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Safety Evaluation of Permanent Raised Pavement Markers (2004)

Chapter: Chapter 3 - Data Collection and Preparation

« Previous: Chapter 2 - Review of PRPM-Related Literature and Jurisdictional Practices
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Suggested Citation:"Chapter 3 - Data Collection and Preparation." National Academies of Sciences, Engineering, and Medicine. 2004. Safety Evaluation of Permanent Raised Pavement Markers. Washington, DC: The National Academies Press. doi: 10.17226/13724.
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Suggested Citation:"Chapter 3 - Data Collection and Preparation." National Academies of Sciences, Engineering, and Medicine. 2004. Safety Evaluation of Permanent Raised Pavement Markers. Washington, DC: The National Academies Press. doi: 10.17226/13724.
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Suggested Citation:"Chapter 3 - Data Collection and Preparation." National Academies of Sciences, Engineering, and Medicine. 2004. Safety Evaluation of Permanent Raised Pavement Markers. Washington, DC: The National Academies Press. doi: 10.17226/13724.
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Suggested Citation:"Chapter 3 - Data Collection and Preparation." National Academies of Sciences, Engineering, and Medicine. 2004. Safety Evaluation of Permanent Raised Pavement Markers. Washington, DC: The National Academies Press. doi: 10.17226/13724.
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Suggested Citation:"Chapter 3 - Data Collection and Preparation." National Academies of Sciences, Engineering, and Medicine. 2004. Safety Evaluation of Permanent Raised Pavement Markers. Washington, DC: The National Academies Press. doi: 10.17226/13724.
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Suggested Citation:"Chapter 3 - Data Collection and Preparation." National Academies of Sciences, Engineering, and Medicine. 2004. Safety Evaluation of Permanent Raised Pavement Markers. Washington, DC: The National Academies Press. doi: 10.17226/13724.
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Suggested Citation:"Chapter 3 - Data Collection and Preparation." National Academies of Sciences, Engineering, and Medicine. 2004. Safety Evaluation of Permanent Raised Pavement Markers. Washington, DC: The National Academies Press. doi: 10.17226/13724.
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Suggested Citation:"Chapter 3 - Data Collection and Preparation." National Academies of Sciences, Engineering, and Medicine. 2004. Safety Evaluation of Permanent Raised Pavement Markers. Washington, DC: The National Academies Press. doi: 10.17226/13724.
×
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Suggested Citation:"Chapter 3 - Data Collection and Preparation." National Academies of Sciences, Engineering, and Medicine. 2004. Safety Evaluation of Permanent Raised Pavement Markers. Washington, DC: The National Academies Press. doi: 10.17226/13724.
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24 CHAPTER 3 DATA COLLECTION AND PREPARATION This chapter describes the process followed to identify and select potential states to participate in the PRPM safety eval- uation study. Two sections compose this chapter. First, the process to select the states with potential data for this study is described. Second, details of the data collection activities fol- lows the state selection process. The research team devised procedures throughout the study to gather as much data as feasible, to test the quality of the data collected, and to pre- pare the data sets to undergo the statistical analyses. 3.1 STATE SURVEY AND SELECTION OF POTENTIAL STATES FOR PRPM SAFETY EVALUATION To obtain a comprehensive knowledge of the state of the practice relating to PRPMs and to assist the research team in selecting candidate states for inclusion in the study, iTRANS surveyed 29 states with known PRPM installations (see Table 3-1). Information was obtained from these states through a combination of questionnaires and telephone interviews. The responses received from the states varied in their complete- ness. Each response was assessed as a potential candidate for inclusion in the proposed comprehensive evaluation plan. After reviewing the material received by the research team and additional personal contacts, iTRANS selected the fol- lowing states for the next stage of information assembling: California, Illinois, Indiana, Maryland, Massachusetts, Michi- gan, Missouri, New Jersey, New York, Ohio, Oregon, Penn- sylvania, Texas, Utah, Virginia, and Wisconsin. The states were requested to provide more detailed information on PRPM installation locations, historical crashes, roadway inventory, and traffic volume databases. The research team made key decisions during the selection process: • To confine the study to locations where raised snow- plowable pavement markers have been installed. The majority of current installations reported by the states were of the raised snowplowable marker type. States that implement recessed markers either could identify only very small samples of roadways with this marker type or have discontinued their implementation in recent years. California and Texas were the only two states that implement the conventional marker type on a wide scale; however, no recent PRPM installations took place, and a suitable sample for a before-and-after safety evalua- tion was not available. • To seek PRPM installations that took place during 1995 or more recently. This decision leads to more recent data files and provides the opportunity to analyze more current installations and markers and to develop guidelines based on the current PRPM practices and technologies. • To seek PRPM installations and related data at the following roadway types: two-lane undivided road- ways, four-lane divided expressways (at-grade inter- section control), and four-lane freeways (controlled access). The iTRANS survey indicated that PRPMs are used extensively on four-lane divided roadways (express- ways and freeways) and two-lane undivided roadways. Although PRPMs are also installed on four-lane undi- vided roadways and multilane freeways (i.e., with more than four lanes), the research team did not identify a suf- ficient sample of these roadway types that met the other criteria for this study. • To select states where it seems feasible to obtain large samples of sites representing selective and non- selective PRPM implementation policies. An impor- tant issue that requires consideration during analysis is the potential driver expectation and driver response to PRPMs when the PRPMs are implemented either selec- tively at sites with known safety concerns or nonselec- tively using a systemwide approach. It is important to ensure that, in particular for two-lane treatment sites, there are representative samples of sites that are based on both PRPM implementation policies. • To consider the states that have electronic crash data for at least 2 years before PRPM implementation and 1 year after PRPM implementation, as well as acces- sible roadway inventory and traffic volume count information, preferably in electronic format. For the safety evaluation, it is critical that data be available and accessible in a useful format. In conclusion, the following selection criteria were devised when reviewing the information received from the states:

