Individuals have to remember that many if not most of these type of locations are fresh energy spots or locations that the reason of death is not very long ago.
So the energy of the departed soul and the accident more than likely still lingers and is fresh.
Plus one has also to remember that the emotional energy of those that set up the memorials dedicated to the loved one they lost may keep the spirit of the loved on visiting there.
Remeber to respect the Spirit World, they do cross over, and no one is more powerful than the Spirit World, as it would not be allowed. No one can demand Spirits to do anything they are not willing to do in the first place.