65448035__WNBR____Wiki_information_site__4
[0] Circumstances blocking route (eg major road accident ahead, building fire) [1] very low [2] Police instructions [3] Cannot be foreseen depending on circumstances [4] 
In the event of a diversion, front marshal (who will have local knowledge of the area) will take the diversion, riders follow, police are likely to direct in these circumstances
Cardiff - World Naked Bike Ride (WNBR) - Wiki information site
4