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From page 71... ... NCHRP 3-78b: Final Project Report April 2016 71 5 MODELING AND APPLICATIONS This chapter presents an overview of nine of the methodological steps from the crossing assessment methodology shown in Chapter 7 of the NCHRP 03-78b guidebook. A list of these models is presented in Table 5-1, followed by more detailed discussion. Read the entire page →
From page 72... ... NCHRP 3-78b: Final Project Report April 2016 72 Figure 5-1: Roundabout Vehicle Path Radii (Source: NCHRP Report 672) At a roundabout entry, this speed is principally a function of the R1 radius shown in Figure 5-1. Read the entire page →
From page 73... ... NCHRP 3-78b: Final Project Report April 2016 73 Figure 5-2: Free-Flow Speed Model Validation with Field Data The figure shows a data plot with fastest path radius (in feet) on the x-axis and vehicle speed (in mi/h) Read the entire page →
From page 74... ... NCHRP 3-78b: Final Project Report April 2016 74 the presence of conflicting vehicular traffic and determine crossing opportunities at intersections and roundabouts. The distance is established through sight triangles that allow a pedestrian to evaluate potential conflicts with approaching vehicles. Read the entire page →
From page 75... ... NCHRP 3-78b: Final Project Report April 2016 75 the splitter island; and • Entering traffic is decelerating as drivers approach the yield line and circular roadway, while exiting traffic is accelerating as drivers exit the roundabout. Since traffic patterns at each conflicting approach are judged independently, there are sight distances and sight triangles associated with each location and their conflicting approaches. Read the entire page →
From page 76... ... NCHRP 3-78b: Final Project Report April 2016 76 d4 = distance along entry leg upstream of the entry crosswalk for crossing from island, ft; Vn,stream = design speed of conflicting movement, mph; tn,c = critical headway required by a pedestrian crossing a specific traffic stream, depends on the number of lanes and lane width. Once the minimum distance, d, is determined for all possible conflicting movements, the designer should plot the distance along the actual vehicle path that is driven (i.e. Read the entire page →
From page 77... ... NCHRP 3-78b: Final Project Report April 2016 77 Figure 5-4: Pedestrian Sight Triangles for each Crossing Location (Sidewalk and crosswalks will be added to this figure) This figure shows a schematic of a roundabout with estimated sight triangles drawn based on the calculated sight distances. Read the entire page →
From page 78... ... NCHRP 3-78b: Final Project Report April 2016 78 roundabout (CTL with a downstream acceleration lane) Read the entire page →
From page 79... ... Figure 5-6: Sight Triangles Associated with Crossing Locations at CTLs This figure shows a schematic of a CTL with estimated sight triangles drawn based on the calculated sight distances. Sight triangles are drawn for both crossings from the curb and crossings from the splitter island. Read the entire page →
From page 80... ... 80 NCHRP 3-78b: Final Project Report April 2016 (May 1990) Read the entire page →
From page 81... ... 81 NCHRP 3-78b: Final Project Report April 2016 Figure 5-7: Gap Opportunity Validation for Roundabout Entry and Exit The figure shows a data plot with traffic volume on the studied roundabout approach (in vehicles per hour) on the x-axis and gap opportunities (in %) Read the entire page →
From page 82... ... 82 NCHRP 3-78b: Final Project Report April 2016 Figure 5-8: Gap Opportunity Validation for Channelized Turn Lanes The figure shows a data plot with traffic volume on the studied roundabout approach (in vehicles per hour) on the x-axis and gap opportunities (in %) Read the entire page →
From page 83... ... 83 NCHRP 3-78b: Final Project Report April 2016 the presence of pedestrians, including university campuses and downtown areas. Most field studies estimate the probability of yielding based on the number of vehicles that could have yielded, P(Yield) Read the entire page →
From page 84... ... 84 NCHRP 3-78b: Final Project Report April 2016 Table 5-3: Recommended Model to Predict Yielding Rates to Pedestrians YIELDR Regression Coefficient Std Error p 95% Conf Interval RDS -0.065 0.011 0.000* Read the entire page →
From page 85... ... 85 NCHRP 3-78b: Final Project Report April 2016 Figure 5-9: Graphical Representation of Yield Probability Model 5.5 Gap Utilization Model This model describes the gap acceptance behavior by blind pedestrians at roundabouts and intersections with CTLs. It is hypothesized that the gap utilization rate is primarily a function of the size of the available gaps, and further that gaps needed by blind travelers are likely to be longer than those needed by sighted pedestrians (as described in the gap opportunity model) Read the entire page →
From page 86... ... 86 NCHRP 3-78b: Final Project Report April 2016 There is presently insufficient data in the literature to derive more sophisticated gap utilization models, but analysts are encouraged to use local data or estimates should those be available. The observed averages and standard error of gap utilization are shown graphically in Figure 5-10. Read the entire page →
From page 87... ... 87 NCHRP 3-78b: Final Project Report April 2016 The table shows average yield utilization rates for all roundabout sites in the range of 60-80%. For CTLs, the yield utilization was found to be much lower on average at around 35%, which is likely explained by increased background noise at many CTL locations. Read the entire page →
From page 88... ... 88 NCHRP 3-78b: Final Project Report April 2016 The first and foremost audibility consideration is the location of the crosswalk relative to sources of noise. In the case of a CTL, the majority of traffic noise is generated at the main intersection. Read the entire page →
From page 89... ... 89 NCHRP 3-78b: Final Project Report April 2016 crosswalk located in a downhill portion may provide better acoustic information about an approaching vehicle than a crosswalk approached in an uphill section. This pattern was suggested by research performed at two CTLs on opposing approaches at a signalized intersection described in NCHRP Report 674. Read the entire page →
From page 90... ... 90 NCHRP 3-78b: Final Project Report April 2016 sighted pedestrians, who may be presented with the same gap and yield opportunities, but have different rates of utilizing these opportunities. Three separate models are developed for single-lane CTL approaches, single-lane roundabout approaches, and two-lane roundabout approaches. Read the entire page →
From page 91... ... 91 NCHRP 3-78b: Final Project Report April 2016 Figure 5-12: Graphical Representation of CTL Delay Model Figure 5-13: Graphical Representation of Single-Lane RBT Delay Model Read the entire page →
From page 92... ... 92 NCHRP 3-78b: Final Project Report April 2016 Figure 5-14: Graphical Representation of Two-Lane RBT Delay Model As an alternative to this pedestrian delay methodology, the analyst may choose to refer to the method in the Highway Capacity Manual, or conduct a simulation study. However, it is emphasized here that the HCM method does not account for opportunity utilization of less than 100%. Read the entire page →
From page 93... ... 93 NCHRP 3-78b: Final Project Report April 2016 P(INT) Read the entire page →
From page 94... ... 94 NCHRP 3-78b: Final Project Report April 2016 -- - This page intentionally left blank -- - Read the entire page →

From page 71...

... NCHRP 3-78b: Final Project Report April 2016 71 5 MODELING AND APPLICATIONS This chapter presents an overview of nine of the methodological steps from the crossing assessment methodology shown in Chapter 7 of the NCHRP 03-78b guidebook. A list of these models is presented in Table 5-1, followed by more detailed discussion.