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4. Exploration of Right-Turn-On-Red Models
Pages 43-64

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From page 43...
... In this chapter, the findings from the previous literature are synthesized, and their characteristics are evaluated in light of these objectives. 4.1 Previously Described Models for Right-Turn-on-Red Analysis The literature review identified several models for analyzing RTOR movements for four different basic site configurations: (1)
From page 44...
... Figure 14 shows an intersection diagram indicating several movements at a typical intersection that are likely to influence RTOR: • V1, the conflicting through movement approaching from the left of the subject RTOR movement • V2, the opposing left turn • LT, the shadowed left-turn lane, which is typically considered compatible with RTOR • V3, representing U-turns that might be executed from the shadowed left-turn lane, which are not compatible with RTOR • P1, representing pedestrians crossing the RTOR movement, which are likely to be served concurrently with the green interval for V1 • P2, representing pedestrians adjacent to the RTOR movement. At intersections employing a two-stage crossing with pedestrian overlaps, pedestrian intervals for P2 might be served concurrently with the shadowed left-turn phase.
From page 45...
... This table presents the forms of equations used for either the RTOR volume or RTOR capacity expressions, as well as a listing of which movements are considered in the analysis of each method. The mathematical notation has been adapted from the original formulas (as presented in Chapter 1)
From page 46...
... Movements considered RTOR volume expression RTOR capacity expression V1 V2 LT V3 P1 P2 TRB 2016 qRTOR = 0 , or use field (HCM) measurement None R  Luh and Lu ci = c p  u  f RT 1990 None C    g  ci = S RTOR  CT  Stewart and  C  Hodgson 1995 None S RTOR = 849.82 exp [ −0.00129v ]
From page 47...
... SE Saturation flow rate of receiving (exit) lane SRTOR Saturation flow rate of RTOR movement tc Minimum/critical gap for RTOR movement td Queue clearance time for conflicting through traffic tf Follow-up time for RTOR movement Vc Volume of conflicting traffic As Table 8 shows, a variety of expressions with numerous forms have been used for both volume and capacity adjustments; these tend to rely on similar concepts.
From page 48...
... Many of the models show convergence to a flat-line value early in the analysis, representing the loss of all available RTOR capacity on the left-turn movement; the remaining RTOR capacity is attributable to the through movement at a volume of 250 veh/h/ln.
From page 49...
... Lastly, Figure 17 shows the outcomes for the HCM 2010 model, which considers the shadowed left-turn volume to be a proxy for the RTOR volume. Here, results for the subject right-turn are shown for total right-turn volumes of 500 and 150 veh/h/ln.
From page 50...
... , contains an adjustment that considers the conflicting pedestrian volume P1. This is combined with other potential RTOR intervals for which a weighted average is taken to establish an RTOR saturation flow rate.
From page 51...
... The green time of the shadowed left-turn is also considered. Figure 18 shows an intersection layout that shows various volumes relative to the RTOR movement; the same basic volumes are present as in Figure 14, but there are now two right-turn lanes.
From page 52...
... For shared through and right-turn lanes, this volume (or rather, its proportion of the total volume in the shared lane) constrains the ability for the RTOR maneuver to be executed more strongly than the other volumes, since even a relatively small proportion of through traffic to total lane volume will block the movement for right-turning vehicles.
From page 53...
... V4 V2 V3 V1 RTOR LT P1 P2 Figure 20. Volume and lane configuration used for modeling shared through and right-turn lanes.
From page 54...
... Movements considered RTOR volume expression RTOR capacity expression V1 V2 LT V3 P1 P2 V4 TRB 2016 qRTOR = 0 , or use field (HCM) measurement None Luh and Lu 3600 ci = min ( cc , E )
From page 55...
... Term Explanation cc number of opportunities for RTOR provided by gaps in conflicting traffic ci capacity of the RTOR movement c1 HCM-based approach capacity during green c2 approach capacity when intersecting through and opposing left turns receive an exclusive green c3 approach capacity when shadowed left turns receive an exclusive green E expected number of leading right-turn vehicles in the shared lane k storage length of turn bay (passenger cars) qRT total right-turn flow rate qTh total through flow rate R duration of red for the right-turn movement tc critical headway for right-turn movement tf follow-up time for right-turn movement vi volume of conflicting traffic departing from the rightmost lane vp conflicting pedestrian volume (across the approach; P1)
From page 56...
... The added capacity of the RTOR movement provides a little additional capacity, and thus a slightly lower v/c ratio, when the right-turn volume is a high proportion of the total traffic. However, this disappears quite rapidly.
From page 57...
... As would be expected, the effect is smaller for the shorter storage length (k = 2) , since those lanes are more likely to be blocked as the through volume increases.
From page 58...
... All of the models required basic information about the site characteristics and common parameters reflecting the traffic scenario, which are already included in the existing HCM. Site characteristics include the following: • Lane configuration (number of lanes, shared/exclusive/dual, presence of bicycle lanes, etc.)
From page 59...
... One previous study specified a saturation flow rate for RTOR traffic in particular. This quantity is related to the follow-up time and critical gap for the RTOR movement.
From page 60...
... 2012 Queue clearance time of conflicting traffic 4.3 A Framework for Modeling Right-Turn-on-Red Volume and Capacity The preceding exposition of RTOR volume and capacity models from the literature shows a variety of approaches with a wide range of variation in the outcomes, particularly in the case of an exclusive right-turn lane, which is the most widely studied scenario. Most of the models surveyed in the literature used the entirety of the red duration.
From page 61...
... Depending on the type of modeling approach used, these dynamics may be important or unimportant. Use of statistical modeling with volume inputs may be able to achieve a good estimation of the RTOR volume without the need to dissect the overall red time into its constituent parts.
From page 62...
... If U-turns are permitted from the opposing left-turn lane during this interval, these may also act to reduce the RTOR capacity. • RTOR Interval 3 represents the time when the opposing left turn is served, which is likely to conflict with RTOR vehicles unless there is some reason to anticipate that the two movements would be received by different lanes.
From page 63...
... could be calculated using the right-turn saturation flow s, green time g, number of lanes N, and cycle length C An adjustment is made for a potential reduction in capacity due to conflicts during green due to V2, P2, and V4.
From page 64...
... Chapter 6 presents the models developed for this study, which includes models of RTOR volume using a statistical modeling approach, and models of RTOR capacity including one model based on a synthesis of the literature and another model based on observations from simulation.


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