Road space rationing, also known as alternate-day travel, driving restriction and no-drive days (; ; ), is a travel demand management strategy aimed to reduce the negative externalities generated by urban air pollution or peak urban travel demand in excess of available supply or road capacity, through artificially restricting demand (vehicle travel) by rationing the scarce common good road capacity, especially during the peak periods or during peak pollution events. This objective is achieved by restricting traffic access into an urban cordon area, city center (CBD), or district based upon the last digits of the license number on pre-established days and during certain periods, usually, the peak hours.
The practical implementation of this traffic restraint policy is common in Latin America, and in many cases, the road rationing has as a main goal the reduction of air pollution, such as the cases of México City, and Santiago, Chile. São Paulo, with a fleet of 6 million vehicles in 2007, is the largest metropolis in the world with such a travel restriction, implemented first in 1996 as measured to mitigate air pollution, and thereafter made permanent in 1997 to relieve traffic congestion. More recent implementations in Costa Rica and Honduras have had the objective of reducing oil consumption, due to the high impact this import has on the economy of small countries, and considering the steep increases in oil prices that began in 2003. Bogotá, Quito, and La Paz, Bolivia also have similar driving restriction schemes in place.
After a temporary implementation of road space rationing to reduce air pollution in Beijing during the 2008 Summer Olympics, local officials put in place several permanent rationing schemes to improve the city's air quality. , another 11 Chinese cities have similar restriction schemes in place. Also, temporary driving restrictions to reduce cars on the streets by half during severe pollution events have been implemented in Paris and surrounding suburbs in March 2014, March 2015, and December 2016; in Beijing twice in December 2015, and one more time in December 2016; and also in Rome and Milan for several days in December 2015. A similar alternate-day travel temporary scheme was implemented in New Delhi as a two-week trial in January 2016. A temporary ban on diesel cars was implemented in Oslo on municipal roads in January 2017.
Historical background
The earliest known implementation of road space rationing took place in Ancient Rome, as carriages and carts pulled by horses created serious congestion problems in several Roman cities. In 45 B.C. Julius Caesar declared the center of Rome off-limits between 6 a.m. and 4 p.m. to all vehicles except for carriages transporting priests, officials, visitors, and high-ranking citizens.
Effectiveness
Schemes rationing access based on number plate have mixed results. If used infrequently or temporarily the alternate-day travel policy can have some impact. However, if used as a long term measure, inequality issues might arise, as wealthier people can afford to own two cars with opposite-parity number plates, to circumvent any restrictions, with the second vehicle being often older and therefore more polluting. Cities such as Tehran which have used such schemes are now looking to more sustainable methods of traffic and emissions control, such as low emission zone or traffic limited zones as used in Europe. Access regulations have often been found to be effective, in reducing congestion, traffic and pollution.
The program's impact on moving behavior to more sustainable transport methods is also unclear. Evaluations on the effectiveness of road space rationing regulations focus mainly on whether there is a decrease in the usage of the less sustainable vehicles for which the schemes were implemented in the first place. They do not focus on whether there is a change in the pattern in which such vehicles are used. For example, evaluations examine how many people stop using a polluting car. They do not evaluate how many people start riding bicycles or carpool as a result of such schemes.