Traffic delineators are known. Delineators are typically used on or near roadways or other paved or unpaved surfaces where automobiles, trucks, or other motorized or unmotorized vehicles travel. Often a series of delineators are arranged along a road, lane, or path so as to highlight or increase its visibility for the benefit of vehicle operators. FIG. 1 is an idealized perspective view of a roadway 110 along which delineators 112 have been placed to mark the path or direction of the roadway. Delineators can also be used in construction work zones to help guide vehicles along rerouted paths that may be unfamiliar to the vehicle operators. Perhaps because delineators can be used to direct or “channel” traffic in a given direction, they are sometimes also referred to as channelizers.
In some cases, delineators may be used in applications where visibility from only one direction is considered important. In other cases, e.g., when placed between lanes of traffic that move in opposite directions, it may be important for the delineator to exhibit high visibility from both such directions. In still other cases, such as at intersections, it may be important for the delineator to exhibit high visibility from four or more different directions, e.g., north, south, east, and west.
An example of a known delineator design is simply a post attached to a base. For improved visibility, the post may comprise high visibility materials. For daytime visibility, the post may be fabricated from bright diffuse materials, such as white or orange paint. For nighttime visibility, retroreflective sheeting may be wrapped around a portion of the post. Retroreflective sheeting has the characteristic of directing incident light back in the general direction from which it came, regardless of the angle at which the light impinges on the surface of the sheeting. Thus, as a vehicle approaches a roadway sign or other structure on which a retroreflective sheet is mounted, light from a vehicle headlamp may impinge on the sheeting, which then reflects the light back in the general direction of the headlamp. The retroreflection occurs in a small but finite angular cone, which cone encompasses the eye of the vehicle operator so that the operator perceives the sign as being conspicuously bright and highly visible.
FIGS. 2 and 3 are provided for background purposes to exemplify two angles that may have some significance when discussing retroreflective sheeting, or other reflective sheeting. FIG. 2 is a top view of a vehicle 210 traveling in a direction 212 along a roadway 214. Reflective sheeting 216 is provided near the side of the road. Sheeting 216 is assumed to be flat and planar, and the axis 218 is perpendicular to the plane of the sheeting. (In cases where the reflective sheeting is not flat, each portion of the sheeting may be considered to be flat if the size of the portion is small enough.) Axis 220 represents the direction along which light from the vehicle headlamp impinges upon the sheeting 216. The angle β between the axes 218 and 220 is referred to as the entrance angle for the light. A side view of this situation is shown in FIG. 3, where the vehicle headlamp (or other light source) is shown separately and labeled as 310, and the eye of the vehicle operator (or other observer) is shown separately and labeled 312. An axis 314 extends directed between the headlamp 310 and the sheeting 216. Another axis 316 extends between the sheeting 216 and the observer 312. The angle α between the axes 314, 316 is referred to as the observation angle.