Why not commemorate something more meaningful than how someone tragically died? I think they should put a memorial where the deceased loved someone, or something. Or maybe a tribute bench. Those are awesome. I always read the plaque about another gentleman or lady who sat by the sea, or loved to sail, or maybe was generous or a loving brother. Being reminded of some horrific accidental death daily is disconcerting.
Eventually, our highways will look like cemeteries. I don't think people should clutter roadsides with anything.
If they feel the need to have a roadside memorial, why not plant flowers or a tree (if it's far enough away from the road)? It would feel your need to grieve by remembering the place and instead of depressing other people, they'll see the beauty of life. And it's also better for the land and the environment.
My mum made the point, "If we're going to put crosses on the side of the road, why not put little markers EVERYWHERE someone's died, like in hospitals and stuff? Then if you go to the hospital, you can see who all died in your bed."