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24 CHAPTER 3 DATA COLLECTION AND PREPARATION This chapter describes the process followed to identify and implement the conventional marker type on a wide scale; select potential states to participate in the PRPM safety eval- however, no recent PRPM installations took place, and uation study. Two sections compose this chapter. First, the a suitable sample for a before-and-after safety evalua- process to select the states with potential data for this study is tion was not available. described. Second, details of the data collection activities fol- · To seek PRPM installations that took place during lows the state selection process. The research team devised 1995 or more recently. This decision leads to more procedures throughout the study to gather as much data as recent data files and provides the opportunity to analyze feasible, to test the quality of the data collected, and to pre- more current installations and markers and to develop pare the data sets to undergo the statistical analyses. guidelines based on the current PRPM practices and technologies. · To seek PRPM installations and related data at the 3.1 STATE SURVEY AND SELECTION following roadway types: two-lane undivided road- OF POTENTIAL STATES ways, four-lane divided expressways (at-grade inter- FOR PRPM SAFETY EVALUATION section control), and four-lane freeways (controlled access). The iTRANS survey indicated that PRPMs are To obtain a comprehensive knowledge of the state of the used extensively on four-lane divided roadways (express- practice relating to PRPMs and to assist the research team in ways and freeways) and two-lane undivided roadways. selecting candidate states for inclusion in the study, iTRANS Although PRPMs are also installed on four-lane undi- surveyed 29 states with known PRPM installations (see Table vided roadways and multilane freeways (i.e., with more 3-1). Information was obtained from these states through a than four lanes), the research team did not identify a suf- combination of questionnaires and telephone interviews. The ficient sample of these roadway types that met the other responses received from the states varied in their complete- criteria for this study. ness. Each response was assessed as a potential candidate for · To select states where it seems feasible to obtain inclusion in the proposed comprehensive evaluation plan. large samples of sites representing selective and non- After reviewing the material received by the research team selective PRPM implementation policies. An impor- and additional personal contacts, iTRANS selected the fol- tant issue that requires consideration during analysis is lowing states for the next stage of information assembling: the potential driver expectation and driver response to California, Illinois, Indiana, Maryland, Massachusetts, Michi- PRPMs when the PRPMs are implemented either selec- gan, Missouri, New Jersey, New York, Ohio, Oregon, Penn- tively at sites with known safety concerns or nonselec- sylvania, Texas, Utah, Virginia, and Wisconsin. The states tively using a systemwide approach. It is important to were requested to provide more detailed information on PRPM ensure that, in particular for two-lane treatment sites, installation locations, historical crashes, roadway inventory, there are representative samples of sites that are based and traffic volume databases. on both PRPM implementation policies. The research team made key decisions during the selection · To consider the states that have electronic crash data process: for at least 2 years before PRPM implementation and 1 year after PRPM implementation, as well as acces- · To confine the study to locations where raised snow- sible roadway inventory and traffic volume count plowable pavement markers have been installed. The information, preferably in electronic format. For the majority of current installations reported by the states safety evaluation, it is critical that data be available and were of the raised snowplowable marker type. States accessible in a useful format. that implement recessed markers either could identify only very small samples of roadways with this marker type or have discontinued their implementation in recent In conclusion, the following selection criteria were devised years. California and Texas were the only two states that when reviewing the information received from the states: