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28 for which crash data were collected, the data source, and the desirable for each of the roadway types. Table 3-10 lists the roadway referencing systems. Table 3-8 defines the crash roadway data files and their sources. The research team types used in the safety analysis. reviewed the data files to determine any missing data vari- Extensive examination of the data was undertaken. The iter- ables in the recorded databases or hard copies. For every ative process enabled the research team to improve and over- missing data variable deemed critical for comprehensive come most of the issues found in the databases. Some of these safety evaluation of PRPM installations, means to collect issues are described here. For example, during 1996, the loca- the information were explored, and whenever at all feasi- tion referencing system in Illinois changed. Before 1996, the ble, those variables were collected by the members of the reference for a route would restart at mile point zero each time research team. Some examples are described next. it crossed a county boundary. After 1996, the reference for a The data received for two-lane treatment and reference route would continue through the county boundary without group sites in New York and New Jersey contained no infor- restarting at mile point zero. This change in the referencing mation on horizontal alignment (e.g., curve location, curve system was reflected in the crash data files. To compute cor- radius, and curve length). This information for horizontal rect and comparable before-and-after crash totals for the dif- curves for New York and New Jersey was obtained from ferent PRPM roadway sections, the mile point data in the post- individual roadway design drawings, from New York DOT's 1996 crash and roadway attribute files for each PRPM route headquarters in Albany, and from New Jersey DOT's head- were aligned with the data of the pre-1996 referencing system. quarters in Trenton. Another example of data preparation is the assessment of Information on terrain type for New Jersey was obtained crash counts on freeways and expressways in Wisconsin. This from video-log recordings. Information on terrain type for data set revealed that there was a disproportionately greater Illinois was collected during field visits to District 8. number of crashes recorded involving vehicles traveling north Tables 3-11, 3-12, and 3-13 provide a summary of the road- and east than involving vehicles traveling south and west. way data collected at two-lane treatment sites for lane widths, This observed anomaly is likely the result of crashes being degree of curvature, and terrain type, respectively. Tables 3-14 miscoded. Therefore, the safety analyses for freeways and through 3-19 provide a summary of the roadway data collected expressways in Wisconsin considered the different travel for lane widths, shoulder widths, and environment types at ways together. four-lane freeway and four-lane expressway treatment sites. Non-intersection-related crashes were extracted from the databases for the safety analysis of PRPM installations along road segments. The daytime and nighttime crashes were 3.2.5 Traffic Volume Data defined on the basis of the sunset and sunrise times received from a national source of such times for different months of The variables required at treatment sites, reference group the year for each state (38). sites, and comparison group sites were AADT volumes, 3.2.4 Roadway Attribute Data Percentage of annual average nighttime traffic volumes, and Table 3-9 lists the roadway variables at PRPM and refer- Percentage of heavy vehicles. ence group sites according to their importance for the evalu- ation analysis. The variables were classified as critical or (text continued p. 31) TABLE 3-8 Crash type definitions Crash Type Definition Total All crashes reported and entered in the database Fatal and injury Crashes that resulted in fatal or nonfatal injuries Daytime Crashes that occurred between sunrise and sunset Nighttime Crashes that occurred between sunset and sunrise Dry Crashes that occurred on "road surface condition" reported as "dry" Wet Crashes that occurred on "road surface condition" reported as snow, wet, ice, or any other nondry conditions Wet-nighttime Crashes that occurred "road surface condition" reported as snow, wet, ice, or any other nondry conditions between sunset and sunrise Guidance-related Crashes with reported "impact type" as run-off-road, head-on, and sideswipe for fatal, injury, and property-damage-only combined Head-on Crashes with reported "impact type" as head-on for fatal, injury, and property-damage-only combined

