Accident markers

On the east you never see lasting markers along the road of fatal car crashes, I've seen these before in my travels, and I simply don't get it, sure I understand that was the site of the loss of a loved one, the part I don't understand, is it seems to only be done when it's a motor vehicle accident....loved ones die in many places in many ways, but the spot isn't identified and remember for years...so to say the least I'm fascinated, and because I'm walking, I have the opportunity to view them up close, so expect to see many photos.  But only if they happen to be on my side of the street, not safe cris-crossing the main roads just for a picture