Safety Evaluation of Permanent Raised Pavement Markers (2004) / Chapter Skim
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From page 4... ...
Standard paint lines are ineffective during rainy conditions because rain often accumulates on the painted markings, thus reducing the retroreflectivity of the paint, whereas the raised pavement markers stand above the pooled water (2)
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This finding confirms Endres's (9) conclusion that raised pavement markers out-perform recessed markers under dry and wet weather conditions.
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For example, Maryland implements PRPMs nonselectively on all Interstate highways and other freeways. Maryland, Massachusetts, and Wisconsin use the speed limit of a roadway as a primary criterion for deciding where to implement PRPMs.
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Daytime crashes included daytime, dawn, and dusk crashes, while nighttime crashes included crashes with and without street lighting present. Crash types potentially affected by PRPMs -- namely head-on, sideswipe, and run-off-road -- were identified for a separate analysis.
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From page 8... ...
The daytime crashes were again used as a comparison group to account for any factors that may have influenced crash frequency between the before and after periods but that were not related to the PRPM installation. However, daytime crashes did not include crashes occurring during dusk or dawn; dusk and dawn crashes that were eliminated from the analysis were reported to be about 1–3 percent of the total crashes.
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From page 9... ...
The overall, or average, effect of PRPM installation on nighttime crashes was estimated by calculating a weighted log odds ratio. The log odds ratio, L, is calculated by taking the natural logarithm of T, defined previously in Equation 2-1.
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From page 10... ...
The first analysis, at 20 sites, targeted PRPMs at sections of unlit suburban and rural roadways with proportionately high numbers of nighttime and nighttime wet weather crashes. Overall, there was a nonsignificant decrease of 7 percent for total crashes, a highly significant decrease of 26 percent for nighttime crashes, and a significant decrease of 33 percent for nighttime wet weather crashes.
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From page 11... ...
Pennsylvania Interstate highways in rural nonilluminated areas Does not specify I – 1992-1995 B – 1-3 years A – 1-3 years Treatment – 3376 locations depending on crash type studied Comparison – same as treatment group Total nighttime crashes, nighttime wet road, nighttime wet road sideswipe fixed-object None Total daytime crashes, daytime wet road, daytime wet road sideswipe or fixed-object Both raised and recessed reflective markers were used 18.1% overall increase in nighttime crashes, nighttime wet condition crashes increased from 30 to 47%, nighttime wet road sideswipe or fixed-object increased by 56.2% New York
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From page 12... ...
of the second study, with its troubling result, continued to show a statistically significant increase in nighttime crashes at some locations. As will be seen in Section 2.3, there are mixed findings with respect to speed and an indication that speed effects may be site specific.
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From page 13... ...
in their analysis of the Pennsylvania data. As indicated earlier, the authors suspected that PRPMs may have had a positive effect on the daytime crashes used for the comparison group that generated the result that PRPMs caused only a marginal decrease in nighttime crashes.
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. Visibility distances were determined through measurements of the optical characteristics of the PRPMs, combined with data from experiments with subjects.
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Figure 2-2 shows visibility distances 22 months after application on a highway lane with an AADT of 3,062 veh/day. As can be seen, visibility distances for in-service devices are reduced by as much as half of that of newly installed devices.
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Yellow Line None None 2 4-in. Yellow Line 4-in.
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From page 17... ...
. There were significant differences between left- and rightcurve recognition distances for some treatments and between older and younger drivers for other treatments.
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From page 18... ...
on curves up to 15 degrees • 20 ft (6 m) on curves with more than 15 degrees of curvature • No significant difference in mean speeds – nighttime 85th percentile speeds reduced significantly • Speeds increased on one approach and decreased on the other • Smoother speed profile (only night results)
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From page 19... ...
with the use of raised pavement markers; daytime mean vehicle speeds increased by a similar amount. In a nighttime study comparing the impact of PRPMs supplementing the existing centerline with post-mounted delineators, Krammes and Tyer (34)
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The study recommended that PRPMs be introduced slightly in advance of the highway problem area to prepare motorists for the guidance technique that is to be encountered. 2.3.3.4 Driver Speed and Lane Position in Relation to PRPM Spacing on Tangents and Ramps Optimal spacings for PRPMs along tangent sections and on interchange ramps of Interstate highways in Ohio were determined by Zwahlen (29)
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From page 21... ...
Statistical analysis showed no significant difference in speed or lane positioning related to the presence or spacing of PRPMs on ramp sections; thus, the placement of PRPMs on the outer edgelines of cloverleaf interchange ramps was not recommended. Zwahlen's study (29)
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From page 22... ...
Significant reduction in nighttime 85th percentile speeds -- no significant difference in daytime speeds 2. Vehicle speed at night increased (no mention of daytime speeds)
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From page 23... ...
. 23 With respect to speed, findings were very mixed, with two studies finding smoother speed profiles through curves (29, 30 night only at one sight)
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