Some states take a hands-off approach to the memorial tradition, which is said to have American roots in the Southwest.
For more than a century, Hispanic mourners have marked the place where a funeral procession stopped to rest, according to a 1996 study by the New Mexico Oral History Project. The practice was simply reconfigured for the auto age.
"As an unwritten policy, we do not remove them," said New Mexico Department of Transportation spokesman S.U. Mahesh. "It is a sensitive issue here."
Rhetoric professor Van Hillard at Duke University in Durham, N.C., has studied commemorative practices such as roadside memorials. He said their origins are in Europe with roadside religious shrines.
More recently, they caught on after Princess Diana's death and tragedies at the World Trade Center and Oklahoma City bombing, he said.
"There's a tendency in our culture to try to ensure that people are remembered; that we don't forget," Hillard said. "There is a kind of trend to ensure memory, to retain memory; and I think they are working in that kind of vein."
The problem, Hillard said, is it seems to serve a purpose for a limited number of people, mainly the friends and families of the person who was killed.
"But for those who don't know the specifics of the accident, they also are rather mysterious," he said. "You go by and wonder, 'What happened here?' And in that way, they are unlike other public monuments and memorials that have the function of identification."
The federal government allows state transportation departments to determine rules regarding roadside memorials, according to the National Conference of State Legislatures. Thus, while most states have some policy regarding memorials, they vary greatly.
North Carolina is among more than a dozen states that ban the memorials, Hillard said.
Under threat of lawsuit by civil libertarians -- who say the crosses violate the constitutional division of church and state -- some states created bans. MnDOT officials said they haven't received any such threats.
Many states will provide standardized memorials or encourage family members to participate in Adopt-A-Highway programs. Some also have roadside memorial tree- and shrub-planting programs. North Carolina and Ontario name bridges after fallen police officers.
Texas, California and Montana only allow roadside memorials if alcohol was a factor in the crash. However, the families often must cover the cost of a permanent sign that includes an anti-drinking-and-driving message.
Wisconsin, New Jersey and some other states let families put up memorials for a limited time but not on freeways or interstates.
"We do essentially allow them for about a year," said John Kinar of the Wisconsin Department of Transportation.
Wisconsin transportation officials established guidelines called "Memorials on the Highway: Remembering a Loved One" after a 50-vehicle pileup that killed 10 in Sheboygan County in 2003.
Like New Mexico, many states only remove the memorials if they clearly present a safety hazard.
West Virginia allows grieving families to place temporary and permanent memorials. The 3-year-old system titled "We Respect Your Feelings" requires notification of the State Highway Department or obtaining a permit for a permanent marker.
"This is not West Virginia, thank gosh," Bray said. "Minnesota is a bit more ahead of the game. West Virginia can do as they wish. But for us, it is a safety issue pure and simple."
