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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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Suggested Citation:"11 Appendix D: Crossing Sight Distance Details." National Academies of Sciences, Engineering, and Medicine. 2016. Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. Washington, DC: The National Academies Press. doi: 10.17226/24675.
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NCHRP 3-78b: Final Project Report April 2016 137 11 APPENDIX D: CROSSING SIGHT DISTANCE DETAILS 11.1 Introduction This report presents the results of research to develop guidance for designing crosswalks at modern roundabout and channelized turn lanes (CLTs) to assist pedestrians with vision disabilities. The issues of pedestrian behavior and safety at roundabout crosswalks are not well understood, particularly for pedestrians with sensory or mobility impairments. A previous study shows that blind pedestrians miss more crossing opportunities and make riskier judgments than sighted pedestrians (Ashmead et al., 2005). The main considerations include the driver sight distance needs toward the conflicting traffic stream (roundabout circle and channelized turn lane downstream traffic), as well as sight distances toward a pedestrian waiting on the curb or on a splitter island. The purpose of this research is to come up with the recommended design that can minimize vehicular speed, while maximizing sight distances to the crosswalk, so that no (additional) treatment may be necessary. This report documents and presents the results of research to develop guidance for the application of crossing solutions at roundabout and channelized turn lanes and later in this report the alternative approaches for designing an applicable pedestrian crossing sight distance will be discussed. The issue of pedestrian safety at roundabout crosswalks remains generally unstudied. Because blind pedestrians cannot use visual information to identify approaching vehicles and to make crossing decisions at traditional intersections, they typically rely on predictable patterns of vehicle movement that are usually created by traffic control devices. At modern roundabout intersections, these techniques for making non- visual street-crossing judgments are not useful because traffic flows unpredictably in and out of the roundabout (Retting et al., 2001). Channelized turn lanes (CTLs) are a common treatment applicable for signalized intersections with high volumes of right-turning vehicles that experience excessive delay due to traffic signals; they allow heavy right-turning movement to bypass the main intersection (FHWA, 2000). Larger turn radii and higher speeds are a safety issue for pedestrians. Channelized turn lanes resemble roundabouts in geometry and pose similar challenges to blind pedestrians attempting to cross the road. In both designs, traffic may be free flowing or may yield to circulating vehicles at roundabouts or to downstream traffic at CTLs. Crosswalks at CTLs are usually unsignalized. The review of the literature confirmed that pedestrian crossing sight distance has not been explored to the same degree that vehicle sight distance has been investigated. While similar in concept, there are a variety of pedestrian characteristics, site geometry, and crosswalk location that require separate crossing sight distance design procedures. In the AASHTO publication, A Policy on the Geometric Design of Highways and Streets, also known as the “Green Book,” many design principles are based on the concept of vehicle sight distance calculations. In details, AASHTO distinguishes three types of sight distance: (1) stopping sight distance, (2) intersection sight distance, and (3) decision sight distance. These sight distances are used to guide the design of features such as minimum radii for horizontal and vertical curves, or to limit landscaping and sight obstructions at intersections and serve to reduce impedances to the driver’s line of sight (AASHTO, 2011). The resulting design principles are also reflected in roundabout design guidelines (Rodegerdts et al., 2010), and apply equally to CTLs. Pedestrian sight distance is currently not considered in the Green Book. 11.2 Methodology For the purpose of this research, the methodology developed to determine crossing sight distance adequacy at a roundabout and CTLs has been adapted from the sight distance performance check for vehicles at roundabouts from NCHRP Report 672: Roundabouts: An Informational Guide (Rodegerdts et al., 2010), calculations and definitions from the AASHTO “Green Book” (AASHTO, 2011), and

NCHRP 3-78b: Final Project Report April 2016 138 roundabout segment methodology in Chapter 30 of the 2010 Highway Capacity Manual (TRB, 2010). In this report of the results of research under NCHRP 3-78b, crossing sight distance is introduced as the distance required by pedestrians to recognize the presence of conflicting vehicular traffic and determine crossing opportunities at intersections and roundabouts. The estimation of crossing sight distance requires several input variables and assumptions to perform the calculations. First, the calculation requires the estimation of a prevailing vehicle speed. This speed is estimated from site geometry (design radii), as well as speed prediction equations described in next section. Second, the calculation requires the estimation of a crossable gap time, which is a function of crossing distance, pedestrian walking speed, and any decision latency. For this research, the distance is established through sight triangles that allow a pedestrian to evaluate potential conflicts with approaching vehicles. Similarly, the resulting sight triangles also assure that the driver has a clear view of a pedestrian waiting to cross or approaching the crosswalk. For pedestrians who are blind, the crossing sight distance applies in that any visual obstructions are also expected to impact the ability to hear approaching vehicles without sound obstructions or deflections. Although sight triangles are traditionally bound by linear vehicle paths, the roadway geometry of roundabouts and CTLs is non-linear as illustrated in Figure 11-1. Figure 11-1: Pedestrian Sight Triangles for Each Crossing Location Therefore, sight distances are derived along the curvature of conflicting vehicular travel paths using the estimated vehicle speed and crossable gap times. This provides the distance for vehicles to travel along a path toward the crosswalk at their current speed in the amount of time needed for a pedestrian to cross the road safely. In other words, adequate crossing sight distance assures that a pedestrian can identify vehicles far enough away to provide sufficient time to cross the road. Adequate crossing sight distance also ensures that drivers can see pedestrians as they step off the curb and into the roadway with sufficient time to react. It also ensures that pedestrians who are blind, who have unimpaired hearing, are likely to be able to hear approaching vehicles well enough to make safe judgments regarding when to begin crossing. 11.3 Data Collection The research team evaluated a list of potential study sites and selected those that were deemed suitable for further field investigation. Under the support of NCHRP 3-78B, the team proposed the application of a

NCHRP 3-78b: Final Project Report April 2016 139 newly developed study protocol--enhanced based on the lessons learned in NCHRP 3-78A. Through studies conducted in this research, and supported by earlier accessibility work, this team sought to identify what aspects of geometry contribute to enhanced accessibility, and to document these findings. Examples include the inscribed diameter, R1 through R5 radii of a roundabout as described in NCHRP Report 672, the relative location of the crosswalk to the circulating lane, the shape of the splitter island at a channelized turn lane, and the curve radii in that channelized turn lane. In addition to geometry audits, the team performed speed studies of free-flow vehicles entering and exiting the roundabout to gain insight on the expected speed patterns in the vicinity of the crosswalk, and the effectiveness of design features (such as RCW) to reduce speeds. With the timing of this project, there was a unique opportunity to study the availability of existing treatments in addition to non-treatment sites across the country for an efficient and timely completion of data collection 11.4 Data Analysis and Framework This section describes the data and geometry analysis of the RBT and CTL sites. As mentioned in previous sections of this report, the method and equations that were used for calculation of crossing sight distance are adopted from AASHTO, NCHRP Report 672, and HCM 2010. The concept and detailed calculation approaches of crossing sight distance for all the study sites is discussed in the following sections. 11.4.1 Approach 1: HCM Gap Acceptance Methodology In our first approach to calculate the minimum intersection sight distance, two parameters were measured based on the collected data from the study fields. The first parameter is the critical headway, tn,c, for the pedestrian. The critical headway describes the minimum amount of time necessary for a pedestrian to cross the roadway. The critical headway calculation is directly derived from the pedestrian analysis method covered in the two-way stop-controlled intersection methodology of the Highway Capacity Manual 2010 (TRB, 2010). tn,c = (Ln / Sp) + ts Where, Ln = crosswalk length for a specific traffic stream, ft; Sp = average pedestrian walking speed, ft/s, could be measured in the field with a maximum value of 3.5 ft/s; ts = pedestrian start-up time and end clearance time, s. In the context of this analysis, the pedestrian start-up and end clearance time estimate should include any decision latency by a blind pedestrian. In field observations and direct comparisons of decision-making by blind and sighted pedestrians at CTLs (Schroeder et al., 2006), it is evident that a sighted person makes the crossing decision much more quickly compared to a blind person, who typically waits for the vehicle sound to subside before making a decision. The second parameter is the vehicle speed. The analyst can either measure or make an assumption about the speed, V, of vehicles along the approach of interest. Using the speed (V) and critical pedestrian headways (tn,c), the length of the conflicting vehicle paths (d) are calculated using the equations below. d1 = (1.467) (V1,entering) (t1,c) d2,e = (1.467) (V2,entering) (t2,c) d2,c = (1.467) (V2,circulating) (t2,c)

