Sadly they are not illegal in Montana, and on top of that, the state puts a cross by the road everywhere a fatal accident took place, and leaves it there for, I think, about 7 years. Though, if I remember right, some civic minded group actually takes care of them, not the government. I'm not sure about that part.
And there are roads where there is a cross every mile, and this in a state where the annual traffic death total is under 150 a year (but our per 100,000 rate is twice the national average)
The public ones are bad enough. The private ones are indeed a nuisance. And many last for much more than 7 years. There is a roadside cross south of where I live about 15 miles that a)has been there since I moved here in 1989 and b) has a little white picket fence and a two foot, nicely mown lawn. Others are constantly re-adorned with beads and ribbons and christmas wreaths, etc. on a regular basis. Both the private and state ones.
And Nam is absolutely right. We don't mark or cherish the place of death where others kicked the bucket. We don't cherish the places where people got murdered or dropped dead of a heart attack at the mall. There is no rhyme nor reason.
Oh, and not all traffic victims die at the scene. Many die on the way to the hospital, or in the hospital. So accuracy is not too important either.
As human flaws go, though, I wish this was the worst one. It isn't even close.
Psychologists have recognized that in the realm of time, there are three basic types of people. Those that live in the present, those that live in the future, and those that live in the past. Among those that live in the past are those that are caught up in genealogy. And presumably, in putting crosses by the road. Those that live in the future can save for retirement like a boss but don't seem to do anything about their needs today. And those of us who live in the present give no thought to all the time we're wasting not the Internet when we could be accomplishing something useful that would help us in the long run. So we've all got our quirks.
I just don't mark mine with a cross or a teddy bear. There aren't enough in the world.