The total number of riders in a road race will be restricted to 176, with teams restricted to seven riders in men's one-day and shorter races, and eight for Grand Tours to improve safety in races.
The Management Committee of the Union Cycliste Internationale (UCI) approved the introduction of the new regulations governing team sizes at a meeting at the World Championships in Bergen, Norway, on Tuesday.
In a statement issued by the UCI, it says the regulations will apply to all events in the UCI International Road Calendar.
The Grand Tours comprise the Giro d'Italia, Tour de France and Vuelta a España. Prior to the new rule, teams consisted of nine riders in each race.
Women's WorldTour races will now include teams of six riders for one-day events and seven for stage races.
The UCI says the new regulations have been introduced to "improve the safety of the riders, spectators and the race convoy".
The reduction in the number of riders in races comes after calls have been made in recent seasons after a spate of incidents involving race vehicles colliding with riders.
Most notably, Belgian rider Antoine Demoitié of the Wanty-Groupe Gobert team died of his injuries after colliding with a race motorbike during the 2016 edition of Ghent-Wevelgem.
Regulations have already been introduced by the UCI to restrict the number of race vehicles, and how they move around within races.
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