25 • The type of marker included raised snowplowable (retro- reflective) markers. • Roadway types included two-lane undivided, four-lane divided expressway (at-grade intersection control), and four-lane freeways (controlled access). • Implementation dates were preferably between 1995 and 1999. • Crash data included electronic crash data for at least 2 years before implementation and 1 year after imple- mentation. • Other data included accessible roadway inventory and traffic volume count information, preferably in electronic format. On the basis of the information received, six states were selected for the safety evaluation of PRPMs: Illinois (Dis- trict 8), New Jersey, New York, Missouri, Pennsylvania (Dis- tricts 1, 3, 5, and 8), and Wisconsin. Table 3-2 summarizes the PRPM use in these six states. 3.2 DATA COLLECTION This section provides an overview of the data collection and data preparation processes applied during the research project. To conduct a statistically defensible safety evalua- tion of PRPMs in a manner that will provide sufficient infor- mation to develop implementation guidelines, the following types of data were required: • PRPM treatment sites inventory, • Reference group and comparison group locations, • Historical crash data for all locations, • Roadway attribute data for all locations, • Traffic volume data for all locations, and • Additional delineation and guidance measures at treat- ment locations. The reference and comparison group location data were required for developing safety performance functions to con- trol for changes in safety at treatment locations that are due to factors other than PRPM installation (e.g., changes in traf- fic volume). 3.2.1 PRPM Treatment Sites Inventory Electronic or hard-copy sources of the following variables relating to the installations of PRPMs were assembled for each state: • Beginning and ending route numbers and mileposts, • Date or year of PRPM installation, • Spacing (e.g., 40 ft or 80 ft), and • Placement (e.g., centerline, edgeline, or lane lines). TABLE 3-1 States surveyed for establishing availability of data related to PRPM installations Arkansas Kentucky North Dakota California Maine Ohio Colorado Maryland Oregon Connecticut Massachusetts Pennsylvania Florida Michigan Texas Georgia Minnesota Utah Illinois Missouri Virginia Indiana New Jersey West Virginia Iowa New York Wisconsin Kansas North Carolina State Roadway Types PRPM Implementation Dates Policy Illinois (District 8) Two-lane 1994 –1999 Nonselective New Jersey Two-lane 1993 Nonselective Two-lane 1998 Selective New York Four-lane freeway 1998 Nonselective Missouri Four-lane freeway 1992–2000 Nonselective Pennsylvania (Districts 1, 3, 5, and 8) Two-lane 1992–2000 Selective Four-lane freeway 1992–2000 Nonselective Four-lane expressway 1992–2000 Nonselective Wisconsin Four-lane freeway 1999 Nonselective Four-lane expressway 1999 Nonselective TABLE 3-2 States selected for the PRPM safety evaluation

