{HEAD ~ A database} that represents the road network is used to determine {TAIL ~ locations} where an intersection of roads is located at the bottom of a hill and then, precautionary action data is added to the database to indicate such locations 
{ HEAD ~ A database } that represents the road network is used to determine { TAIL ~ locations } where an intersection of roads is located at the bottom of a hill and then , precautionary action data is added to the database to indicate such locations
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL REL REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH