Idaho Code § 49-1316
As a means of promoting safety upon the highways of this state, the transportation department, the state police and other law enforcement officers shall permit relatives or friends of a person killed in a traffic accident upon a highway of the state, with the consent of the next of kin of the deceased, to erect a traffic accident memorial in memory of the decedent. The traffic accident memorial shall be erected adjacent to the portion of the highway where the accident occurred so that the traffic accident memorial serves as a reminder that a fatality occurred on that stretch of highway and that public safety will thereby be enhanced. The transportation department shall promulgate rules to implement the provisions of this section, to provide size limitations the traffic accident memorial must conform to and to retain jurisdiction over areas where traffic accident memorials are placed.
Idaho Code § 49-1316