd, or neither. The relevant law sometimes stipulates that zero is even. In fact, an odd–even restriction on driving in
Paris Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, largest city of France. With an estimated population of 2,048,472 residents in January 2025 in an area of more than , Paris is the List of ci ...
in 1977 did lead to confusion when the rules were unclear. On an odd-only day, the police avoided fining drivers whose plates ended in 0, because they did not know whether 0 was even.


U.S. gasoline rationing

Odd–even rationing was instituted in the U.S. as part of the response to the second gasoline crisis in 1979, when turbulent conditions in Iraq and Iran led to worldwide oil price increases, even though a supply shortage did not materialize in the U.S. After
Hurricane Sandy Hurricane Sandy (unofficially referred to as Superstorm Sandy) was an extremely large and devastating tropical cyclone which ravaged the Caribbean and the coastal Mid-Atlantic (United States), Mid-Atlantic region of the United States in late ...
hit the eastern coast in late October 2012, gasoline became scarce and caused lines to extend miles past stations and people to wait for hours to fill cars or gasoline tanks for generators powering houses without electricity. Panic buying and fuel hoarding began within days of the storm. On November 3, 2012, New Jersey governor
Chris Christie Christopher James Christie (born September 6, 1962) is an American politician and former United States Attorney, federal prosecutor who served as the 55th governor of New Jersey from 2010 to 2018. A member of the Republican Party (United States) ...
issued a gas rationing system to follow the odd–even rule to ease lines in 12 counties. A few days later on November 8, New York City Mayor
Michael Bloomberg Michael Rubens Bloomberg (born February 14, 1942) is an American businessman and politician. He is the majority owner and co-founder of Bloomberg L.P., and was its CEO from 1981 to 2001 and again from 2014 to 2023. He served as the 108th mayo ...
, along with Nassau County Executive Ed Mangano and Suffolk County Executive Steve Bellone, instituted an odd–even rationing system due to gasoline shortages from Hurricane Sandy. In New York City, such rationing lasted through November 23 due to the increased travel and gasoline demand during the
Thanksgiving Thanksgiving is a national holiday celebrated on various dates in October and November in the United States, Canada, Saint Lucia, Liberia, and unofficially in countries like Brazil and Germany. It is also observed in the Australian territory ...
week, while it ended more than a week earlier in the other counties. License plates without numbers, such as vanity plates, were considered odd.


India

In
Delhi Delhi, officially the National Capital Territory (NCT) of Delhi, is a city and a union territory of India containing New Delhi, the capital of India. Straddling the Yamuna river, but spread chiefly to the west, or beyond its Bank (geography ...
, during the ministry of
Arvind Kejriwal Arvind Kejriwal (; born 16 August 1968) is an Indian politician, activist and former bureaucrat, who served as the 7th Chief Minister of Delhi. He was the chief minister from 2013 to 2014 and from 2015 to 2024. He is also the national conve ...
, private
vehicle A vehicle () is a machine designed for self-propulsion, usually to transport people, cargo, or both. The term "vehicle" typically refers to land vehicles such as human-powered land vehicle, human-powered vehicles (e.g. bicycles, tricycles, velo ...
s could be on the road only on certain days, depending on their
license plate A vehicle registration plate, also known as a number plate (British, Indian and Australian English), license plate (American English) or licence plate (Canadian English), is a metal or plastic plate attached to a motor vehicle or trailer for ...
number, from January 1, 2016. The scheme aimed to reduce
pollution Pollution is the introduction of contaminants into the natural environment that cause harm. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the component ...
and
smog Smog, or smoke fog, is a type of intense air pollution. The word "smog" was coined in the early 20th century, and is a portmanteau of the words ''smoke'' and ''fog'' to refer to smoky fog due to its opacity, and odour. The word was then inte ...
in Delhi. The scheme was ended on November 11, 2017. The scheme came into force for the third time on November 4, 2019, after the success of first two times. The results were visible from the very first day as people of Delhi welcomed the move.


Indonesia

On August 30, 2016, the
Jakarta Jakarta (; , Betawi language, Betawi: ''Jakartè''), officially the Special Capital Region of Jakarta (; ''DKI Jakarta'') and formerly known as Batavia, Dutch East Indies, Batavia until 1949, is the capital and largest city of Indonesia and ...
city government replaced the "3-in-1" system (
high-occupancy vehicle lane A high-occupancy vehicle lane (also known as an HOV lane, carpool lane, diamond lane, 2+ lane, and transit lane or T2 or T3 lanes) is a restricted traffic lane reserved for the exclusive use of vehicles with a driver and at least one passenger, ...
s), which have attracted car jockeys trying to beat the system, with a system called ''ganjil-genap'' (odd/even rule). Odd plate numbers can enter former "3-in-1" areas on odd days and even plate numbers on even ones.


See also

* Road space rationing


References

{{DEFAULTSORT:Odd-even rationing Rationing Parity (mathematics) Vehicle registration plates