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From page 7... ... NCHRP 17-59 7 CHAPTER 2: RESEARCH APPROACH/ANALYTICAL METHODOLOGY OVERVIEW Chapter 2 presents the review of existing intersection sight distance (ISD) practices and relationships. Read the entire page →
From page 8... ... NCHRP 17-59 8 Traffic Volume As with most safety performance research, most crash-based evaluations indicate that traffic volume is highly correlated with crash occurrence. Two relevant studies were reviewed that have attempted to relate traffic volumes and intersection sight distance to roadway safety. Read the entire page →
From page 9... ... NCHRP 17-59 9 (ANOVA) was used for the statistical analysis. Read the entire page →
From page 10... ... NCHRP 17-59 10 Conflicting conclusions regarding the safety effectiveness of adequate ISD in rural areas were evident in some research. Charlton (2003) Read the entire page →
From page 11... ... NCHRP 17-59 11 etc.) between 1988 and 1992. Read the entire page →
From page 12... ... NCHRP 17-59 12 Over 200 intersections in both Michigan and California were selected based on the following constraints:  Three-leg rural intersections, major road four-lane, minor leg two-lane stop-controlled, median width less than or equal to 36 feet on major road.  Four-leg rural intersections, major road four-lane, minor legs two-lane stop-controlled, median width less than or equal to 36 feet on major road. Read the entire page →
From page 13... ... NCHRP 17-59 13 between intersection sight distance and speed. Therefore, visibility was measured in time instead of distance in the model, which was accomplished by dividing the sight distance by speed on the approach. Read the entire page →
From page 14... ... NCHRP 17-59 14 Collection of State and Local Policies The project team collected policies that were readily available, either in the literature or on state and local transportation websites. The original intention of the research was to conduct a survey of agencies. Read the entire page →
From page 15... ... NCHRP 17-59 15 Each of the collected policies was reviewed to answer the following questions: 1. Field Method a. Read the entire page →
From page 16... ... NCHRP 17-59 16 Table 2. Summary of Field Method. Read the entire page →
From page 17... ... NCHRP 17-59 17 Sources Equipment Used in the Field Number of Staff Notes Highway Safety Investigation Manual for the Oregon Department of Transportation, Oregon DOT, Traffic-Roadway Section Unroll measuring tape(3.5') at DP, unroll measuring tape (3.5') Read the entire page →
From page 18... ... NCHRP 17-59 18 Table 3. Summary of Parameters. Read the entire page →
From page 19... ... NCHRP 17-59 19 Sources Driver's Eye Height Object Height Decision Point (DP) Position Critical Point (CP) Read the entire page →
From page 20... ... NCHRP 17-59 20 Sources Driver's Eye Height Object Height Decision Point (DP) Position Critical Point (CP) Read the entire page →
From page 21... ... NCHRP 17-59 21 Sources Driver's Eye Height Object Height Decision Point (DP) Position Critical Point (CP) Read the entire page →
From page 22... ... NCHRP 17-59 22 Table 4. Summary of Other Policy Specifics. Read the entire page →
From page 23... ... NCHRP 17-59 23 Sources Determination of Major Road Design Speed Presence of Countermeasures in Manual Notable Items Traffic Safety Manual, Bonne County, MO Not specified Install warning signs Different stopping sight distances for different ADTs Sight Distance Regulations, City of Wheat Ridge, CO Not specified No Illinois' Bureau of Local Roads and Streets Manual, Illinois DOT, Division of Highways Not specified Provide traffic control devices; Design applications; Remove obstructions Values of ISD correspond to the AASHTO standard of a 7.5 sec gap Highway Safety Investigation Manual for the Oregon Department of Transportation, Oregon DOT, Traffic-Roadway Section Approach speed measured at 250 ft from the intersection Improve approach visibility; Prohibit parking; Remove obstacles; Install warning signs; Reduce speed limit on approaches 1) Visibility Check 2) Read the entire page →
From page 24... ... NCHRP 17-59 24 Summary of Field Methods The collected policies were reviewed to determine the methods used in the field, including equipment, staffing, and protocol used to collect ISD in the field. The majority of the policies did not specify a method. Read the entire page →
