Object markers are used to mark obstacles within or next to the roadway and reduce the risk of collisions. They ensure road safety in the following ways:
Chevron Signs (MUTCD W1-8) indicate a change in the horizontal alignment of the roadway. Even narrowing of the road can be indicated with Chevron signs. You may find several of these signs on the outside of a sharp curve or approaches to a narrow bridge. On curves, chevron signs may be used as an alternate or supplement to standard delineators and edge lines. Both Chevron Alignment Left Sign and Chevron Alignment Right Sign are vertical rectangles with no border.
Delineators are used as guidance devices to help road users identify the alignment of the roadway. Rather than warning devices, delineators are considered guidance devices useful at night and in harsh weather conditions. Delineators should be installed in a series. Because of these reasons, MUTCD Section 3D.03 specifies that delineators shall match the color of the adjacent edge line.
On the other hand, object markers are used to mark obstructions within or adjacent to the roadway. Type 1 and Type 3 object markers are used to mark obstructions within the roadway and Type 2 and Type 3 object markers are used to mark obstructions adjacent to the roadway.
Obstructions on the road are required to be highlighted with object markers. Obstructions can be of various types like -
Type 1 object marker is either a marker consisting of nine yellow retroreflectors, each with a minimum diameter of 3 inches, mounted symmetrically on a yellow (OM1-1) or black (OM1-2) 18-inch diamond; or on an all-yellow 18-inch retroreflective diamond (OM1-3).
Type 2 object marker is either a marker (OM2-1V or OM2-1H) consisting of three yellow retroreflectors, each with a minimum diameter of 3 inches arranged either horizontally or vertically on a white panel measuring at least 6-inch x 12 inches or on an all-yellow horizontal or vertical retroreflective panel (OM2-2V or OM2-2H), measuring 6-inch x 12 inches.
Type 3 object marker is either a striped marker measuring 12 x 36 inches, consisting of a vertical rectangle with alternating black and retroreflective yellow stripes sloping downward at an angle of 45 degrees toward the side of the obstruction on which traffic is to pass. The minimum width of the yellow and black stripes shall be 3 inches. OM-3L object marker has diagonal stripes oriented from the top left to lower right. OM-3R object marker has diagonal stripes oriented from the top right to lower left. OM-3C object markers have diagonal stripes oriented from the center to the left and right.
End-of-Roadway Markers also called the Type 4 Object Markers, have their own category in the MUTCD. This type of sign may be designed in a button copy style with nine 3 ¼ inch red reflective buttons on a diamond shape aluminum panel. The panel shall have a red reflective or black non-reflective background (OM4-3). The most popular End-of-Roadway marker is a plain red retroreflective 18-inch diamond panel.
According to MUTCD Chapter 3C—Type 1, 2, and 3 Object Markers must be installed at least 4 feet above the ground measured from the bottom of the sign. There may be situations when the obstruction may require the sign to be mounted higher or lower too. Like, when used for marking objects in the roadway or objects that are 8 feet or less from the shoulder or curb, the mounting height should be at least 4 feet “above the surface of the nearest traffic lane.” End-of-Roadway markers too have at least a 4 feet minimum space requirement from the bottom of the diamond-shaped object marker to the edge of the pavement.