26 It became evident that there are very few differences in the PRPM implementation practices among states. On two- lane roadways, the general practice is to implement two-way yellow PRPMs only on the centerline at a spacing of 80 ft (24 m). On most curves, the spacing of PRPMs is reduced to 40 ft (12 m). Table 3-3 shows the proportion of the total length of two- lane PRPM treatment sites where PRPMs were implemented at a spacing of either 40 ft (12 m) or 80 ft (24 m). On freeways and expressways, the general practice is to implement one- way, white PRPMs on the lane line only at a spacing of 80 ft. Table 3-4 provides a summary of the all treatment site data used in the analysis. 3.2.2 Reference and Comparison Group Sites For states in the study group that have selective implemen- tation policies (i.e., Pennsylvania and New York), samples of untreated roadways of the relevant roadway types were iden- tified to compose a reference group from which safety per- formance functions (SPFs) or crash prediction models were calibrated for each year of the analysis period. Table 3-5 sum- marizes the reference group data used for this study. In states where PRPMs were installed nonselectively (e.g., for four-lane freeways in Wisconsin, Missouri, and Penn- sylvania and for two-lane roadways in Illinois and New Jer- sey), the reference group information used for calibrating SPFs made up the before-period data collected for sites with State % that had 40-ft (12-m) PRPM spacing % that had 80-ft (24-m) PRPM spacing Illinois 0.5 99.5 New Jersey 1 unknown unknown New York 11.1 88.9 Pennsylvania 5.3 94.7 1 The spacing of PRPMs at treatment sites in New Jersey could not be confirmed from the videolog recordings received from New Jersey DOT. TABLE 3-3 Percentage of two-lane treatment sites with 40-ft and 80-ft PRPM spacings TABLE 3-4 Summary of treatment site data used in the analysis Before Period After Period Crash Count Crash Count State/ Road Type Miles (Sites) Mile- Years Average AADT (veh/ day) Total Fatal and Injury Mile- Years Average AADT (veh/ day) Total Fatal and Injury All two-lane roadways 983 5153 NA 8970 3011 2615 NA 6006 2166 Illinois two-lane roadways 460 2755 2850 2783 706 1139 2650 1133 292 New Jersey two-lane roadways 174 348 10944 1522 656 696 10951 2508 1219 New York two-lane roadways 82 409 9140 1431 1000 164 9650 1121 424 Pennsylvania two- lane roadways 267 1641 5486 3234 649 616 5887 1244 231 All four-lane freeways 2713 17201 NA 42472 11906 6330 NA 16058 4074 Missouri four-lane freeways 1441 10929 14007 25565 8271 3488 16844 9195 2720 New York four-lane freeways 37 185 15390 326 180 74 16370 335 91 Pennsylvania four- lane freeways 779 3807 24995 5750 741 2312 29920 3640 501 Wisconsin four-lane freeways 456 2280 20900 10831 2714 456 22970 2888 762 All four-lane expressways 251 1228 NA 2899 487 471 NA 1122 210 Pennsylvania four- lane expressways 106 503 13810 725 126 326 16200 531 86 Wisconsin four-lane expressways 145 725 11770 2174 361 145 12590 591 124

