The alternate circulation relates to restrictions put on circulation, based on a prohibition for certain periods of time.

Roads

Work and demonstrations

A section of road in work, which allows the passage of the vehicles only on one way, is often put in alternate circulation . fires are placed at the two ends and manage the traffic. It is the case also when a sporting event or other prevents the normal access to the roads.

Collars, throats, bridges

Circulation on the mountain roads where the crossing is dangerous or impossible is sometimes limited on a time basis. Places presenting a great tourist interest and a too great number of vehicles can also know the alternate circulation , like the Gorges of Galamus (the every day in summer of 13:00 to 19:00).

Bidirectional ways

Highways, bridges or tunnels include/understand one or more lanes which are allotted in one or the other direction according to the importance of the traffic. See ( reversible lane ).

More the completely reversible long roads are with the Brésil, between São Paulo and sea (58.5 km). It counts 10 ways in 4 groups (3+3+2+2), each group being able to be reversed.

Trucks

In the alpine tunnels where the density of the vehicles is strictly controlled, the Camion S are sometimes authorized to circulate only in an alternate way . It was the case with the Road tunnel of Gothard in 2002: alternate circulation every two hours the morning and every four hours the afternoon. Following the catastrophe in the tunnel of Mont Blanc in 1999, the alternate circulation of the Truck S.A. also be until March 2003.

Mobility

Concept of exclusive right of way to alternate management .
Certain cities like Barcelona and Caluire (Lyon) practice restrictions of circulation which vary according to the hours of the day. The goal can be to facilitate in turn: parking of the residents the night, deliveries the morning, and the circulation of the cars or public transport in the course of the day. In Caluire, the buses circulate on the exclusive right of way in direction of the center town the morning, and the evening towards the periphery. Chambéry plans to make in the same way.
The idea is to equitably share the roadway system in the most convenient direction, according to the moments.

Pollution

Several big cities introduced into their payments the possibility of the alternate circulation . This provision, rather exceptional, can occur following strong pollution and in bad conditions of atmospheric dispersion, the purpose of it is to contribute to decrease or limit the harmful effects of pollution on health.

Concretely, the restriction applies to a given sector and for a given period. The motor vehicle traffic is prohibited day after day, in an alternated way, except for the or not polluting authorized vehicles, according to the final figure of the number plate. It is the system known as of the “even and odd numbers”.

; France Alternate circulation is a regulation, applicable by prefectoral decision pursuant to a Order of the prefect, at the time of a point of noted or imminent Pollution atmospheric, relating to the going beyond of the " threshold of alarm " order of the prefect in force.

; Greece The cloud of pollution which overhangs Athens is called the néfos . Alternate circulation was founded in a restricted perimeter and does not achieve its goals, being circumvented in various ways by the inhabitants.

; Italy Rome.

; Mexico Mexico City

; Switzerland The Council of State of the Canton of Geneva can introduce an exceptional regulation of the traffic (alternate circulation) when the concentration of PM10 (pollution due to the fine particles) exceeds 150 μg/m3 (micrograms per cubic meter). Geneva is currently the only Swiss canton to have such a legislation.

Rivers

A alternate circulation governs the crossing of Paris on the the Seine, the large arm between the bridge of Sully and the bridge with the Exchange. Each full hour allows the passage in each direction during 15 to 20 minutes.

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