A temporary reference line inscribed across the crown of the left-hand rail
in exactly the same longitudinal position as the display. Used to assist
measurement during PositioningThe process of establishing the optimum Position of a proposed Signal or Element. or SightingThe process of evaluating the effectiveness of an installed Signal or Element by means of on-site observation of Visibility and Readability. a SignalA visual display device which conveys instructions or provides prior warning of instructions regarding the driver’s authority to proceed..