From page 25... ... NCHRP 17-59 25 should be located at the center of the approaching lane, and two of the policies require a lateral offset of 4 feet or 5 feet from the centerline of the roadway. The review also revealed that the location of the stop bar has limited consideration in the selection of the DP position; with only one policy instructing that the DP should be located 10 feet back from the stop bar or aligned with the stop sign. Read the entire page →
From page 26... ... NCHRP 17-59 26 Five of the reviewed policies identified countermeasures that should be considered for deficient sight distance. The treatments include: (1) Read the entire page →
From page 27... ... NCHRP 17-59 27 level of driver understanding of this basic rule is likely correlated with driver familiarity/experience with uncontrolled intersections. Furthermore, engineers must also consider that uncontrolled intersections lack visual cues from traffic control devices indicating the need to stop, which suggests utilizing conservative designs. Read the entire page →
From page 28... ... NCHRP 17-59 28 Prior to the 2001 Green Book, the AASHTO method for determining the required approach ISD for uncontrolled intersections (termed "Case 1" in the 1994 and prior Green Books) was determined based on providing adequate sight distance for drivers on both approaches to adjust speed – but not stop (AASHTO 1994) Read the entire page →
From page 29... ... NCHRP 17-59 29 necessarily accommodated by the sight triangle. However, sight triangles of such magnitude are neither practical nor necessary for typical low volume roadways where uncontrolled intersections are most common. Read the entire page →
From page 30... ... NCHRP F Discussio The ISD Green Bo than the s underesti or less. R and rema importan follows:  In m (A sp R m  In 5 un ut re 17-59 igure 1. Read the entire page →
From page 31... ... NCHRP 17-59 31 are correlated with the frequency with which vehicles on the intersecting roadway are present. Specifically, drivers typically show less of a speed reduction at locations when low volumes are present on the intersecting roadway, in many cases exceeding the safe approach speed. Read the entire page →
From page 32... ... NCHRP 17-59 32  Skew angle: Current AASHTO method recommends against using no traffic control at intersections with oblique angles. Recommendation: Intersections with oblique angles should not be left uncontrolled. Read the entire page →
From page 33... ... NCHRP 17-59 33 sites. Once the corridor was identified, the project team checked the traffic control type and number of lanes on the minor road for each intersection along the corridor using Google Earth. Read the entire page →
From page 34... ... NCHRP 17-59 Figure 2. Figu Data Collec re 3. Read the entire page →
From page 35... ... NCHRP Data Co Table 5 p were iden required Required their inco elements by allowi are defin each stud office) Read the entire page →
From page 36... ... NCHRP 17-59 36 Table 5. Crash, Roadway, and Traffic/Operations Data Elements of Interest. Read the entire page →
From page 37... ... NCHRP 17-59 37 Data Type Data Element Require/ Desire Description/Comment Data Sources Shoulder width Des. Width of paved shoulder in feet Field(NC) Read the entire page →
From page 38... ... NCHRP 17-59 38 Data Type Data Element Require/ Desire Description/Comment Data Sources Intersection angle Des. Approximate angle between major road and approach of interest Google Earth Presence of on-street parking Des. Read the entire page →
From page 39... ... NCHRP 17-59 39 Crash Data Four years of crash data were compiled from HSIS accident and vehicle files (i.e., 2008-2011 in OH and WA, 2009-2012 in NC) Read the entire page →
From page 40... ... NCHRP 17-59 40 Table 6. Combination of Maneuvers. Read the entire page →
From page 41... ... NCHRP Using the was trave informati  If ca ro  If ca ro In the en values of represent Assessme An explo results of sight for driver in number o 17-59 vehicle tra ling on the on, the cras the major r tegorized a adway and the major r tegorized a adway and d, this appro an approach s the target nt of Interse ratory comp the literatur the minor ro appropriate f point obje Figure 5. L vel direction major road a h, roadway, oad vehicle s a right-dire traffic data a oad vehicle s a left-direc traffic data f ach resulted level ISD crash freque ction Sight onent of thi e review, th ad driver co gap selectio cts on the ne eft- and Rig data, the pr nd which v and traffic d was travelin ctional targ ssociated w was travelin tional target or the left-d in target cr (i.e., one ob ncy for one Distance Qu s study is th e project tea uld play eith n. Read the entire page →
