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From page 56... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-1 CHAPTER 3. MODELING This chapter describes the modeling framework and results for evaluating roundabout corridors in a Highway Capacity Manual (HCM) Read the entire page →
From page 57... ... Evaluating the Performance of Corridors with Roundabouts Page 3-2 Chapter 3 - Modeling Step 10: Determine Automobile Perception Score For the application to roundabout corridors, Step 1 is maintained. The Step 2 procedure for average running time is generally maintained, but certain components of that step, like the free flow speed estimation procedure, are updated for roundabout corridor operations. Read the entire page →
From page 58... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-3 estimate free flow speed in the context of HCM Chapter 17, but is also needed as an input in the geometric delay model described above. Read the entire page →
From page 59... ... Evaluating the Performance of Corridors with Roundabouts Page 3-4 Chapter 3 - Modeling The existence of overlapping RIAs does not constitute a design ﬂaw of the corridor. The studied roundabouts with overlapping RIAs appeared to perform normally. Read the entire page →
From page 60... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-5 flow trip time rate: fu geom SS Ld 11 where dgeom = geometric delay (seconds) ; L = segment length (feet) Read the entire page →
From page 61... ... Evaluating the Performance of Corridors with Roundabouts Page 3-6 Chapter 3 - Modeling intersection i (s/veh) ; Nap= number of influential access point approaches along the segment = Nap,s + p ap,lt N ap,o (points) Read the entire page →
From page 62... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-7 with this model will be a required input for the geometric delay model and the average travel speed model. Read the entire page →
From page 63... ... Evaluating the Performance of Corridors with Roundabouts Page 3-8 Chapter 3 - Modeling PT = passage time seing on signal controller (seconds) ; I = upstream filtering adjustment factor: Xu = weighted v/c ratio for all upstream movements contributing to the volume in the subject movement group; and cA = available capacity (veh/h) Read the entire page →
From page 64... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-9 delays incurred over a segment from increases in volumes may be combined into one empirical model. Exhibit 3-2 shows the updated delay ﬁgure under consideration of control delay and other impediments to vehicles such as midsegment delay. Read the entire page →
From page 65... ... Evaluating the Performance of Corridors with Roundabouts Page 3-10 Chapter 3 - Modeling Data Category Location Input Data Element Basis Traffic characteristics Boundary intersection Demand flow rate Movement group Segment Access point flow rate Movement group Midsegment flow rate Segment Geometric design Boundary intersection Number of lanes Movement group Upstream intersection width Intersection Turn bay length Segment approach Segment Number of through lanes Segment Number of lanes at access points Segment approach Turn bay length at access points Segment approach Segment length Segment Restrictive median length Segment Proportion of segment with curb Segment Number of access point approaches Segment Other Segment Analysis period duration Segment Speed limit Segment Performance measures Boundary intersection Through control delay Through-movement group Through stopped vehicles Through-movement group 2nd- and 3rd-term back-of-queue size Through-movement group Capacity Movement group Segment Midsegment delay Segment Midsegment stops Segment Notes: Movement group = one value for each turn movement with exclusive lanes and one value for the through movement (inclusive of any turn movements in a shared lane) Read the entire page →
From page 66... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-11 Assuming the roundabout analysis segment extends roughly from the midsegment point of the upstream link to the midsegment point of the downstream link, the result is that the HCM Chapter 17 segment is shifted approximately one half block in length from the HCM Chapter 21 segment. For analysis in this research, the team elected to use the lowest common denominator for segment definitions by applying all analysis to a segment equal to half of a link. Read the entire page →
From page 67... ... Evaluating the Performance of Corridors with Roundabouts Page 3-12 Chapter 3 - Modeling Exhibit 3-4: Segment Definitions for Modeling Framework Read the entire page →
From page 68... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-13 3.2.6.2. Variable Definitions Based on the segment definitions above, the following variables were extracted for each upstream and downstream sub segment (Exhibit 3 5) Read the entire page →