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29 TABLE 3-9 Critical and desirable roadway variables Variables Two- Four-lane Four-lane lane expressway freeway Type of location (e.g., curve or tangent) Terrain type (flat, rolling, mountainous) Type of access control Roadway width Number of lanes Lane width Median type (e.g., raised, painted, and no median) NR Left and right shoulder types (e.g., surfaced and gravel) Horizontal alignment (e.g., degree of curve) Vertical alignment (e.g., grade and vertical curvature) Median width NR Left and right shoulder widths Design speed Speed limit 85th percentile speed = Critical variables. = Desirable variables. NR = Variables not relevant (two-lane roadways do not have medians). TABLE 3-10 Roadway data files and their sources State Data Files Received Source Illinois Sufficiency files for 1991, 1992, 1994, and Highway Safety 1997 to 2000 Information System (HSIS) Missouri Roadway inventory Missouri DOT Rumble strip inventory Median inventory New Jersey Straight line diagrams (1994 to 2001) New Jersey DOT New York Sufficiency files for 1991 to 2001 New York DOT Pennsylvania Roadway inventory Pennsylvania DOT Guiderail inventory Shoulder inventory Alignment data Wisconsin Highway log Wisconsin DOT TABLE 3-11 Summary information: lane widths at two-lane treatment sites State % of total % of total % of total % of total Minimum Maximum Average roadway roadway roadway roadway lane lane width lane length for length for lane length for lane length for width (ft) (ft) width lane widths widths lane (ft) widths > 10 ft and > 11 ft and widths 10 ft 12 ft >12 ft 11 ft Illinois 5.0 30.2 54.3 10.6 8.0 22.0 11.6 New Jersey 44.0 6.5 46.6 2.8 10.0 25.0 11.2 New York 2.4 22.8 72.2 2.6 10.0 25.0 11.8 Pennsylvania 13.7 32.3 45.6 8.4 8.0 32.0 11.8

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30 TABLE 3-12 Summary information: degree of curvature at two-lane treatment sites State % of total % of total % of total Minimum Maximum Average roadway roadway roadway DOC DOC DOC length length length when when when DOC = 0 DOC DOC > 3.5 3.5 Illinois 97.4 0.8 1.8 0.0 114.9 0.13 New Jersey 87.1 9.0 3.9 0.0 9.99 0.36 New York 68.5 18.7 12.8 0.0 76.4 4.04 Pennsylvania 50.0 35.6 14.4 0.0 68.24 1.61 DOC = degree of curvature. TABLE 3-13 Summary information: terrain type at two-lane treatment sites State % of total % of total % of total roadway roadway roadway length on flat length on length on terrain rolling terrain mountainous terrain Illinois 81.9 9.1 0.0 New Jersey 61.1 38.9 0.0 New York 61.5 38.5 0.0 Pennsylvania 85.0 15.0 0.0 TABLE 3-14 Summary information: lane widths at four-lane freeway treatment sites State % of total % of total % of total Minimum lane Maximum Average roadway roadway roadway width (ft) lane width lane width length length length (ft) (ft) when lane when lane when lane width width width 12 ft Missouri 0.1 98.7 1.2 11.0 18.0 12.0 New York 0.5 98.7 0.8 9.0 17.0 12.0 Pennsylvania 1.9 94.2 3.5 10.0 25.5 12.2 Wisconsin 0.0 99.7 0.3 12.0 18.0 12.0 TABLE 3-15 Summary information: shoulder widths at four-lane freeway treatment sites State % of % of total % of total % of total % of Minimum Maximum Average total roadway roadway roadway total shoulder width shoulder width shoulder width roadway length when length when length when roadway (ft) (ft) (ft) length shoulder shoulder shoulder length when width width width when shoulder > 4 ft and > 6 ft and > 8 ft and shoulder width 6 ft 8 ft 10 ft width 4 ft > 10 ft Missouri 8.2 2.9 2.2 86.7 0.0 3.0 10.0 9.3 New York 0.2 0.1 2.0 56.8 40.9 0.0 12.0 10.8 Pennsylvania 45.7 3.0 6.3 43.1 2.0 0.0 12.0 6.3 Wisconsin 0.3 0.4 63.1 33.7 2.5 0.0 13.0 8.5