PRPMs. This meant that data availability for the purpose of calibrating the SPFs would be nonexistent for the period after nonselective installations were implemented and could be scarce toward the completion of the nonselective installa- tions statewide. To calibrate the SPFs for these later years, a comparison group of sites was identified that consisted of as- yet untreated locations or locations on which PRPMs had been installed prior to the beginning of the study period. The comparison group accounted for time trends throughout the SPF calibration period. Special attention was given by the research team when selecting roadways to avoid any road- ways near PRPM locations in order to minimize the influence of any spillover or migration effects. Because of the widespread implementation of PRPMs in Illinois, it was not possible to select a suitable comparison group of sites in this state. Thus, for this state, SPFs were fit- ted to the data for the later years of the after period to develop time trend factors for these later years. However, in Wisconsin, the widespread implementation of PRPMs on four-lane freeways and expressways during 1999 resulted in very limited comparison group data for a total of 43 miles of four-lane freeway. To address this constraint and to account for time trends in more recent years (i.e., 1998–2000), the research team collected additional data for urban Interstate highways in Madison County, Wisconsin. 3.2.3 Crash Data The crash databases obtained from each state contained the variables listed in Table 3-6. Table 3-7 shows the period 27 Road type State Description Miles Mile- years All crashes Fatal and injury crashes Average AADT Two-lane roadways Pennsylvania Untreated two-lane roadway sections 170 1690 2332 455 4517 New York Untreated two-lane roadway sections 182 1683 2400 1211 4300 New Jersey Before-period data of treatment sites 191 1337 8737 3338 12737 Illinois Before-period data of treatment sites 460 2755 2783 706 22850 Four-lane freeways Missouri Before-period data of treatment sites 1826 14801 30274 9642 13560 Pennsylvania Before-period data of treatment sites 779 3807 5750 741 24995 New York Untreated two-lane roadway sections 122 1098 3387 1497 12870 Wisconsin Before-period data of treatment sites 456 2280 10831 2714 20900 Four-lane divided expressways Pennsylvania Before-period data of treatment sites 106 503 725 126 13810 Wisconsin Before-period data of treatment sites 145 725 2174 361 11770 TABLE 3-5 Summary and description of reference site data used in the analysis Category Variable Time variables Crash date Crash time Environmental variables Road surface condition Weather condition Light condition Crash-related variables Impact type Crash severity Initial direction Vehicle maneuver Alignment Location type (intersection vs. nonintersection) Roadway variables Route number Milepost or reference point and offset TABLE 3-6 Crash data variables obtained from each state TABLE 3-7 Crash data period, source, and roadway referencing system State Period Source Referencing System Illinois 1991–2000 Highway Safety Information System (HSIS) County, route, milepoint Missouri 1991–2000 Missouri DOT Route, milepoint New Jersey 1991–1998 (excluding 1996) Internet/New Jersey DOT Route, milepoint New York 1991–2000 New York DOT Reference marker Pennsylvania 1991–2001 Pennsylvania DOT County, route, segment, offset Wisconsin 1994–2001 Wisconsin DOT Route, reference point, offset

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

29 Variables Two- lane Four-lane expressway Four-lane 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 3-9 Critical and desirable roadway variables State Data Files Received Source Illinois Sufficiency files for 1991, 1992, 1994, and 1997 to 2000 Highway Safety Information System (HSIS) Missouri Roadway inventory Rumble strip inventory Median inventory Missouri DOT 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 Guiderail inventory Shoulder inventory Alignment data Pennsylvania DOT Wisconsin Highway log Wisconsin DOT State % of total roadway length for lane widths ≤ 10 ft % of total roadway length for lane widths > 10 ft and ≤ 11 ft % of total roadway length for lane widths > 11 ft and ≤ 12 ft % of total roadway length for lane widths >12 ft Minimum lane width (ft) Maximum lane width (ft) Average lane width (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 TABLE 3-11 Summary information: lane widths at two-lane treatment sites TABLE 3-10 Roadway data files and their sources

30 TABLE 3-12 Summary information: degree of curvature at two-lane treatment sites State % of total roadway length when DOC = 0 % of total roadway length when DOC ≤ 3.5 % of total roadway length when DOC > 3.5 Minimum DOC Maximum DOC Average DOC 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 roadway length on flat terrain % of total roadway length on rolling terrain % of total roadway length on 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 roadway length when lane width < 12 ft % of total roadway length when lane width = 12 ft % of total roadway length when lane width > 12 ft Minimum lane width (ft) Maximum lane width (ft) Average lane width (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 total roadway length when shoulder width ≤ 4 ft % of total roadway length when shoulder width > 4 ft and ≤ 6 ft % of total roadway length when shoulder width > 6 ft and ≤ 8 ft % of total roadway length when shoulder width > 8 ft and ≤ 10 ft % of total roadway length when shoulder width > 10 ft Minimum shoulder width (ft) Maximum shoulder width (ft) Average shoulder width (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

