01089690

Component

Typical types of retroreflective sheeting for use in most traffic signs include enclosed and encapsulated glass bead products, micro truncated cube corner prismatic products and, most recently, micro full cube corner prismatic products. These different sheeting types exhibit correspondingly different levels of sheeting performance. Historically sheeting retroreflectivity has been measured at specific photometric angle combinations, most notably 0.2 degree observation and -4 degree entrance angles. However, such measurements generally fail to correlate with on the road performance experienced by drivers in real nighttime driving scenarios. This paper discusses driver-focused design of the latest generation of retroreflective sheeting products. Of critical importance are the fractional retroreflectance or total amount of light returned to the vehicle and the distribution of that light with respect to observation angle (divergence). Fractional retroreflectance of typical retroreflective sheeting types is summarized and contrasted, as are the technologies used to increase total light return. Micro full cube corner sheeting is shown to provide the highest total light return, especially for the moderate entrance angles common in driving scenarios. Controlling the divergence of the retroreflected light (e.g. the distribution of that light with respect to observation angle) equates to controlling the appearance of signs as a function of vehicle-to-sign distance. Hence consideration of divergence during product design is critical for meeting driver needs. The importance of increased light return especially in the range of 0.5 to 1.0 degree observation angles is highlighted. Observation angles in this range correspond to the critical distances at which actual acquisition of information from signs occurs for a range of vehicle types. These critical distances are about 50 to 150 meters (164 to 492 feet). A variety of methods for controlling divergence are reviewed. Micro full cube corner sheeting is shown to provide significantly greater fractional retroreflectance and to concentrate the extra light return at critical sign distances.

01084478

08-1553

English

17p

2008

Transportation Research Board 87th Annual Meeting

DVD

Figures (6) ; References; Tables (2)

Glass beads; Retroreflectivity; Safety; Sign sheeting; Traffic control devices; Traffic signs

Highways; Operations and Traffic Management; Safety and Human Factors

Transportation Research Board Annual Meeting 2008 Paper #08-1553

TRIS, TRB

Jan 29 2008 3:53PM