NCHRP 3-78b: Final Project Report April 2016 140 d3,e = (1.467) (V3,entering) (t3,c) d3,c = (1.467) (V3,circulating) (t3,c) d4 = (1.467) (V4,entering) (t4,c) Where, d1 = distance along entry leg upstream of the entry crosswalk for crossing from curb, ft; d2,e = distance along previous entry upstream of the exit crosswalk for crossing from island, ft; d2,c = distance along circulating lane upstream of the exit crosswalk for crossing from island, ft; d3,e = distance along previous entry upstream of the exit crosswalk for crossing from curb, ft; d3,c = distance along circulating lane upstream of the exit crosswalk for crossing from curb, ft; 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. Figure 11-2 shows the necessary sight distance, d, for each crossing location at the entry and exit of a roundabout (NCHRP 3-78b) Figure 11-2: Minimum Sight Distance Along the Actual Path Because pedestrians crossing at CTLs are conceptually similar to those crossing at roundabouts, the same parameters of critical headway and vehicle speed were measured using the aforementioned equations for the distance along the approach upstream of the crosswalk for crossing from curb at CTLs. In this step, necessary sight distance was measured using the existing geometric measurement and 85 percentile and average speed collected from the filed study. The team assumed 3.5 feet per second walking speed and 2 second lost time. Figure 11-3 shows the calculated sight distance, d, for each crossing location at the entry and exit for the Cemetery Road and Main Street roundabout in Hilliard, OH.

NCHRP 3-78b: Final Project Report April 2016 141 tn,c = (Ln / Sp) + ts Sight Distance (Avg Speed) Sight Distance (85% Speed) Crosswalk Length, ft (Ln) Sp (f t/sec) ts (sec) Critical Headway (tn,c) Avg Speed (mph) 85 % Speed (mph) d1 = (1.467) (V1,entering) (t1,c) 288 263 26 3.5 2 9.43 20.8 19 d2,e = (1.467) (V2,entering) (t2,c) 206 302 23 3.5 2 8.57 16.4 24 d2,c = (1.467) (V2,circulating) (t2,c) 262 302 23 3.5 2 8.57 20.8 24 d3,e = (1.467) (V3,entering) (t3,c) 201 227 21.5 3.5 2 8.14 16.8 19 d3,c = (1.467) (V3,circulating) (t3,c) 201 227 21.5 3.5 2 8.14 16.8 19 d4 = (1.467) (V4,entering) (t4,c) 331 386 24 3.5 2 8.86 25.5 29.7 Figure 11-3: West Approach at Cemetery Road at Main Street, Hilliard, OH After applying this method to all the roundabouts and CTLs locations, the team observed longer sight distances than they expected. The team decided to use a different approach for further analysis. 11.4.2 Approach 2 The team proposed a second, alternative approach to calculate the crossing sight distance that was based on a variation of stopping sight distance as presented AASHTO “Green Book.” For each approach, the team calculated five crossing sight distances using the same equations used in the previous method and checked which method would give us the minimum distance. These methods are as follows: 1. Gap Acceptance Distance, Full Crossing Width, 2-second reaction time 2. Gap Acceptance Distance, Full Crossing Width, 0-second reaction time 3. Gap Acceptance Distance, Crossing Width minus 1/2 lane, 0-second reaction time 4. Yield Reaction Distance, 5 second deceleration, 2.5 second reaction time 5. Yield Reaction Distance, 5 second deceleration, 1 second reaction time The average collected field speed and the existing geometric measurement were used in this step. Figure 11-4 shows the calculated sight distance, d, for each approach, entry and exit, at the Cemetery Road and Main Street roundabout in Hilliard, OH.

