SPR Research Study No . C-0703 FINAL REPORT HIGH VISIBILITY REFLECTIVE SIGN SHEETING EVALUATION (original) (raw)
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Transport
Highway signs provide important information to drivers to assist in navigation, to identify potentially hazardous roadway locations, and to remind drivers of safe operating practices. Ensuring that signs have sufficient visibility to the driving public is a key undertaking by transportation agencies. In order to assist in evaluating and comparing different materials for photometric and visual performance, the present study was undertaken to assess the utility of specifying sign sheeting performance in terms of visual performance. As part of this effort, a practical methodology for conducting field measurements of sign luminance along roadways was developed. In addition to describing the methods for an approach to visual performance based specifications, a spreadsheet tool for calculating minimum sign luminance and visibility from different sign sheeting materials was also developed.
Title: Nighttime Photometric Evaluation of Unlighted Overhead Guide Signs
Overhead guide signs fabricated from four different retroreflective sheeting material combinations were photometrically (luminance and luminance contrast ratio) evaluated under low beam illumination at selected approach distances from 100 ft (30.5 m) to 1000 ft (305 m) using a 1984 Peterbilt Truck, a 2002 Chrysler Town and Country Minivan and a 2002 Toyota Camry, both with illumination by external luminaires ("lighted") and without illumination ("unlighted"). The photometric measurements were made with a ProMetric CCD Light and Color Measurement System. The luminance and luminance contrast ratio results indicate that under low beam illumination the Type VII legend on beaded Type III background sheeting material combination provides superior luminances and luminance contrast ratios for approach distances of 400 feet (122 m) or more while the Type IX legend on beaded Type III background sheeting material combination provides superior luminances and luminance contrast ratios for approach distances of less than 400 ft (122 m). For the three vehicles used, the legend luminances for the signs illuminated with luminaires and the automobile low beams are considerably higher, but have usually lower luminance contrast ratios when compared to the unlighted signs (for Type VII and Type IX legends on beaded Type III backgrounds). For instance, at 600 ft (183 m) the legend luminances for Type VII and Type IX legends on beaded Type III backgrounds range from 17 cd/m 2 to 57cd/m 2 when the signs are lighted and range from 4cd/m 2 to11cd/m 2 when the signs are unlighted and the luminance contrast ratios range from 4.2 to 9.4 when the signs are lighted and range from 4.3 to12.2 when the signs are unlighted which indicates that the legend luminances of lighted signs are 4-5 times higher, but have about up to 30% lower luminance contrast ratios when compared to the unlighted signs. Based on the results of the photometric evaluation and a separate expert panel field evaluation we conclude that unlighted overhead signs with either white Type VII or Type IX legends on green beaded Type III backgrounds provide adequate appearance, conspicuity, and legibility without sign luminaires.
Traffic Operational Impacts of Higher-Conspicuity Sign Materials
2003
Researchers examined the impacts of various higher-conspicuity sign materials on traffic operations and driver behavior. A total of eight applications of microprismatic materials were evaluated: fluorescent yellow Chevrons, fluorescent yellow Chevron posts, fluorescent yellow Curve signs, fluorescent yellow Ramp Speed signs, fluorescent yellow Stop Ahead signs, fluorescent red Stop signs, flashing red light emitting diodes Stop signs, and a red border on Speed Limit signs. Researchers installed these signs at locations where it was believed that improving sign conspicuity would provide a statistically significant benefit to safety-related traffic operations. Traffic operations data collected before and after the sign upgrades included vehicle speeds, edge line encroachments, and stopping compliance. Overall, the higherconspicuity applications produced mostly small changes in traffic operations, although many statistically significant beneficial results occurred. It should be pointed out that no negative driver behavioral impacts were found to be associated with any of the higher-conspicuity sign materials. Based on the findings, the researchers made recommendations pertaining to the application of higher-conspicuity sign materials. Fluorescent yellow Chevrons are recommended for statewide implementation. The other fluorescent yellow signs evaluated in the project are recommended for implementation on an as-needed basis. Microprismatic Stop signs are also recommended for implementation on an as-needed basis. Implementation of the flashing LED Stop sign and red border Speed Limit sign should be limited to an experimental basis, as permission is currently required from FHWA to install these signs. The fluorescent red Stop sign is not commercially available at this time.