From page 69... ... Evaluating the Performance of Corridors with Roundabouts Page 3-14 Chapter 3 - Modeling The exhibit shows the expected portion of the delay incurred while traveling around approximately one third of the circle (distance "x" in the exhibit) at the circulating speed. Read the entire page →
From page 70... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-15 First, the analyst gathers input data and calculates the FFS based on the posted speed limit, segment length, and an assumption that overlapping RIAs are not present. On a portion of a roundabout corridor between two roundabouts, such as Segment B in Exhibit 3 4, the calculation is performed for the downstream sub segment (B1 in Exhibit 3 4) Read the entire page →
From page 71... ... Evaluating the Performance of Corridors with Roundabouts Page 3-16 Chapter 3 - Modeling Note: After Step L, segments can be aggregated to facility level per HCM 2010 Chapter 16. Exhibit 3-7: Computation Process Step A: Gather Input Data: Sub segment length, posted speed limit, ICD, CID, circulating speed, entering flow, roundabout capacity, restrictive median length, curb length. Read the entire page →
From page 72... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-17 Geometric delay, impeded delay, and (optional) average travel speed are calculated separately for upstream and downstream sub segments because the calculations use variables associated with either the upstream or downstream roundabout. Read the entire page →
From page 73... ... Evaluating the Performance of Corridors with Roundabouts Page 3-18 Chapter 3 - Modeling (extending from the yield bar to the downstream midsegment point) Read the entire page →
From page 74... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-19 Variable Name Unit Mean St. Read the entire page →
From page 75... ... Evaluating the Performance of Corridors with Roundabouts Page 3-20 Chapter 3 - Modeling Variable Name Unit Mean St. Read the entire page →
From page 76... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-21 The inscribed circle diameter (ICD) and/or central island diameter (CID) Read the entire page →
From page 77... ... Evaluating the Performance of Corridors with Roundabouts Page 3-22 Chapter 3 - Modeling Exhibit 3-10: Roundabout Influence Area Example (Profiles for SR539 Site Northbound) Read the entire page →
From page 78... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-23 3.3.2.2. Variable Correlations The team investigated the relationships between RIA length and the remaining variables in Exhibit 3 5 by calculating the correlation coefficient (R2) Read the entire page →
From page 79... ... Evaluating the Performance of Corridors with Roundabouts Page 3-24 Chapter 3 - Modeling opposed to 16 to 38 percent) Read the entire page →
From page 80... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-25 models by FFS and circulating speed. The field-observed data for the upstream and downstream RIA are superimposed on the final models. Read the entire page →
From page 81... ... Evaluating the Performance of Corridors with Roundabouts Page 3-26 Chapter 3 - Modeling The model in Exhibit 3-13 shows the same trends as the individual segment models, with increasing RIA with higher FFS and lower circulating speed. The graph illustrates roundabouts on roads with a high FFS that are designed with a low circulating speed can have total RIAs greater than 1,600 feet or about 1/3 of a mile. Read the entire page →
From page 82... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-27 3.3.3.2. Variable Correlations The team investigated the relationships between geometric delay and the remaining variables in Exhibit 3 5 by calculating the correlation coefficient between each pair of variables. Read the entire page →
From page 83... ... Evaluating the Performance of Corridors with Roundabouts Page 3-28 Chapter 3 - Modeling Several of the models indicated geometric delay increases with FFS and number of access points but decreases with the circulating speed. An interaction term between the FFS, circulating speed, and inscribed circle diameter (ICD) Read the entire page →
From page 84... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-29 segment contains a greater portion of travel around the circle (at a reduced speed) Read the entire page →
From page 85... ... Evaluating the Performance of Corridors with Roundabouts Page 3-30 Chapter 3 - Modeling corridor (e.g., segment length, spacing, and midsegment number of lanes) , as well as the geometry of the roundabout itself (e.g., ICD) Read the entire page →