NCHRP 3-78b: Final Project Report April 2016 142 Entry d C1 d C2 d C3 Entry d C4 d C5 Reaction Time (sec) 2 0 0 Reaction Time (sec) 1 2.5 Crossing Width (ft) 24 24 18 Deceleration Rate (ft/s^2) 5 5 Vehicle Speed (mph) Gap Acceptance Distance (ft) Vehicle Speed (mph) Yield Reaction Distance (ft) 16.8 219 169 127 16.8 55 92 Exit d C1 d C2 d C3 Exit d C4 d C5 Reaction Time (sec) 2 0 0 Reaction Time (sec) 1 2.5 Crossing Width (ft) 22 22 16.5 Deceleration Rate (ft/s^2) 5 5 Vehicle Speed (mph) Gap Acceptance Distance (ft) Vehicle Speed (mph) Yield Reaction Distance (ft) 25.5 311 236 177 25.5 107 164 Figure 11-4: West and East Approach at Cemetery Road at Main Street, Hilliard, OH The same parameters of critical headway and vehicle speed were measured using the aforementioned equations for the distance along the approach upstream of the crosswalk for crossing from curb at CTLs . 11.4.3 Approach 3: Fastest Path Method In this approach, speeds were predicted using the fastest path method presented in NCHRP Report 672. The fastest path is the smoothest and flattest path possible for a single vehicle ignoring all the lane markings and in the absence of other vehicles. In NCHRP Report 672, the fastest path is described as a path that vehicles travel through the entry, circulating around the center island, and out of the exit. It is important to know that the fastest path methodology does not represent expected vehicle speed, but rather assumed reasonable entry speed for design purposes. The actual speed can be varied based on individual abilities and tolerance for gravitational forces exit (NCHRP 672). Figure 11-5 illustrates the five important path radii that were checked and measured in this approach. R1, is the entry path radius and the minimum radius on the fastest through path prior to the entrance line. R2, is the circulating path radius and the minimum radius on the fastest through path around the central island. R3, is the exit path radius and the minimum radius on the fastest through path into the exit. R4, is the left-turn path radius and the minimum radius on the path of the conflicting left-turn movement. R5 is the right turn path radius and the minimum radius on

NCHRP 3-78b: Final Project Report April 2016 143 the fastest path of a right-turning vehicle. These radii paths are not the same as the curb radii path and R1 through R5 measured using the vehicle centerline in its path through the roundabout. Figure 11-5: Fastest Path Illustration (NCHRP 672) The radii paths were measured using AutoCAD software by drawing a fitted curve along each path for entry, exiting, and circulating movements. All these radii path measurements were used to predict speed using the following equations that were adopted by AASHTO “Green Book” and presented in NCHRP 672. V = 3.4415R0.3861 , for e = + 0.02 V = 3.4614R0.3673 , for e = - 0.02 Where; V = predicted speed, mph; R = radius of curve, ft; and e = superelevation, ft/ft. These equations were used only to estimate the entry vehicle speed (V1), exiting speed (V3), and right turn speed at the roundabout. In order to calculate the circulating speed (V2) and (V4), the circulating path radius (R2) and the left-turn path radius (R4) were calculated using equation presented in HCH 2010 Chapter 30. Where: rc,th = average radius of circulating path of through movement (ft),

NCHRP 3-78b: Final Project Report April 2016 144 ICD = inscribed circle diameter (ft), Nc = number of circulating lane(s), and wc = average width of circulating lane(s) (ft). This equation provided the average radius of circulating path by assuming that the radius of circulating path occupies the centerline of the circulating roadway is equal to half of the central island plus half of the total width of the circulatory roadway. The center line path was measured around the circular movement and, for the ease of calculation, the second parameter in the calculation was not used in our measurement. The speeds associated with this radius for circulating movement were calculated from the following equation from NCHRP Report 572, which assumes a negative cross slope of the circulatory roadway of - 0.02. Where: Sc = circulating speed (mi/h), and rc,th = average radius of circulating path of through movement (ft). To better predict actual entry speeds, the following equation was used for deceleration of vehicles from the entering R1 speed to the circulating R2 speed. Using a deceleration factor would promote a safe design by controlling entry speed. This equation was provided in NCHRP Report 672. Where: V1 = entry speed, mph; V1pbase = V1 speed predicted based on path radius, mph; V2 = circulatory speed for through vehicles predicted based on path radius, mph; a12 = deceleration between the point of interest along V1 path and the midpoint of V2 path = 4.2 ft/s2; and d12 = distance along the vehicle path between the point of interest along V1 path and the midpoint of V2 path, ft. A similar approach can be used for the exiting speed based on the exit radius R3. At the locations with a large radius exit, the measured R3 can be so large that the acceleration characteristics of the vehicle will govern the actual speeds that can be achieved. To control the exit speed, the following equation was used from NCHRP Report 672; Where;

