Roadside markers are common here in Oregon, too, especially along Hwys 18 and 22–they get a lot of tourist traffic to the casinos and the coast.
I read a Readers’ Digest article a few years ago about the 20 most dangerous highways in America. I can’t remember the location, but a community action group took the liberty of putting up crosses for every death along one stetch of highway. In a mile stretch, they had several dozen. And for a month there were no accidents. But the DOT insisted the crosses were a hazard that would distract drivers, so they took them all down. Very next day, there was a fatality accident.
One more note: about 10 years ago, my family drove across Montana and I seem to recall seeing dozens of iron crosses along the roads, especially on curvy stretches. My dad said the state put them up; instead of imposing speed limits, they try to use scare or guilt tactics to make drivers be careful. I don’t know whether or not it works.