Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual (2016) / Chapter Skim
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P A R T 1 Overview The first three sections in Part 1 describe the different levels of planning and preliminary engineering analyses and the potential role of the HCM in supporting these analyses. These sections serve as gateways to the remainder of the Guide: A
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3 A Introduction 1.
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4 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual • The coordinated use of the HCM with simulation models, travel demand forecasting models, mobile source emissions models, multimodal transportation analysis tools, and other planning tools; • The ability to incorporate and test more factors in an analysis than traditional planning tools allow, by integrating HCM methods with existing tools; and • The simplification of calculations to produce a more transparent, quicker evaluation and review process, while not sacrificing the accuracy of the conclusions that are drawn. Similar to the HCM, the Guide describes methods for estimating a variety of multimodal transportation performance measures, including traffic speed, travel time, delay, density, and queues, as well as auto, truck, bus, bicycle, and pedestrian level of service (LOS)
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A. Introduction 5 Once the project moves into final design, it moves out of the realm of planning and preliminary engineering.
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6 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual • Part 2, Medium-Level Analysis Methods, presents guidance on applying and adapting HCM methods for medium-level planning analyses, those planning analyses that focus on a single facility and its component interchanges, intersections, and segments. The sections in Part 2 are organized according to the system elements (e.g., freeway facility, signalized intersection)
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A. Introduction 7 • HCM estimates of performance using a mix of default values and field-measured inputs are usually the next most accurate.
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8 B Medium-Level (Facility-Specific)
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B. Medium-Level (Facility-Specific)
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10 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual The exhibit then lists the Part 4 case studies where the applications of the methods to typical planning analyses are illustrated.
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11 C High-Level Analyses 1.
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12 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual 3. Long- and Short-Range Areawide Transportation Planning Long-range areawide transportation planning, specifically the production of state and regional long-range transportation plans (LRTPs)
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C. High-Level Analyses 13 • Socioeconomic data by traffic analysis zone (e.g., population, employment)
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14 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual • Congestion Reduction, • System Reliability Improvement, • Freight Movement and Economic Vitality, • Environmental Sustainability, and • Reduced Project Delivery Delays. Of these seven goal areas, the HCM can assist agencies in monitoring highway performance relevant to the three goal areas of Congestion Reduction, System Reliability Improvement, and Freight Movement.
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15 D Working with Traffic Demand Data 1.
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16 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual converted into peak hour directional flows. Three factors are used in this process: the K-factor (the proportion of AADT occurring during the analysis hour)
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D. Working with Traffic Demand Data 17 consider sensitivity analyses to address uncertainty in future-year K-factors.
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18 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual rate equivalent to the peak-15-minute volume being sustained for an entire hour. The PHF is calculated as shown in Equation 2, with the peak-15-minute flow rate calculated as shown in Equation 3 (HCM 2016)
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D. Working with Traffic Demand Data 19 6.
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20 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Step 3: Reduce Forecasted Demand within HCM Study Area The forecasted hourly demands for the facilities and segments within the HCM study area that are downstream from the bottleneck should also be reduced. However, the reduction must take into account the traffic entering and exiting the facility within the study area.
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D. Working with Traffic Demand Data 21 Step 4: Caution When Working With Constrained Demands The analyst should recompute the capacity-constrained demands for future scenarios that change one or more capacity constraints (such as adding a lane to a bottleneck)
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22 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual where FFri = future-year forecast volume for turning-movement i (veh/h) , BCi = base-year count for turning-movement i (veh/h)
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D. Working with Traffic Demand Data 23 will reduce the accuracy of one method or the other.
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24 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Step 1: Turning-Movement Matrix Construction. The first step in the process is to construct a turning-movement matrix.
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D. Working with Traffic Demand Data 25 Exhibit 13 shows an example turning-movement matrix after the first step has been completed.
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26 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Should subsequent iterations be necessary, values of Tijf,new created in this step become Tijf,old in the next step. A new matrix of adjusted turning movements Tijf,new and future destination outflows (columns)
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D. Working with Traffic Demand Data 27 Non-Directional Method The non-directional method is intended for general planning purposes where non-directional (i.e., two-way)
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28 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual create its own first-guess proportions from the approach volumes. Once the turning proportions have been specified, the method goes through a series of iterations, similar to the previously described iterative directional method, to develop the turning-movement estimates.
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29 E Predicting Intersection Traffic Control 1.
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30 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual • Apply a factor to the peak hour traffic volume. The specific factor will depend on how peaked the peak hour is.
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E. Predicting Intersection Traffic Control 31 (a)
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32 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual warrants or conditions are desired to be evaluated, then the MUTCD method described in Section E2 should be used instead. As indicated in Exhibit 17, a roundabout is a potential option in many cases, in lieu of stop or traffic signal control.
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33 F Default Values to Reduce Data Needs 1.
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34 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual on default values, such as service volume tables. Similarly, the farther away a final decision is (e.g., identifying potential problem areas for further analysis versus evaluating a set of alternatives versus making specific design decisions)
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F. Default Values to Reduce Data Needs 35 will be applied, during the same time periods that will be used for analysis, typically weekday peak periods.
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36 G Service Volume Tables to Reduce Analysis Effort 1.
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G. Service Volume Tables to Reduce Analysis Effort 37 due to the impracticality of collecting detailed data for so many locations.
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38 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual factor, and free-flow speed are recommended to be compared to local conditions, if possible, when evaluating the suitability of the HCM tables for a particular analysis. For urban streets, through traffic g/C ratio (the percentage of time through traffic receives a green signal at a traffic light)
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G. Service Volume Tables to Reduce Analysis Effort 39 • Pedestrians: percent of facility with a sidewalk (same categories as for bicycles)
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