Determining Cost-Effective Policy for Visibility of Overhead Guide Signs on Highways
Journal of the Transportation Research Forum
Overhead guide sign visibility on highway, can be achieved either by illumination or by using retroreflective sheeting. Two surveys were sent to all U.S. departments of transportation, to determine the states’ policies for increasing overhead guide sign visibility. Results showed that 57% of states currently illuminate guide signs, and the most used retroreflective sheeting by states that do not illuminate signs is Diamond Grade for legend and High Intensity for background. Based on cost analysis, the LED light source and the High Intensity (types III and IV) retroreflective sheeting are the most cost-effective methods for increasing guide signs visibility.
Recommended Guidelines for Nighttime Overhead Sign Visibility
Transportation Research Record: Journal of the Transportation Research Board, 2017
Guidelines for the provision of effective nighttime performance of overhead signs were developed. Relevant policies and guidelines with regard to sign lighting currently provide little useful information to determine when sign lighting is needed, and the reference material available to practitioners is out of date. Two complementary nighttime visibility studies were conducted, which were designed to produce results useful in developing updated guidelines for overhead sign visibility. The first was conducted on a closed course and investigated the legibility distances of three sign legend and background configurations under various sign lighting treatments. The second was conducted on the open road. It investigated the effects of sign luminance and visual complexity on the distance at which a driver can read overhead signs during a recognition task. The combined findings were used to develop revised guidelines designed to provide adequate nighttime visibility of overhead signs. The p...
Traffic Sign Sight Distance for Low-Volume Roads
Transportation Research Record, 2011
This study evaluated the field performance of asphalt pavements with and without slurry seal applications, developed performance models for asphalt pavements without slurry seals and asphalt pavements receiving slurry seals at various times following construction, and identified the optimum time for applying slurry seals on asphalt pavements in the Washoe County, Nevada, region. This determination was achieved by evaluating the long-term pavement performance data collected with the MicroPAVER system for the past 15 years and the cost-effectiveness of slurry seals applied to new and existing flexible pavements at Years 0, 1, 3, 5, 7, and 9 after construction. This study found that applying slurry seal immediately after or 1 year after construction of the asphalt layer is not effective in regard to the benefit to users and the benefit-cost ratio for the agency. The optimum time of applying slurry seal depended on the type of construction activity. For newly constructed pavements, the optimum time to apply slurry seal was 3 years after construction. For pavements subjected to overlays, the optimum time to apply slurry seal was between 3 and 5 years after construction. However, for uniformity purposes, it was recommended that the agency apply slurry seal 3 years after construction of the asphalt layer for both new and overlay constructions.
Field Evaluation of Unlighted Overhead Guide Signs Using Older Drivers
2003
Twenty older drivers, aged 63 to 81 (average 72.1), with corrected visual acuity ranging from 20/20 to 20/29 (average 20/25), evaluated six sign material and lighting combinations under nighttime conditions on US Route 30 near Mansfield, Ohio. The tested material combinations, all unlighted unless noted otherwise, were (legend on background) beaded Type III on beaded Type III, lighted beaded Type III on beaded Type III, Type VIII on microprismatic Type III, Type IX on beaded Type III, Type IX on Type IX, and Type VII on beaded Type III. Evaluators sat in the passenger seat and middle center seat of a 2002 Dodge Caravan. Headlights were kept on low beam. The evaluation loop was driven twice, once approaching signs in the left lane, and once approaching in the right lane. The evaluators completed questionnaires regarding sign visibility, legibility, and appearance after driving under each sign group and also an exit interview on the same topics at the end of the evaluation. Based on q...
Journal of the Society for Information Display, 2017
This study investigated drivers' visual perception of information displayed in LED traffic signs under different levels of environmental luminance. Concerning the information displayed, the environmental luminance comprised four luminance contrasts, two arrow types, and three environmental luminances, which were used to identify the visibility of traffic signs at the reading distance. Regarding visible distance, visibility involved reading starting and end points, extent of glare, comfortable distance, and glare distance. According to the study results obtained by using a highly reliable glare assessment method and studying the LED traffic signs, the lower the luminance contrast of traffic signs was the higher glare the participants perceived. A luminance contrast of 6200:2066 cd/m 2 provided the farthest comfortable and glare distances, enabling drivers to notice the signs comparatively earlier and have sufficient time to react accordingly. Overall, arrow type "<<<" outperformed "←" because the former was easier for drivers to read and created less glare. Regarding environmental luminance, traffic signs displayed in high and medium luminance environments (i.e., extremely sunny and cloudy days, respectively) each featured their own advantage, whereas those displayed in low luminance environments (nights) have to be further improved.