From page 86... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-31 roundabouts, the prevailing FFS is defined as the minimum of the two sub segment FFS estimated for that segment. In other words, the analyst would calculate the downstream FFS for Roundabout 1 and the upstream FFS for Roundabout 2, and apply the smaller of the two numbers as the midsegment FFS for Segment B (see Exhibit 3 4 for numbering and leering conventions) Read the entire page →
From page 87... ... Evaluating the Performance of Corridors with Roundabouts Page 3-32 Chapter 3 - Modeling The simplest models for the upstream and downstream datasets were based on a combination of the segment length and posted speed limit. These models explained 80 to 90 percent of the variability in the data, which is a much beer statistical fit for either the RIA or geometric delay models. Read the entire page →
From page 88... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-33 Note: Assumed Central Island Diameter of 100 ft 3.3.5. AVERAGE TRAVEL SPEED This section describes the development of a model to predict the average speed for the upstream or downstream sub-segment between roundabouts along a roundabout corridor. Read the entire page →
From page 89... ... Evaluating the Performance of Corridors with Roundabouts Page 3-34 Chapter 3 - Modeling segments that were very short and where the free flow speed estimate from the unimpeded routes was similar or somewhat less than the observed speed for other trajectories. Clearly, these negative delays were an aribute of driver behavior during field data collection -- not an adequate reflection of roundabout performance -- and would have introduced inconsistencies and bias in the model estimation. Read the entire page →
From page 90... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-35 Several models for the upstream segment data were developed as a function of the circulating flow, entering flow, posted speed limit, and segment length, which were all significant (p < 0.021) Read the entire page →
From page 91... ... Evaluating the Performance of Corridors with Roundabouts Page 3-36 Chapter 3 - Modeling 3.3.6. IMPEDED DELAY The team's final modeling effort included predicting the impeded delay at each roundabout due to the interaction among vehicles. Read the entire page →
From page 92... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-37 3.3.6.2. Variable Correlations The team performed a correlation analysis similar to the analysis presented in Section 3.3.5.2., but using impeded delay as the dependent variable. Read the entire page →
From page 93... ... Evaluating the Performance of Corridors with Roundabouts Page 3-38 Chapter 3 - Modeling Model Int. Free-Flow Speed (mph) Read the entire page →
From page 94... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-39 3.4. MODEL VALIDATION AND APPLICATION This section presents a model validation and application exercise in two parts. Read the entire page →
From page 95... ... Evaluating the Performance of Corridors with Roundabouts Page 3-40 Chapter 3 - Modeling 3.4.1.2. Roundabout Influence Area The roundabout inﬂuence area (RIA) Read the entire page →
From page 96... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-41 upstream models (R2 = 0.24) Read the entire page →
From page 97... ... Evaluating the Performance of Corridors with Roundabouts Page 3-42 Chapter 3 - Modeling 3.4.1.5. Average Travel Speed As the ﬁnal model, the team predicted the average travel speed on the segment as a function of the FFS and the volume-to-capacity ratio. Read the entire page →
From page 98... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-43 Number Cross Street # Legs Control ICD (ft) 1 Pennsylvania St. Read the entire page →
From page 99... ... Evaluating the Performance of Corridors with Roundabouts Page 3-44 Chapter 3 - Modeling STEP B: DETERMINE FFS FOR SUB-SEGMENT With all data collected, the FFS (Sf) is estimated for each upstream (US) Read the entire page →
From page 100... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-45 Seg # Int. Read the entire page →
From page 101... ... Evaluating the Performance of Corridors with Roundabouts Page 3-46 Chapter 3 - Modeling Seg. Read the entire page →
From page 102... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-47 apN i iapv f xR ddfS Lf L lt 1 other, 1 280,5 600,3 0025.0 0.6 Source: HCM 2010 Equation 17 6 with, (signalized or STOP controlled through movement) (uncontrolled through movement) Read the entire page →
From page 103... ... Evaluating the Performance of Corridors with Roundabouts Page 3-48 Chapter 3 - Modeling Seg. Read the entire page →
