Selecting the Optimal Sheeting-Font Combination to Increase the Visibility of Roadway Guide Signs in the Presence of Glare

Abstract

OCCUPATIONAL APPLICATION Roadway guide signs provide directional and mileage information to specific destinations. These signs are produced by combining different types of retroreflective sheeting materials along with different font types. Some sheeting-font combinations increase nighttime visibility to drivers, while other combinations do not. We compared two types of sheeting materials along with two font types. A field experiment was conducted at night, in the presence of glare from an oncoming vehicle's low beam headlights. A cost comparison was also performed. The most cost-effective sheeting-font combination was type XI sheeting and ClearviewHwy™ font. These results may be useful for Departments of Transportation to increase legibility distance and the visibility of shoulder-mounted guide signs for drivers, and consequently help increase roadway safety. TECHNICAL ABSTRACT Background: Driver safety remains an important issue, and improving roadway guide sign visibility is an important step in increasing safety on roadways and thus reducing crashes. Currently, two types of retroreflective sheeting materials (type IV and type XI) and either Series E (Modified) or ClearviewHwy font types are used for signs in the United States. Glare from an oncoming vehicle's low beam headlights, however, can create visual difficulty for drivers at night. Purpose: The purpose of this study was to evaluate the performance of two retroreflective sheeting materials and two font types, for use on shoulder-mounted guide signs (i.e., mounted on the shoulder of a roadway) in the presence of glare. Methods: Four sheeting-font combinations, involving type IV and type XI sheeting materials and Series E (Modified) and ClearviewHwy fonts were compared in a field experiment. Participants were asked to read the legend of four signs during nighttime driving, in the presence of glare from an oncoming low beam headlight vehicle. The legibility distance at which the participant read the sign was recorded as the dependent variable. A cost comparison was also performed for the four signs. Results: Type XI sheeting combined with ClearviewHwy font provided the maximum legibility distance. The cost analysis showed that type XI was less expensive over a 60-year timeframe (∼9.3% lower) versus type IV. Conclusions: Use of type XI sheeting and ClearviewHwy font is recommended for shoulder-mounted roadway signs to enhance legibility. However, future work is needed to verify these results under more general conditions and with a broader range of participants.