Saving the "Acceident alert" history can be used to generate "This crossing had many acceidents - be carefull" icon. It can be just a "yellow/orange/red/purple" dot or /!\ sign on the map near the road.
I recomand that no more then 10 such icons will be shown on the map at the same time, and only along the path used.

It is based on existing data, and no editing is needed.