01081147

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.

01081138

English

16p

2007-4

18th Biennial TRB Visibility Symposium

CD-ROM

Figures (6) ; References (3) ; Tables (2)

Design; Drivers; Functional analysis; Glass beads; Highways; Light; Performance; Retroreflection; Retroreflectivity; Sign sheeting; Traffic signs

Encapsulated sheeting; Microprismatic materials; Nighttime driving

Design; Highways; Planning and Forecasting; Safety and Human Factors; I21: Planning of Transport Infrastructure

TRIS, TRB, ATRI

Nov 23 2007 10:32AM

• A Review of Disability and Discomfort Glare Research and Future Direction
• Analysis of Modeled Versus On-the-Road Field Luminance of Retroreflective Signs
• Challenges to Implementation of Work Zone Lighting Guidelines
• Comparing Data Collection Scenarios Used for Examining Drivers' Sign Viewing Behavior: Closed Course Versus Open Road Environments
• Development of the Human Factors Guidelines (HFG) for Road Systems
• Driver Understanding of the Purpose of Red Retroreflective Raised Pavement Markings
• Effect of Outdoor Lighting on Perception and Appreciation of End-Users
• Evaluation of Road-Sign Geometry Parameter Space
• Fluorescent Orange Retroreflective Raised Pavement Marker Color Recognition Study
• I-95 Corridor Mile Marker and Ramp Designation Signing
• Modern Pavement Marking Systems: The Relationship Between Optics and Nighttime Visibility
• Pavement Marking Visibility: Brighter Versus Wider
• Performance Assessment of Vehicle Headlamps
• Recommendations for Minimum Pavement Marking Retroreflectivity Values Based on Tarvip Analyses
• Revealing Power and Road Lighting Design
• The Relationship of Vertical Illuminance to Pedestrian Visibility in Crosswalk