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OCR for page 58
HFG MARKINGS Version 1.0 POST-MOUNTED DELINEATORS Introduction Post-mounted delineators (PMDs) are a type of marking device used to guide vehicles along a roadway. The AASHTO Green Book (1) specifies that delineators shall be retroreflective devices mounted above the roadway surface and along the side of the roadway in a series to indicate the alignment of the roadway. Delineators are particularly useful at locations where the alignment might be confusing or unexpected, such as at lane reduction transitions and/or curves (2). They are also useful at night and during adverse weather. Delineators may be used on long sections of highways or on short sections where there are changes in horizontal alignment. An important advantage of delineators is that they remain visible when the roadway is wet or snow covered. Design Guidelines Spacing: Drivers respond similarly to fixed and variable spacing of delineators when perceiving curvature. Thus, either spacing method can be used for outlining the curve approach and departure segments. MUTCD (2) RECOMMENDATIONS FOR DELINEATOR SPACING ON CURVES Radius of Curve (ft) 50 115 180 250 300 400 500 600 700 800 900 1000 Approximate Spacing 20 25 35 40 50 55 65 70 75 80 85 90 (S) on Curve (ft) VARIABLE AND FIXED SPACING FOR CURVE APPROACHES AND DEPARTURES 2S 3S 6S VARIABLE SPACING S 2S 2S 2S FIXED SPACING (3 ) (2 ) S S S Preview Times Post-mounted delineators should be visible with a preview time of at least 5 s. Number of Reflectors There is no difference in curve perception between single and double delineators; thus, either is acceptable for curve delineation. Color Drivers are not aware of the varying meanings of differently colored delineators. If differently colored delineators are used, drivers should receive education as to their specific meanings. Based Primarily on Based Equally on Expert Judgment Based Primarily on Expert Judgment and Empirical Data Empirical Data 20-8

OCR for page 58
HFG MARKINGS Version 1.0 Discussion Spacing: Charlton (4) found that drivers' perceptions of speed and curvature appear to work at both a conscious (explicit) and unconscious (implicit) level. For this reason, curve warnings and delineation treatments that highlight the sharpness of the curve ahead or increase a drivers' momentary sense of their apparent speed appear to offer promise in allowing drivers to enter curves at a lower speed. Delineation treatments may also assist drivers with selecting and maintaining appropriate lane position while travelling throughout the curve. Chrysler, Carlson, and Williams (3) found that drivers cannot distinguish between fixed and variable delineator spacing on the approaches to horizontal curves. The two types of spacing led to functionally equivalent curve perceptions. Thus, Chrysler et al. (3) recommend that the approach and departure delineator spacings be fixed at two times the appropriate curve spacing found in the MUTCD. This recommendation can save installation time without sacrificing safety. More specific information on spacing on horizontal curves can be found in the MUTCD. Preview time: Rumar and Marsh (5) explained two complementary road guidance functions: short-range and long- range guidance. Long-range guidance (over 5 s of preview time) allows the driver to consciously predict the path of the roadway far in advance, drive smoothly, and avoid time-pressure situations. Rumar and Marsh (5) found that preview times provided by lane markings alone are well under a safety criterion of 5 s and thus concluded that current lane markings are not optimal for safe night driving. Good & Baxter (6) found the addition of PMDs tends to have a positive effect for long-range guidance, but have no effect on short-range guidance. To be usable for long- range guidance, PMDs should be visible at a preview time of at least 5 s (about 440 ft at 60 mi/h (140 m at 100 km/h)) under low-beam illumination. Number of reflectors: Chrysler et al. (3) found that the perception of curvature is not affected by the number of reflectors on the delineator. However, the combination of one reflector and variable spacing leading up to the curve caused the perception of less curvature. Overall, Chrysler et al. (3) recommend that the MUTCD eliminate the distinction between the two types of delineators and define a standard delineator. Larger delineators could still be used for emphasis where necessary. Color: Chrysler et al. (3) found that drivers do not understand the difference in placement for yellow and white delineators. Although response accuracy was poor for curve delineator color, when given a forced-choice question regarding crossover delineation, most drivers could recognize the correct color. This finding led to the recommendation of putting more emphasis on delineator color in driver education courses rather than altering the MUTCD. Design Issues Another use of delineators is to define the roadway leading up to a railroad grade crossing. At rural crossings without active warning devices, the lighting may be poor and drivers may be more reliant on auditory train signals to know if a train is approaching. However, these auditory signals may not be completely effective for drivers who are hearing impaired. Staplin, Lococo, Byington, and Harkey (7 ) found that approximately 30% to 35% of people aged 65 to 75 have a hearing loss, increasing to 40% for persons over the age of 75. The use of post-mounted delineators would help highlight to hearing-impaired drivers that railroad crossing is imminent. Cross References None. Key References 1. AASHTO (2004). A Policy on Geometric Design of Highways and Streets. Washington, DC. 2. FHWA (2009). Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD). Washington, DC. 3. Chrysler, S.T., Carlson, P.J., and Williams, A.A. (2005). Simplifying delineator applications for horizontal curves. Transportation Research Record, 1918, 68-75. 4. Charlton, S.G. (2007). The role of attention in horizontal curves: a comparison of advance warning, delineator, and road marking treatments. Accident Analysis & Prevention, 39(5), 873-885. 5. Rumar, K., and Marsh, D.K., II (1998). Lane Markings in Night Driving: A Review of Past Research and of the Present Situation. (UMTRI- 98-50). Ann Arbor: University of Michigan Transportation Research Institute. 6. Good, M.C., and Baxter, G.L. (1985). Evaluation of Short-Range Roadway Delineation (Internal Report No. AIR 381-1). Melbourne: Australian Research Board. 7. Staplin, L., Lococo, K., Byington, S., and Harkey, D. (May 2001). Guidelines and Recommendations to Accommodate Older Drivers and Pedestrians (FHWA-RD-01-051). McLean, VA: FHWA. 20-9