No stopping or loading is allowed on the 109-mile network from 6am until 12pm to every day.
The route includes 30 miles of Games Lanes reserved for members of the 'Olympic family' – athletes, sponsors and officials. Transport for London (TfL) said the lanes would operate flexibly and could be open to all traffic if demand from Olympic vehicles is low.
More than 1,300 traffic signals have been adjusted, along with other changes like road markings, temporary traffic islands and barriers. Once Olympic events are completed at a venue, the ORN will be removed from that area.
In April, Mark Evers, director of Games transport for TfL, said at Event's Guide Live that 70% of London's road network will be unaffected by the Games.
Up to one million visitors are expected in London every day during the Olympics, adding an extra three million journeys to the usual 12 million daily trips made on public transport.
TfL is advising drivers to avoid central London and to check transport hotspots at getaheadofthegames.com before travelling.
Meanwhile, the first Olympic sporting event kicks off this afternoon at the Millenium Stadium in Cardiff, where Team GB's women football team will take on New Zealand at 4pm.
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