NCHRP 3-78b: Final Project Report April 2016 145 V3 = exit speed, mph; V3pbase = V3 speed predicted based on path radius, mph; V2 = circulatory speed for through vehicles predicted based on path radius, mph; a23 = acceleration between the midpoint of V2 path and the point of interest along V3 path = 6.9 ft/s2; and d23 = distance along the vehicle path between midpoint of V2 path and point of interest along V3 path, ft. After estimating the speed for all the movements along each path and in order to obtain the through and left-turn movement speed, the average of total speed for entry and circulating vehicle (V2+V3+V4/3) were measured. The result of this approach is shown in Table 11-1. Like the first method described in this chapter, we assumed 3.5 feet per second walking speed and 2 second reaction time. Table 11-1: Results of Sight Distance Calculation (Novi, MI) Maple Rd and Farmington Rd., Novi, MI East Exit (L & T) East Exit (R) East Entry North Exit (L & T) North Exit (R) South Entry R1 118 - 184 99 - 150 R2 & R4 104 - 104 104 - 104 R3 122 - - 113 - - R5 - 166 - - 105 - Reaction Time (sec) 2 2 2 2 2 2 Crossing Width (ft) 36 36 32 23 23 21 Vehicle Speed (mph) 21 24 25 21 20 23 Gap Acceptance Distance (ft) 372 433 410 260 252 270 This equation generally provides a reasonable prediction for the left- turn and through movement circulating speed. Because the presence of raised crosswalks (RCW) in some of the study sites could govern the speed that can be reached at the entry and the exit, we measured and recalculated the crossing sight distance using a new approach. The three estimated speeds based on the fastest path method, deceleration/acceleration, and observed speed effect by raised cross walk were compared and the minimum of these three speeds was selected. Section 11.7 provides an example of this calculation for the sites that have raised crosswalks. The following table shows the new speed estimation for one of the study sites that was impacted by RCW. Table 11-2: Results of Sight Distance Calculation (Novi, MI) Maple Rd and Farmington Rd., Novi, MI East Exit (L & T) East Exit (R) East Entry North Exit (L & T) North Exit (R) South Entry R1 118 - 184 99 - 150 R2 & R4 104 - 104 104 - 104 R3 122 - - 113 - - R5 - 166 - - 105 - Reaction Time (sec) 2 2 2 2 2 2 Crossing Width (ft) 36 36 32 23 23 21 Vehicle Speed (mph) 19 13 13 19 13 13 Gap Acceptance Distance (ft) 336 235 213 235 164 153 This method was also applied to measure CTL crossing sight distance with raised crosswalks. Additional table and sight distance measurements for all other sites presented in Section 11.6 and Section 11.7.

NCHRP 3-78b: Final Project Report April 2016 146 11.5 Summary Summarizing the discussion above, the team proposed a total of 20 sight distance pedestrian approaches to be analyzed for roundabouts and channelized turn lanes, with some of them having treatment installations such as raised crosswalks to reduce the vehicle speed in five different states across the United States. Roundabouts and CTLs present similar challenges to pedestrians who are blind, since they both have yield controlled approaches to the intersection. However, distinct differences in traffic patterns and design and geometric attributes between roundabouts and CTLs result in unique challenges to define these performance checks for each type of facility. The methodology developed to determine crossing sight distance adequacy at a roundabout or CTL was adapted from the sight distance performance check for vehicles at roundabouts. Since there has not been enough study done on the concept of blind pedestrian crossing sight distance, several alternative solutions were tried, and appropriate sight distance measurements that could be recommended as a design guideline for the future construction are proposed. Figure 11-6: Comparison Chart of All Three Approaches (RBT, Novi, MI) As shown in Figure 11-6, the result of measuring fastest path method that was explained previously and considering the existing raised crosswalk effect leads to a lower sight distance path. The resulting finding from the fastest path method gives us a conservative sight distance length that will help pedestrians to determine when to accept the gap and thus will make crossing safer for them.

