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From page 11... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 11 2. Research Approach This chapter provides an overview of the following topics: • Review of alternative analysis methodologies • Field data analysis • Service measure evaluation • Simulation tools • Approach for accounting for large truck impacts • Approach for determining follower status 2.1. Read the entire page →
From page 12... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 12 HCM method to more complex situations such as the interaction of climbing and passing lanes and the use of wide shoulders for overtaking purposes, which is a common practice in South Africa. Other important reported limitations involved the significant overestimation of PTSF (which could exceed 100%) Read the entire page →
From page 13... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 13 = ( ) Read the entire page →
From page 14... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 14 Table 2-3. Density thresholds for measuring level of service LOS Density (veh/km) Read the entire page →
From page 15... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 15 presence of heavy vehicles. The v/c ratio is used as an additional service quality measure. Read the entire page →
From page 16... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 16 of the queue. On the other hand, freedom of flow refers to the ratio between the time of undisturbed driving (between platoons) Read the entire page →
From page 17... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 17 The term "faster vehicles" refers to those vehicles that are impeded by slow-moving vehicles and become part of vehicular platoons upon encountering slower vehicles in the traffic stream. The term "desired speed" is used to refer to vehicle speed that is not influenced by the speed of the vehicle traveling ahead. Read the entire page →
From page 18... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 18 performance and lower average speed, and (2) passenger vehicles (autos, SUVs, minivans, and other smaller vehicles) Read the entire page →
From page 19... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 19 model is concave in shape, which is consistent with the shape of the relationship in the German highway capacity handbook (HBS, 2001) Read the entire page →
From page 20... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 20 Probability-Based Follower Identification Catbagan and Nakamura (2010) , building upon previous similar efforts, developed a method that can better estimate whether or not a driver is following or freely moving (Hammontree, 2010) Read the entire page →
From page 21... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 21 where vi = travel speed of vehicle i (km/h) Read the entire page →
From page 22... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 22 2.2.1. Key Traffic Flow Parameter Values/Relationships Base/Free-Flow Speed Despite obtaining data from more than a dozen field sites, the geometric variability and posted speed limits across these sites was quite limited. Read the entire page →
From page 23... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 23 Figure 2-3. Speed-flow data in passing lane of passing lane segment (Oregon site) Read the entire page →
From page 24... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 24 highway. The specific mathematical forms used for both passing lane segments and non-passing lane segments are described in Appendix F Read the entire page →
From page 25... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 25 Again, the specific mathematical form used for this relationship is described in Appendix F Follower Density Follower density is the product of percent followers and density. Read the entire page →
From page 26... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 26 Figure 2-8. Example functional form for follower density-flow data Capacity Of all the field sites, only two experienced flow rates on the order of expected capacity. Read the entire page →
From page 27... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 27 Figure 2-10. High flow site in California (SR-37/Sears Point Rd) Read the entire page →
From page 28... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 28 2.3. Service Measure Evaluation 2.3.1. Read the entire page →
From page 29... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 29 • While almost all highway agencies in the U.S. and Canada use binned vehicle counts as part of their regular data collection programs on two-lane highways, per vehicle data, which is critical in estimating some performance measures on two-lane highways, is only collected by 17% of the responding agencies. Read the entire page →
From page 30... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 30 b. Class II two-lane highways: Highways where motorists do not necessarily expect to travel at high speeds and they include access routes to class I facilities, some scenic and recreational routes, and routes passing through rugged terrain. Read the entire page →
From page 31... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 31 2.3.4. Alternative Performance Measures A number of alternative performance and/or service measures for two-lane highways have been suggested in the literature. Read the entire page →
From page 32... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 32 The researchers argued that average travel speed of passenger cars may more accurately describe speed reduction due to traffic, since passenger car speeds are more affected by high traffic volumes than heavy vehicle speeds. Further, using ATS as a percentage of free-flow speed was viewed as a good indicator of the amount of speed reduction due to traffic and the amount of vehicular interaction in the traffic stream. Read the entire page →
From page 33... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 33 Another measure that has been used extensively both in practical applications as well as in published research is time headway, a major traffic flow microscopic characteristic. For various practical reasons, time headway has been used solely for identifying platoons using empirical traffic data and field measurements. Read the entire page →
From page 34... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 34 of passes achieved is the total number of observed passes for a given two-lane highway, while the number of passes desired is the total number of passes for a two-lane highway with continuous passing lanes with similar vertical and horizontal geometry. Overtaking ratio, along with the average number of passes per vehicle, were also proposed by O.K. Read the entire page →
From page 35... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 35 • On two-lane highways, the prospective performance measure should closely correlate to the platooning phenomenon (and passing opportunities) as well as to traffic level in a logical and meaningful way. Read the entire page →
