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44 CHAPTER 6 GUIDELINES FOR THE USE OF SNOWPLOWABLE PRPMS This chapter describes some of the current warrants and or not there are warrants for pavement markings when con- guidelines for pavement markings and markers as background sidering the definition above. for the development of guidelines for the use of PRPMs. It For PRPMs, there are no statements in the MUTCD as to then proposes guidelines for the use of snowplowable PRPMs the conditions that would warrant their use. A PRPM is rec- based on the research study findings documented in Chap- ognized as a "device that is intended to be used as a posi- ter 5. The analytical engineering procedures included in the tioning guide or to supplement or substitute for pavement proposed guidelines are illustrated for two-lane roadways. markings." Standard, Guidance, and Option statements relate how to use PRPMs once it is decided to use them. (It could be argued that since PRPMs may be used as a "substitute for 6.1 BACKGROUND pavement markings" [Section 3B.14], then if an agency pre- fers to use PRPMs over painted pavement markings, there is The "Manual on Uniform Traffic Control Devices" (Sec- a requirement [Standard] for when PRPMs are to be used for tion 1A.13) (3) defines a warrant for a traffic control device centerline markings [Section 3B.01].) as follows: The 2001 edition of the Traffic Control Devices Hand- book (47) recognizes PRPMs as providing excellent visibility A warrant describes threshold conditions to the engineer in at night and in the rain. PRPMs are discussed from a materials evaluating the potential safety and operational benefits of standpoint, and no guidance is provided as to when PRPMs traffic control devices and is based upon average or normal should be used. conditions. Warrants are not a substitute for engineering judg- ment. The fact that a warrant for a particular traffic control The "Roadway Delineation Practices Handbook" (2) devotes devices is met is not conclusive justification for the installa- an entire chapter to PRPMs. The advantages of PRPMs are tion of the device. noted. Principal disadvantages are a high initial cost and the need for more expensive snowplowable markers in snowfall The MUTCD contains a limited number of warrants. There areas. Because of the high cost of PRPMs, the "Handbook" are warrants for notes that their use is limited to important roadways where additional delineation is needed and to roadways having a sur- · Traffic signal installation (Section 4C.01), face that will not soon be subjected to major repair, replace- · Centerline markings and left edgeline pavement mark- ment, or excavation. Little information is provided on how to ings (Section 3B.01), determine what is an important roadway or where additional · No-passing zone pavement markings (Section 3B.02), delineation is needed. Narrow bridges on two-lane rural · White lane line and right edgeline pavement markings roads are mentioned as a special type of location where (Section 3B.04), and PRPMs were found to be effective in reducing nighttime · Edgelines (Section 3B.07). speeds and centerline encroachments. A project performed by the University of Iowa for the For traffic signalization, there are eight specific warrants, FHWA resulted in "Guidelines for the Use of Raised Pave- each of which provides conditions to be met to justify a traf- ment Markers" (5). These guidelines suggest that PRPMs fic signal. The MUTCD emphasizes, however, that the satis- should be installed faction of a traffic signal warrant or warrants shall not in itself require the installation of a traffic signal. In compari- · To supplement double yellow centerlines on two-lane son, the warrants for the pavement markings noted above are curves; less clear and are embedded or inferred within statements · To delineate centerlines and edgelines where there are under the Standard, Guidance, and Option sections. For exam- pavement width reductions at a narrow bridge; ple, there are conditions where a centerline marking is required · At painted gores, exits, and bifurcations; (Standard), where they are recommended (Guidance), and · On all freeways and Interstate highways (snowplowable where they are permitted (Option). It could be argued whether PRPMs); and