Good and Baxter indicated that further studies with larger sample sizes should be conducted to confirm their results.( 18) It is also imperative that the study include a sample of older drivers to ensure that the benefits of larger, more clear delineation to the older population is not discounted. Guidelines should include specific information as to when and where left edgelines should be supplemented by RPMs, perhaps using lighting and ADT criteria.ĥ. According to Pennell, RPMs should not supplement right edgelines unless: (a) there is a fixed obstruction (e.g., guardrail, trees, poles, bridge rails, ditches) or there are difficult traveling surfaces exceptionally close to the edge of the roadway, or (b) there is a lane drop or road width reduction.( 19)Ĥ. Although they found mixed results in research concerning overall accident reduction, a significant reduction in fatal and injury–producing accidents was found.( 3) The MUTCD currently states that a normal width of a longitudinal line should be 101.6–mm (4–in) to 152–mm (6–in) wide (1986).( 1) Pennell (1993) recommended that painted stripes (including edgelines) be applied with a 101.6–mm (4–in) width.( 19) It has been noted by the Roadway Delineation Practices Handbook (1994), however, that edgelines as wide as 203.2 mm (8 in) be considered to provide the elderly driver with better preview distances.( 2) However, this possibility was investigated by Hall (1987), who found no significant improvement in run–off–the–road accident occurrence as a result, it was recommended that the use of these 203.2–mm (8–in) edgelines be discontinued.( 20) Good and Baxter also investigated the use of wide edgelines and found that a width of 150 mm (5.9 in) was in fact beneficial to the driver a combination of wide edgelines and Post–Mounted Delineators (PMDs) (or RPMs)–for short–range and long–range information, respectively–would be ideal.( 18) Both lane line boundaries should therefore be delineated with RPMs supplementing the center line. found that edgelines on roadways greater than 6.1–m (20–ft) wide are recommended by several sources when they conducted a literature review. Justification: Blaauw (1985) states that, although a centerline provides lateral vehicle control inside the lane, it does not provide sufficient preview information–edgelining is therefore required.( 17) Good and Baxter (1986) found that continuous treatments were favored over discrete, and that wide edgelines were most beneficial to driver observation–control processes.( 18) Freedman et al. Right edgelines should not normally be supplemented by RPMs, unless stated for specific road conditions or geometry.Įdgelining should not be applied to roads narrower than 5.5 m (18 ft). Left edgelines should be supplemented by RPMs. RPM Reflectivity GENERAL DELINEATION REQUIREMENTSīefore discussing how RPMs should be used to delineate roadways, it is necessary to establish in general the type of delineation that is required by motorists.īoth center and edgelines are required to provide optimum driving performance.Ĭenterlines should be supplemented with RPMs as recommended per road geometry.Įdgelines should consist of a 152.4-mm (6-in) wide continuous stripe. The following section will present a collection of recommended practices along with future research issues, which can be used to complete an official set of guidelines for RPM use. Guidelines for the Use of Raised Pavement Markers
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