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25 TABLE 3-1 States surveyed for establishing availability 3.2 DATA COLLECTION of data related to PRPM installations Arkansas Kentucky North Dakota This section provides an overview of the data collection California Maine Ohio and data preparation processes applied during the research project. To conduct a statistically defensible safety evalua- Colorado Maryland Oregon tion of PRPMs in a manner that will provide sufficient infor- Connecticut Massachusetts Pennsylvania mation to develop implementation guidelines, the following Florida Michigan Texas types of data were required: Georgia Minnesota Utah Illinois Missouri Virginia · PRPM treatment sites inventory, Indiana New Jersey West Virginia · Reference group and comparison group locations, Iowa New York Wisconsin · Historical crash data for all locations, Kansas North Carolina · Roadway attribute data for all locations, · Traffic volume data for all locations, and · Additional delineation and guidance measures at treat- ment locations. · The type of marker included raised snowplowable (retro- reflective) markers. The reference and comparison group location data were · Roadway types included two-lane undivided, four-lane required for developing safety performance functions to con- divided expressway (at-grade intersection control), and trol for changes in safety at treatment locations that are due four-lane freeways (controlled access). to factors other than PRPM installation (e.g., changes in traf- · Implementation dates were preferably between 1995 fic volume). and 1999. · Crash data included electronic crash data for at least 2 years before implementation and 1 year after imple- mentation. 3.2.1 PRPM Treatment Sites Inventory · Other data included accessible roadway inventory and traffic volume count information, preferably in electronic Electronic or hard-copy sources of the following variables format. relating to the installations of PRPMs were assembled for each state: On the basis of the information received, six states were selected for the safety evaluation of PRPMs: Illinois (Dis- · Beginning and ending route numbers and mileposts, trict 8), New Jersey, New York, Missouri, Pennsylvania (Dis- · Date or year of PRPM installation, tricts 1, 3, 5, and 8), and Wisconsin. Table 3-2 summarizes · Spacing (e.g., 40 ft or 80 ft), and the PRPM use in these six states. · Placement (e.g., centerline, edgeline, or lane lines). TABLE 3-2 States selected for the PRPM safety evaluation State Roadway Types PRPM Implementation Dates Policy Illinois Two-lane 1994 1999 Nonselective (District 8) New Jersey Two-lane 1993 Nonselective New York Two-lane 1998 Selective Four-lane freeway 1998 Nonselective Missouri Four-lane freeway 19922000 Nonselective Pennsylvania Two-lane 19922000 Selective (Districts 1, 3, 5, and 8) Four-lane freeway 19922000 Nonselective Four-lane 19922000 Nonselective expressway Wisconsin Four-lane freeway 1999 Nonselective Four-lane 1999 Nonselective expressway