From page 42... ... NCHRP 17-59 42 data, the NCHRP project panel suggested eliminating collecting this data element. Instead the panel directed the project team took a more subjective approach to appraising ISD quality -- one that was more qualitative in nature -- to explore the hypothesis that this has an impact on safety To develop this subjective approach, the team hypothesized that discrete roadside objects (e.g. Read the entire page →
From page 43... ... NCHRP 17-59 Fig Fig ure 6. Read the entire page →
From page 44... ... NCHRP Field Co The field foliage is sighting p measurem  T th  T gr The proje Final App Selection at each si Green Bo was base ISD mea The Gree through l the mino minor roa entering 17-59 llection of A measureme robust) Read the entire page →
From page 45... ... NCHRP the drive reason, th Equipme road DPs used to d  T an sc li si  T sl m ab h fr in A it th Procedur away fro the neare this unsa when the the range between between horizonta measurin Based ini project te available than or e "1,321 fe 17-59 r selected D e project te nt: A sighti looking in etermine the he rangefind d was moun ope was 42 mits the imp ghting perso he target con ow moving etal pole su ove the gro as sufficient om the rang creases its c dditionally, em at nation e target wil e: The runn m the DP, id st travel lan fe and then t full metal t finder's sco the CP and D the CP and t l curves or g wheel to d tial field me am used 1,3 ISD. There qual to 1,320 et" to indica P was the sa am determin ng height of each directio limits of av er includes ted on top o in. Read the entire page →
From page 46... ... NCHRP 17-59 46 Summary of Selected Sites Data were ultimately collected at a total of 832 stop-controlled approaches. Table 8 displays general characteristics of the sites that were ultimately selected for data collection, stratified by state, area type, and terrain. Read the entire page →
From page 47... ... NCHRP 17-59 47 Table 10. Target Stratified by State and Year. Read the entire page →
From page 48... ... NCHRP 17-59 48 Table 11. Summary Statistics for NC Continuous Independent Variables. Read the entire page →
From page 49... ... NCHRP 17-59 49 Table 12. Summary Statistics for NC Categorical Independent Variables. Read the entire page →
From page 50... ... NCHRP 17-59 50 Variable Name Variable Description Proportion Minclass Minor route is classified as principal arterial (Minparterial) 0.3 % Minor route is classified as major arterial (Minmajarterial) Read the entire page →
From page 51... ... NCHRP 17-59 51 Table 13. Summary Statistics for OH Continuous Independent Variables. Read the entire page →
From page 52... ... NCHRP 17-59 52 Table 14. Summary Statistics for OH Categorical Independent Variables. Read the entire page →
From page 53... ... NCHRP 17-59 53 Variable Name Variable Description Proportion Minclass Minor route is classified as principal arterial (Minparterial) 0.0 % Minor route is classified as major arterial (Minmajarterial) Read the entire page →
From page 54... ... NCHRP 17-59 54 Table 15. Summary Statistics for WA Continuous Independent Variables. Read the entire page →
From page 55... ... NCHRP 17-59 55 Table 16. Summary Statistics for WA Categorical Independent Variables. Read the entire page →
From page 56... ... NCHRP 17-59 56 Variable Name Variable Description Proportion Minclass Minor route is classified as principal arterial (Minparterial) 1.9 % Minor route is classified as major arterial (Minmajarterial) Read the entire page →
From page 57... ... NCHRP 17-59 57 The current state-of-the-practice for developing statistical road safety models of this type is to assume a log-linear relationship between expected crash frequency and site characteristics. Generalized Linear Modeling (GLM) Read the entire page →
From page 58... ... NCHRP 17-59 58  The impact of ISD on target crashes and target fatal and injury crashes is also expected to vary with major and minor road traffic volumes. Variables that capture volume and ISD interactions are needed to capture these effects. Read the entire page →

From page 7...

... NCHRP 17-59 7 CHAPTER 2: RESEARCH APPROACH/ANALYTICAL METHODOLOGY OVERVIEW Chapter 2 presents the review of existing intersection sight distance (ISD) practices and relationships.