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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:
