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OCR for page 54
HFG MARKINGS Version 1.0 EFFECTIVENESS OF SYMBOLIC MARKINGS Introduction Effectiveness of symbolic markings refers to the degree to which drivers follow and understand text or symbols on the roadway. A major component of pavement markings is horizontal signing, which is composed of sign text that is painted on the roadway. Horizontal signing is effective because drivers spend most of their time scanning the roadway in front of their vehicle near the horizon (1). Because drivers are already looking at the pavement, they are likely to see information there more quickly, preventing the need for an eye movement away from the road. Additionally, the pavement can be a good location to provide lane-specific information. Design Guidelines Marking Do this: Do not do this: Goal Reduce speeds in horizontal curves Curve arrow and "Curve 55 mph" text Transverse lines "Curve Ahead" text "50 mph" text Reduce wrong-way movements N/A on two-way frontage roads Lane direction arrows on a two-way frontage road by an off-ramp Provide route guidance Route shield in the exiting lane Route name text in the exiting lane information for lane drops N/A Pavement marking arrows (in addition to traditional lane drop markings) Based Primarily on Based Equally on Expert Judgment Based Primarily on Expert Judgment and Empirical Data Empirical Data 20-4

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HFG MARKINGS Version 1.0 Discussion Speed reduction in horizontal curves: In an on-road study of horizontal signing to reduce speeds before horizontal curves, Chrysler and Schrock (1) found that the text "Curve 55 mph" reduced speeds on a rural road by approximately 4 mi/h more than the control treatment. Although this finding was not statistically significant, the benefit from this marking was greater than for the "Curve Ahead" text (which did not cause a significant reduction). When the curve arrow and "50 mph" text were tested on an urban roadway, vehicles significantly reduced their speeds by 10% at the entrance to the curve. There was also an 11% to 20% reduction in vehicles exceeding the speed limit. Note that the curve arrow and "50 mph" text were tested in a section of the road following a vertical crest, so the arrow provided additional information about the direction of the curve after drivers came over the crest. Another option if advisory speeds cannot be displayed is the text "SLOW" with a curve arrow. Retting and Farmer (2) tested this marking on a suburban road and found that it significantly reduced the percentage of drivers exceeding the speed limit by more than 5 mi/h during the daytime and late night time frames, but not during the evening. Overall, the markings that provided advisory speeds or an action performed most effectively. The results of transverse line treatments have been mixed. Chrysler and Schrock (1) found that a series of three pairs of transverse lines near the middle of the lane did not cause a significant speed reduction. However, Katz (3) found that transverse lines at the lane edges resulted in speed reductions, which were significant on interstate and arterial roadways, but not rural roadways. Note that the treatments differed in multiple ways. Chrysler and Schrock (1) attempted to create a "visual rumble strip," which would appear in the driver's foveal vision, on a rural road. Katz (3) used markings at the lane edges, which would appear in the driver's peripheral field of view and create the illusion of higher than actual speed. Wrong-way movements on two-way frontage roads: Chrysler and Schrock (1) tested the implementation of lane direction arrows on a frontage road in Texas. The use of one-way and two-way frontage roads is widespread in Texas, potentially increasing the probability of wrong-way movements. Lane direction arrows were placed on the frontage road, 120 ft from the gore area of the exit onto the road. With the arrows installed, the rates of wrong-way driving maneuvers and conflicts were significantly reduced by 90% and almost 100% respectively. This overwhelming reduction in wrong-way driving indicates that the treatment can have a beneficial safety influence on traffic at locations where drivers may be confused about appropriate lane selection. Lane drops: In a study of route guidance information regarding lane drops, Chrysler and Schrock (1) surveyed drivers about route markers. The majority (94%) of respondents preferred the route shield over the route name text. However, 29% to 48% of drivers thought that the marking indicated the route they were currently on rather than the upcoming exit. Therefore, route shields may be effective when used with other lane drop signs/markings. Fitzpatrick, Lance, and Lienau (4) tested another lane drop indicator: pavement marking arrows. With the addition of pavement marking arrows, erratic maneuvers such as lane changes through the gore and attempted lane changes decreased. Drivers continuing on the main route moved out of the exit lane earlier. Although these results were only significant for two out of the three sites tested, the other site had a lane drop only 1.6 km (1 mi) long, and vehicles may have shifted through the exit lane upstream of the study segment. Design Issues Horizontal signing has two issues that can be broadly applied: visibility of the markings and durability of the materials on the travel lane. Horizontal markings viewed during daytime must contrast with the road surface. White markings may not provide an adequate contrast for symbol recognition or word legibility when viewed against a concrete or worn asphalt surface. Conversely, nighttime visibility is affected by the durability of the optical elements presented in the marking material, typically glass beads. Other visibility limitations can be found in shortened headways due to traffic congestion that may not be large enough for full horizontal sign viewing. Horizontal signs should have large simple components and should be visually unique to the highest possible degree. Proper application using text or symbols should minimize the use of abbreviations, keeping the symbols simple and legible. By limiting the application to critical locations, drivers will be able to recognize these signs as an added warning or caution (5). Chrysler and Schrock (1) determined that when drivers are undergoing stressful driving conditions or situations where too much information is presented at one time, they will practice "load shedding" by ignoring the least important information and focus ing on the more important tasks. Drivers will tend to look at the road more and at side or overhead-mounted signing less when "load shedding" takes place. This behavior increases the importance of horizontal signing in the area where drivers look most. Cross References None. Key References 1. Chrysler, S., and Schrock, S. (2005). Field Evaluations and Driver Comprehension Studies of Horizontal Signing (FHWA/TX-05/0-4471-2). College Station: Texas Transportation Institute. 2. Retting, R.A., and Farmer, C.M. (1998). Use of pavement markings to reduce excessive traffic speeds on hazardous curves. ITE Journal, 68(9), 30-34, 36. Retrieved from: http://www.ite.org/membersonly/itejournal/pdf/JIA98A30.pdf. 3. Katz, B.J. (2004). Pavement Markings for Speed Reduction. McLean, VA: Turner-Fairbank Highway Research Center. Retrieved from: http://www.pooledfund.org/documents/TPF-5_065/speed_reduction.pdf. 4. Fitzpatrick, K., Lance, M., and Lienau, T. (1995). Effects of pave ment markings on driver behavior at freeway lane drop exits. Transportation Research Record, 1495, 17-27. 5. Chrysler, S., Schrock, S., and Williams, A. (2006). Research Recommendations for Pavement Marking Words and Symbol s. College Station: Texas Transportation Institute. 20-5