From page 36... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 36 Table 2-6. Preliminary assessment matrix of performance measures on two-lane highways Performance Measure Type a (1) Read the entire page →
From page 37... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 37 2.3.6. Empirical Analysis of Field Data An empirical analysis based on field data was performed. Read the entire page →
From page 38... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 38 primarily because these programs are based on an outdated software architecture (which limits potential program modifications as well as its ability to run on modern computer operating systems) and/or there is no current developer support for these programs. Read the entire page →
From page 39... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 39 speed. For moderate to steep downgrades, constant brake pressure increases the temperature of the brakes, which can lead to brake fading. Read the entire page →
From page 40... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 40 includes a discussion of the criticisms and limitations of the HCM methodology. The following sub-section presents alternative methodologies that can help address some of the limitations of the HCM methodology. Read the entire page →
From page 41... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 41 = 11 + × ( − 1) Read the entire page →
From page 42... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 42 a similar relationship between heavy vehicle percentage and PCE values for two-lane highways and freeways. PCE values decreased with an increase in heavy vehicle percentage. Read the entire page →
From page 43... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 43 Figure 2-11. Discrepancy between speed-flow patterns for passenger car only and mixed flows Adapted from Exhibit 59, NCFRP Report 31 (Dowling et al., 2014) Read the entire page →
From page 44... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 44 the table. The PCE value(s) Read the entire page →
From page 45... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 45 PCEs in Other Countries Many countries have adopted the HCM as a traffic analysis tool. Unfortunately, these countries cannot always use the same values for adjustment factors (e.g., PCEs, grade, no-passing) Read the entire page →
From page 46... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 46 Table 2-8. HBS Classifications for Vertical Alignment Grade Length (L) Read the entire page →
From page 47... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 47 define levels of service that applied to all subsegment conditions (i.e., all combinations of bendiness class, grade class, and heavy vehicle percentage) for density as compared to ATS. Read the entire page →
From page 48... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 48 Smix = mixed-flow speed (mi/h) FFSmix = mixed-flow FFS (mi/h) Read the entire page →
From page 49... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 49 The flow-related shape parameters (BPmix and Cmix) were based on the shape parameters for the auto-only flow condition (BPao and Cao) Read the entire page →
From page 50... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 50 first, second, and third links were 5280 ft, 3960 ft, and 2640 ft long, respectively. The first and third links had a 0 percent grade with 100 percent no-passing allowed. Read the entire page →
From page 51... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 51 (A) Read the entire page →
From page 52... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 52 Figure 2-15. Flow interpolation issues with scenario 2 in PCE evaluation As shown in Figure 2-15, it was only possible to interpolate the base flow rate for the lowest subject flow rate in scenario 2. Read the entire page →
From page 53... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 53 rate could not be interpolated. Scenario 4 yielded the most PCE values, which can be attributed to the smaller grade used in this scenario. Read the entire page →
From page 54... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 54 Comparison of German HBS and Mixed-Flow Model Methodologies The general idea behind the methodologies in the German HBS and mixed-flow model are the same. Both attempt to capture the interaction between passenger cars and heavy vehicles for a variety of roadway alignment and heavy vehicle percentages using speed-flow relationships. Read the entire page →
From page 55... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 55 due to the alignment. Table 2-12 presents the reductions in FFS used to define the classifications of both horizontal and vertical alignment. Read the entire page →
From page 56... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 56 Table 2-13. Classifications for Horizontal Alignment. Read the entire page →
From page 57... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 57 Table 2-14. Classifications for Vertical Alignment (Downgrades in Parentheses) Read the entire page →
From page 58... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 58 2.6. Approach for Identifying Follower Status The percentage of followers reflects car-following behavior. Read the entire page →
From page 59... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 59 Headway Only Several studies have suggested a headway cut off value between 3 and 4 seconds in identifying vehicles that are in following mode (Van As, 2003; Hoban, 1984; Guell and Virkler, 1988; Pasanen and Salmivaara, 1993; Dijker et al., 1998; Shiomi et al., 2011) Read the entire page →
From page 60... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 60 similar finding has been reported in a few other studies (Al-Kaisy and Karjala, 2010; Lobo et al., 2011; Hoogendoorn, 2005) Read the entire page →
From page 61... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 61 approach the lead vehicle, the speed of the following vehicle and the headway between the two vehicles will continue to decrease until a point is reached when the speeds of the two vehicles will be approximately the same. At this point, the headway between the two vehicles represents what is perceived as the minimum safe headway (hmin) Read the entire page →
From page 62... ... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 62 The research effort to identify the method for identifying vehicles in a following mode is described in Appendix E Summary of Findings This study presents an empirical investigation into the car-following interaction and the estimation of percent followers on rural two-lane highways. Read the entire page →

From page 11...

... NCHRP 17-65 Improved Analysis of Two-Lane Highway Capacity and Operational Performance Final Report 11 2. Research Approach This chapter provides an overview of the following topics: • Review of alternative analysis methodologies • Field data analysis • Service measure evaluation • Simulation tools • Approach for accounting for large truck impacts • Approach for determining follower status 2.1.