Short Answer:
Animal crossing, Children's play, Sharp turn ahead, Railway crossing.
Long Answer:
Speed limits could be posted where it is common for animals to cross the decrease the number of roadkill around. It is also possible that there will be a decreased speed limit where children are playing nearby so the driver doesn't accidentally hit them. Sharp turns are also a hazard because motorcycle riders could think no other drivers are on the road and speed up, then get hit by a car. Railway crossings also induce a decreased speed limit. So all those are possible options.
Hope this helps.