31 Table 3-20 describes the AADT data received and data sources for each state. For Wisconsin, New Jersey, and Illi- nois, AADT data could not be obtained for each year of the study period. Estimation procedures, using the existing counts, were applied in the calculation of the missing AADT volumes. None of the data files received from the study group states contained information on the percentage of annual average nighttime traffic (i.e., annual average traffic between sunset and sunrise). Permanent traffic counting stations (which col- lect continuous annual traffic counts) and average monthly sunrise and sunset times were used to estimate the percent- age of annual average nighttime traffic at the various road- ways. 3.2.6 Additional Delineation and Guidance Measures Information was collected on the following additional delin- eation and guidance measures: • Illumination, • Rumble strips, and • Delineation (e.g., chevrons and post-mounted delineators). Since none of the data files received from the states con- tained information on these additional delineation and guid- ance measures, the research team followed other data collec- tion strategies (see Table 3-21). Tables 3-22, 3-23, and 3-24 show the percentage of two- lane treatment sites with and without illumination, additional delineation (e.g., chevrons and post-mounted delineators), and shoulder rumble strips, respectively. The states reported that chevrons are not placed on four- lane freeways and expressways. However, post-mounted delineators are placed along freeways at a spacing of 60 to 100 ft (18 to 30 m). Less than 1 percent of four-lane freeway and expressway sites are illuminated. Tables 3-25 and 3-26 show the percentage of treatment site length with and without shoulder rumble strips for free- ways and expressways, respectively. State % of total roadway length (urban) % of total roadway length (rural) Missouri 19.1 80.9 New York 32.1 67.9 Pennsylvania 29.7 70.3 Wisconsin 12.6 87.4 State % of total roadway length when lane width < 12 ft % of total roadway length when lane width = 12 ft % of total roadway length when lane width > 12 ft Minimum lane width (ft) Maximum lane width (ft) Average lane width (ft) Pennsylvania 11.0 78.9 10.1 8.0 25.0 12.4 Wisconsin 0.0 97.2 2.8 12.0 18.0 12.0 State % of total roadway length when shoulder width ≤ 4 ft % of total roadway length when shoulder width > 4 ft and ≤ 6 ft % of total roadway length when shoulder width > 6 ft and ≤ 8 ft % of total roadway length when shoulder width > 8 ft and ≤ 10 ft % of total roadway length when shoulder width > 10 ft Minimum shoulder width (ft) Maximum shoulder width (ft) Average shoulder width (ft) Pennsylvania 54.0 6.1 21.3 8.9 9.7 0.0 12.0 4.8 Wisconsin 0.4 1.6 73.2 19.8 5.0 2.0 13.0 8.5 TABLE 3-16 Summary information: environment type at four-lane freeway treatment sites TABLE 3-17 Summary information: lane widths at four-lane expressway treatment sites TABLE 3-18 Summary information: shoulder widths at four-lane expressway treatment sites

32 TABLE 3-21 Additional delineation and guidance measures: data collection strategies State Data Collection Strategies Illinois Undertaking field visits Missouri Contacting DOT staff New Jersey Reviewing video-logs New York Reviewing video-logs Pennsylvania Reviewing video-logs and contacting DOT staff Wisconsin Contacting DOT staff TABLE 3-22 Percentage of two-lane treatment sites with and without illumination State % with presence of illumination % without presence of illumination Illinois 7.1 92.9 New Jersey 42.0 58.0 New York 26.0 74.0 Pennsylvania 0.0 100.0 TABLE 3-23 Percentage of two-lane treatment sites with and without additional delineation (chevrons or post-mounted delineators) State % with additional delineation % without additional delineation Illinois 1.0 99.0 New Jersey 1.0 99.0 New York 26.0 74.0 Pennsylvania 7.4 92.6 State % with rumble strips % without rumble strips Illinois 0.0 100.0 New Jersey 0.0 100.0 New York 0.0 100.0 Pennsylvania 6.6 93.4 State % with rumble strips % without rumble strips Missouri 53.1 46.9 New York 63.3 36.7 Pennsylvania 37.7 62.3 Wisconsin 100.0 0.0 State % with rumble strips % without rumble strips Pennsylvania 21 79 Wisconsin 100 0 TABLE 3-24 Percentage of two-lane treatment sites with and without shoulder rumble strips TABLE 3-25 Percentage of four-lane freeway treatment sites with and without shoulder rumble strips TABLE 3-26 Percentage of four-lane expressway treatment sites with and without shoulder rumble strips State % of total roadway length (urban) % of total roadway length (rural) Pennsylvania 18.6 81.4 Wisconsin 11.6 88.4 TABLE 3-19 Summary information: environment type at four-lane expressway treatment sites State Information Received Source Illinois AADTs for 1991, 1992, 1994, and 1997 to 2000 Highway Safety Information System (HSIS) Missouri AADTs for 1991 to 2001 Missouri DOT New Jersey Short-term counting station data (downloaded from Internet)—various years New Jersey DOT New York AADTs for 1991 to 2001 New York DOT Pennsylvania AADTs for 1991 to 2001 Pennsylvania DOT Wisconsin Traffic count books for 1995, 1997, and 2000 Wisconsin DOT TABLE 3-20 AADT data and sources

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 518: Safety Evaluation of Permanent Raised Pavement Markers examines the safety performance of snowplowable permanent raised pavement markers on two-lane roadways and four-lane freeways.

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