NCHRP 3-78b: Final Project Report April 2016 147 11.6 Sight Distance Calculation Details Maple Rd and Farmington Rd., Novi, MI Approach Leg: East Exit ICD (ft) R1 R2 R3 R4 R5 d12 d23 251 118 104 122 104 166 180 165 Radius decel accel Field RCW Min V1 21 33 21 V2 (Sc) 20 33 20 V3 21 15 15 V4 20 33 20 V5 24 13 13 T & L 19 R 13 Approach Leg: North Exit ICD (ft) R1 R2 R3 R4 R5 d12 d23 251 99 104 113 104 105 200 165 Radius decel accel Field RCW Min V1 19 35 19 V2 (Sc) 20 33 20 V3 20 15 15 V4 20 33 20 V5 20 13 13 T & L 19 R 13 Approach Leg: South Entry ICD (ft) R1 R2 R3 R4 R5 d12 d23 251 150 104 160 Radius decel accel Field RCW V1 23 32 13 13 V2 (Sc) 20 T 13 Approach Leg: East Entry ICD (ft) R1 R2 R3 R4 R5 d12 d23 251 184 104 180 Radius decel accel Field RCW V1 25 33 13 13 V2 (Sc) 20 T 13

NCHRP 3-78b: Final Project Report April 2016 148 Cherrywood and Greenbelt Metro, Greenbelt MD Approach Leg: West Exit ICD (ft) R1 R2 R3 R4 R5 d12 d23 96 67 40 97 40 86 105 155 V,Radius decel accel Field RCW Min V1 17 25 17 V2 (Sc) 14 31 14 V3 19 16.5 17 V4 14 31 14 V5 18 17 T & L 15 R 17 Approach Leg: West Entry ICD (ft) R1 R2 R3 R4 R5 d12 d23 251 150 104 105 V,Radius decel accel Field RCW Min V1 23 29 17.3 17 V2 (Sc) 20 T 17.3

NCHRP 3-78b: Final Project Report April 2016 149 11.7 Sight Distance Example Application This appendix provides all the final calculations from the “Approach 3” method, and aerial views of all the study sites where calculated sight distance paths were calculated. ROUNDABOUT CROSSING SIGHT DISTANCE RESULTS Maple Rd and Farmington Rd., Novi, MI East Exit (L & T) East Exit (R) East Entry North Exit (L & T) North Exit (R) South Entry R1 118 - 184 99 - 150 R2 & R4 104 - 104 104 - 104 R3 122 - - 113 - - R5 - 166 - - 105 - Reaction Time (sec) 2 2 2 2 2 2 Crossing Width (ft) 36 36 32 23 23 21 Vehicle Speed (mph) 19 13 13 19 13 13 Gap Acceptance Distance (ft) 336 235 213 235 164 153

NCHRP 3-78b: Final Project Report April 2016 150 Cherrywood and Greenbelt Metro, Greenbelt MD Westt Exit (L & T) West Exit (R) West Entry R1 67 - 150 R2 & R4 40 - 104 R3 97 - - R5 - 86 - Reaction Time (sec) 2 2 2 Crossing Width (ft) 14 14 14 Vehicle Speed (mph) 15 17 17 Gap Acceptance Distance (ft) 133 146 153 Cemetery Rd and Main St., Hilliard OH East Exit (L & T) East Exit (R) East Entry West Exit (L & T) West Exit (R) West Entry R1 142 - 142 150 - 142 R2 & R4 66 - 66 66 - 66 R3 223 - - 99 - - R5 - 110 - - 110 - Reaction Time (sec) 2 2 2 2 2 2 Crossing Width (ft) 22 22 26 24 24 26 Vehicle Speed (mph) 20 20 22 18 20 22 Gap Acceptance Distance (ft) 248 247 309 235 264 309

NCHRP 3-78b: Final Project Report April 2016 151 Nixon Rd and Huron Rd., Ann Arbor, MI East Exit (L & T) East Exit (R) South Entry R1 67 - 130 R2 & R4 43 - 43 R3 74 - - R5 - 87 - Reaction Time (sec) 2 2 2 Crossing Width (ft) 12 12 12 Vehicle Speed (mph) 16 19 22 Gap Acceptance Distance (ft) 125 148 172 E Ellsworth Rd and State Rd., Ann Arbor, MI West Exit (L & T) West Exit (R) West Entry R1 140 - 184 R2 & R4 69 - 104 R3 223 - - R5 - 67 - Reaction Time (sec) 2 2 2 Crossing Width (ft) 25 25 26 Vehicle Speed (mph) 21 17 25 Gap Acceptance Distance (ft) 277 226 341