From page 104... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-49 STEP J: AGGREGATE PERFORMANCE MEASURES Up to this step, all calculations have been performed on the sub segment level, where upstream and downstream sub segments used different equations to estimate the various performance measures. At this stage, these performance measures need to be aggregated to the HCM 2010 Chapter 17 Urban Street Segments method. Read the entire page →
From page 105... ... Evaluating the Performance of Corridors with Roundabouts Page 3-50 Chapter 3 - Modeling Seg. Read the entire page →
From page 106... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-51 Seg. Read the entire page →
From page 107... ... Evaluating the Performance of Corridors with Roundabouts Page 3-52 Chapter 3 - Modeling Exhibit 3-42: Old Meridian Validation – Summary Results Read the entire page →
From page 108... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-53 The validation results suggest a close match of the predicted FFS for both northbound and southbound, with an error of 0.6 mph and 1.2 mph, respectively. For the average travel speed estimation, the northbound results for the a.m. Read the entire page →
From page 109... ... Evaluating the Performance of Corridors with Roundabouts Page 3-54 Chapter 3 - Modeling Exhibit 3-44: Spring Mill Route Validation – Summary Results Read the entire page →
From page 110... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-55 The Spring Mill corridor validation shows a close match between the model and field estimates. The model slightly overestimated the FFS and the average travel speed by about 2 to 5 mph across the four analyzed routes. Read the entire page →
From page 111... ... Evaluating the Performance of Corridors with Roundabouts Page 3-56 Chapter 3 - Modeling factors (CMFs) for converting signalized intersections and stop controlled intersections into roundabouts. Read the entire page →
From page 112... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-57 Street) were modeled as two way stop controlled intersections. Read the entire page →
From page 113... ... Evaluating the Performance of Corridors with Roundabouts Page 3-58 Chapter 3 - Modeling Corridor Route Route beginning with: 1 and 2 are through routes 3 and 5 are le turns deparng the corridor 4 and 6 are le turns entering the corridor E qu iv al en tS ig na liz ed Ro ut e Tr av el Ti m e (s ) Read the entire page →
From page 114... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-59 Corridor Route Route beginning with: 1 and 2 are through routes 3 and 5 are le turns deparng the corridor 4 and 6 are le turns entering the corridor Eq ui va le nt Si gn al ize d Ro ut e Tr av el Ti m e (s ) Read the entire page →
From page 115... ... Evaluating the Performance of Corridors with Roundabouts Page 3-60 Chapter 3 - Modeling Corridor Route Route beginning with: 1 and 2 are through routes 3 and 5 are le turns deparng the corridor 4 and 6 are le turns entering the corridor E qu iv al en tS ig na liz ed Ro ut e Tr av el Ti m e (s ) Read the entire page →
From page 116... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-61 Anecdotal observations about specific corridors or groups of corridors may explain some of the variability in the results: o Approach delay was lower with roundabouts for all intersections in both major street directions except for SR 539. o Through route travel time (average of both directions) Read the entire page →
From page 117... ... Evaluating the Performance of Corridors with Roundabouts Page 3-62 Chapter 3 - Modeling signalized (or stop controlled) operation. Read the entire page →
From page 118... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-63 unimpeded and free flow travel times along each segment. Again, segments with overlapping RIAs were excluded from the dataset. Read the entire page →
From page 119... ... Evaluating the Performance of Corridors with Roundabouts Page 3-64 Chapter 3 - Modeling should be interpreted along with the volume to capacity ratio term. Like the geometric delay model, a segment with a higher free flow speed is associated with greater impeded delay. Read the entire page →
From page 120... ... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-65 used in the proposed methodology, the direct estimation of average travel speed is a viable model alternative to the HCM 2010 Chapter 17 method, explaining 55 percent and 75 percent of the upstream and downstream variability in average travel speed, respectively. Second, the team presented an external validation of the methodology through application to the Old Meridian Street and Spring Mill Road corridors in Carmel, Indiana. Read the entire page →

From page 56...

... Evaluating the Performance of Corridors with Roundabouts Chapter 3 - Modeling Page 3-1 CHAPTER 3. MODELING This chapter describes the modeling framework and results for evaluating roundabout corridors in a Highway Capacity Manual (HCM)