To prevent an accident such that a small projection formed on a work such as a guard rail installed along a traffic space such as a road comes into contact with an automobile during the traveling and a part of a vehicle body is removed and caught by the guard rail and prevent a secondary accident such that a person touches the caught iron piece.

In a complete method, the projection such as a bolt is buried in a body to be flush with each other. In this method, however, problems may occur in design, cost, and construction. Therefore, the projection is formed at the dead angle of motion of the automobile to prevent the accident from being enlarged. Specifically, a recessed part is formed and a dead angle is formed therein or a projected part is formed and a dead angle is formed on the side thereof.