NCHRP 3-78b: Final Project Report April 2016 152 Old Apex Rd. and W. Chatham St., Cary, NC Westt Exit (L & T) West Exit (R) West Entry R1 61 - 221 R2 & R4 48 - 48 R3 59 - - R5 - 0 - Reaction Time (sec) 2 2 2 Crossing Width (ft) 11 11 13 Vehicle Speed (mph) 16 0 24 Gap Acceptance Distance (ft) 118 0 205 CHANNELIZED TURN LANES CROSSING SIGHT DISTANCE RESULTS Grant Rd. and Oracle Rd., Tuscan AZ Approach SW NE Radius of Curve (ft) 179 176 Reaction Time (sec) 2 2 Crossing Width (ft) 14.5 20 Vehicle Speed (mph) 20 21 Gap Acceptance Distance (ft) 177 237

NCHRP 3-78b: Final Project Report April 2016 153 Sabino Canyon & Tanque Verde Rd., Tuscan, AZ Approach NE Radius of Curve (ft) 176 Reaction Time (sec) 2 Crossing Width (ft) 14 Vehicle Speed (mph) 20 Gap Acceptance Distance (ft) 177 Sabino Canyon Rd. and Cloud Rd., Tuscan, AZ Approach SE Radius of Curve (ft) 89 Reaction Time (sec) 2 Crossing Width (ft) 17.5 Vehicle Speed (mph) 19 Gap Acceptance Distance (ft) 193

NCHRP 3-78b: Final Project Report April 2016 154 E. River Rd. and First Ave. (South Approach) Approach SE Radius of Curve (ft) 67 Reaction Time (sec) 2 Crossing Width (ft) 20 Vehicle Speed (mph) 17 Gap Acceptance Distance (ft) 191

NCHRP 3-78b: Final Project Report April 2016 155 Wilmot Rd. and Speedway Blvd. (North Approach) Approach NW Radius of Curve (ft) 87 Reaction Time (sec) 2 Crossing Width (ft) 20 Vehicle Speed (mph) 19 Gap Acceptance Distance (ft) 210 28th St. and Pearl St., Boulder CO Approach NW NE Radius of Curve (ft) 179 176 Reaction Time (sec) 2 2 Crossing Width (ft) 15 17 Vehicle Speed (mph) 14 20 Gap Acceptance Distance (ft) 129 203

NCHRP 3-78b: Final Project Report April 2016 156 28th St. and Canyon Blvd., Boulder CO Approach SW Radius of Curve (ft) 115 Reaction Time (sec) 2 Crossing Width (ft) 15 Vehicle Speed (mph) 15 Gap Acceptance Distance (ft) 139 Foothills Pkwy. and Arapahoe Ave., Boulder CO Approach SE Radius of Curve (ft) 155 Reaction Time (sec) 2 Crossing Width (ft) 16 Vehicle Speed (mph) 21 Gap Acceptance Distance (ft) 203

NCHRP 3-78b: Final Project Report April 2016 157 Foothills Pkwy. and Baseline Rd., Boulder CO Approach SW NE Radius of Curve (ft) 179 176 Reaction Time (sec) 2 2 Crossing Width (ft) 14 16 Vehicle Speed (mph) 19 19 Gap Acceptance Distance (ft) 171 186 Kenilworth Ave, and E. West Hwy., Greenbelt MD Approach NW Radius of Curve (ft) 96 Reaction Time (sec) 2 Crossing Width (ft) 14 Vehicle Speed (mph) 19 Gap Acceptance Distance (ft) 170

NCHRP 3-78b: Final Project Report April 2016 158 Kildaire Farm Rd. and Tryon Rd., Cary NC Approach SW Radius of Curve (ft) 50 Reaction Time (sec) 2 Crossing Width (ft) 18 Vehicle Speed (mph) 15 Gap Acceptance Distance (ft) 158

Next: 12 APPENDIX E: SITE PHOTO LOGS »
Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities Get This Book
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TRB's National Cooperative Highway Research Program (NCHRP) Web-Only Document 222: Guidelines for the Application of Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities provides guidance to engineers and planners on the design of roundabouts and channelized turn lanes for accessibility. NCHRP Web-Only Document 222 is the final report for NCHRP Research Report 834: Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook.

The accessibility of modern roundabouts and intersections with channelized turn lanes is an important civil rights challenge in the United States that has broad potential implications for engineering practice in this country. This report builds on the results of NCHRP Report 674: Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities. It provides a framework for empirical study and analysis of accessibility performance, documents field testing of several treatments, and provides a research extension through modeling and simulation to expand the results beyond the field-tested sites.

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