Chapter 24. Analysis of Signalized Intersections24.1 IntroductionHCM 2010 Analysis Steps24.1 Conceptual framework for HCM 201024.2.1 The Critical-Lane Group ConceptSlide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 1324.2.5 Effective green times and lost timesSlide 1524.3 The Basic ModelSlide 1724.3.2 Analysis time periods24.3.3 InputSlide 20More discussion on Arrival type:Slide 22Slide 2324.3.5 Estimating the Saturation Flow Rate for Each Lane GroupSlide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 3424.3.6 Determine Lane Group Capacities and v/c RatiosStep 1 and 2 of 24.3.624.3.7 Estimating Delay and Level of ServiceSlide 38Incremental Queue Accumulation (IQA)Incremental Queue Accumulation (IQA) StepsIncremental Queue Accumulation (IQA) StepsIncremental Queue Accumulation (IQA) StepsIncremental Queue Accumulation (IQA) StepsAggregating Delay (p.597)The incremental delay term, d2Upstream Filtering or Metering Adjustment Factor, ISlide 4724.4 A “Simple” Sample Problem21.5 Complexities24.5.1 LT Permitted Left Turns from a shared laneFigure 24.10 Portion of the Green Phase IllustratedSlide 52Modeling permitted left-turns (cont)Slide 54Slide 5524.5.3 Altering Signal Timings Based on v/s RatioModifying signal timing based on v/s ratios (cont)Chapter 24 1Chapter 24. Analysis of Signalized IntersectionsUnderstand the conceptual framework for the HCM 2010 method, including Critical lane group, v/s ratio, saturation flow rate, capacity of a lane group, v/c ratio for lane group, approach and intersection v/c, LOS, and effective green times and lost timeHave general ideas of the modules of the Highway Capacity Manual 2010: Input data, Define movement groups, Compute lane group flow rate, Input or compute phase duration, Compute capacity, and Compute performance measuresWill be able to explain how Arrival Type is determinedKnow how to enter input data into the Highway Capacity Software (HCS2010)Explain the terms of delay models (including Incremental Queue Analysis)Know how to deal with initial queuesUnderstand how the permitted left turns are modeled by the HCM 2010 Understand how the left-turn adjustment factor for compound (protected/permitted) phasing is modeled.Chapter objectives: By the end of this chapter the student will:Chapter 24 224.1 IntroductionWhat’s new in HCM 2010 as compared with HCM 20001. The model has been set up to handle actuated signal analysis directly.2. The estimation of delay is now partially modeled using Incremental Queue Analysis (IQA). IQA allows a more detailed analysis of arriving and departing vehicle distributions.3. The definition of lane groups has been altered. Lane groups are identified and separately analyzed as part of the methodology.“This text focuses on the analysis of pretimed signals because it is more straight forward to present basic modeling theory for fixed time signals.”HCM 2010 Analysis StepsChapter 24 3Chapter 24 4The critical lane group conceptThe v/s ratio as a measure of demandCapacity and saturation flow rate conceptsLevel-of-service (LOS) criteria and conceptsEffective green time and lost-time concepts24.1 Conceptual framework for HCM 2010Five fundamental concepts of the HCM 2010:Chapter 24 524.2.1 The Critical-Lane Group ConceptCritical lane analysis (Section 17.3) vs. Critical lane group analysisCritical lane analysis compares actual flow (v) with the saturation flow rate (s) and capacity (c) in a single lane. Critical lane group analysis compares actual flow (v) with the saturation flow rate (s) and capacity (c) in a group of lanes operating in equilibrium. In either case, the ratio of v to c is the same (when traffic is evenly distributed among the lanes in a lane group). This applies to shared lanes, also.Exclusive right- or left-turn lanes must be separately analyzed because they are separate lane groups.Lane utilization is considered in computing saturation flow rate.Chapter 24 624.2.2 The v/s ratio as a measure of demand & 24.2.3 Capacity and saturation flow rate concepts* The simple method in Chapter 21 (as a comparison – Vc is adjusted by converting into tvu (through vehicle unit) & saturation flow is given):* In the HCM model, demand flow rates are not converted to tvu. It uses veh/hr (though adjusted for PHF). A key part of the HCM 2010 model is a methodology for estimating the saturation flow rate of any lane group based on known prevailing traffic parameters. We may not be able to compare directly lane groups because their conditions are different. So HCM use the flow ratio, v/s, a dimensionless value for comparison purposes. This process is called “normalization.”)/3600)(/(1hcvPHFVNtCcLdesiiifNss0Chapter 24 724.2.3 Capacity (continued) In the simple timing method in Chapter 21, the capacity of the intersection as a whole was considered. HCM 2010 as well as HCM 2000 gives the capacity of each lane group. Demand does not necessarily peak at all approaches at the same time. Capacity may change for each approach during the day. (like the effect of curb side parking, bus blocking, etc.) Capacity is provided to movements to satisfy movement demands. (Note: the critical capacity ratio v/c (for the intersection as a whole) is still calculated in HCM 2010 just like HCM 2000).CNthhTVLGc360036001CgsciiiChapter 24 8The v/c ratio  “degree of saturation”Three issues: (1) Capacity is practically always estimated (because it is difficult to measure.)(2) In existing cases demand is often measured by “departure flows” although it should be “arrival flows.”(3) For future cases, predicted arrival volumes are given (by a planning model) instead of actually counted volumes.Case 1 & 2: v/c > 1.0 resulted in a HCM analysis for an existing signalized intersection. If demand is measured by a departure flow (assuming it was correct), this cannot be accepted because max value v/c = 1.0. If arrival flows are measured, v/c > 1.0 may occur – this becomes obvious because queue forms). Capacity must have been underestimated if queue is not formed despite the fact v/c > 1.0 results. Capacity underestimation is possible because HCM models are national average models.Chapter 24 9Case 3: v/c > 1.0 resulted in an analysis for a planned signalized intersection.In a planning case, both demand and capacity are estimates. But, it may indicate that the forecast demand flow exceeds the