Chapter 20: Basic principles of intersection signalizationSlide 220.1.1 Components of a Signal CycleSignal timing with a pedestrian signal: ExampleSlide 5Factors affecting the permitted LT movementCFI (Continuous Flow Intersection)DDI (Diverging Diamond Interchange)Slide 9Slide 10Sample problem, p. 46720.2.6 Saturation flow rates from a nationwide survey20.3 The “critical lane” and “time budget” concepts20.3.2 Finding an Appropriate Cycle LengthWebster’s optimal cycle length model20.3.2 Finding an Appropriate Cycle LengthA sample problem, p.47320.4 The Concept of Left-Turn (and Right-Turn) EquivalencySlide 19Left-turn consideration: 2 methods20.5 Delay as an MOE20.5.2 Basic theoretical models of delayThree delay scenariosArrival patterns comparedWebster’s uniform delay model, p480Modeling for random delay, p.481Random delay derivationModeling overflow delayAverage overflow delay between T1 and T220.5.3 Inconsistencies in random and overflow delayComparison of various overflow delay model20.5.5 Sample delay computationsChapter 201Chapter 20: Basic principles of intersection signalizationExplain the meanings of the terms related to signalized intersectionsExplain the relationship among discharge headway, saturation flow, lost times, and capacityExplain the “critical lane” and “time budget” conceptsModel left-turn vehicles in signal timingState the definitions of various delays taking place at signalized intersectionsGraph the relation between delay, waiting time, and queue lengthExplain three delay scenarios (uniform)Explain the components of Webster’s delay model and use it to estimate delayExplain the concept behind the modeling of random and overflow delayKnow inconsistencies existing between stochastic and overflow delay modelsChapter objectives: By the end of this chapter the student will be able to:Chapter 202Four critical aspects of signalized intersection operation discussed in this chapter1. Discharge headways, saturation flow rates, and lost times2. Allocation of time and the critical lane concept3. The concept of left-turn equivalency4. Delay as a measure of service qualityChapter 20320.1.1 Components of a Signal CycleCycle lengthPhaseIntervalChange intervalAll-red interval (clearance interval)ControllerChapter 204Signal timing with a pedestrian signal: ExampleInterval Pine St. Oak St. %Veh. Ped. Veh. Ped.1 G-26 W-20 R-31 DW-31 36.42 FDW-6 10.93 Y-3.5 DW-29 6.44 R-25.5 AR 2.75 G-19 W-8 14.56 FDW-11 20.07 Y-3 DW-5 5.58 R-2 AR 3.6Cycle length = 55 secondsChapter 20520.1.2 Signal operation modes and left-turn treatments & 20.1.3 Left-turn treatmentsOperation modes: Pretimed (fixed) operation Semi-actuated operation Full-actuated operation Master controller, computer control, adaptive traffic control systems for coordinated systemsLeft-turn treatments: Permitted left turns Protected left turns Protected/permitted (compound) or permitted/protected left turnsChapter 206Factors affecting the permitted LT movementLT flow rateOpposing flow rateNumber of opposing lanesWhether LTs flow from an exclusive LT lane or from a shared laneDetails of the signal timingChapter 207CFI (Continuous Flow Intersection)Bangerter Highway & 3500 SouthChapter 208DDI (Diverging Diamond Interchange)Chapter 209Four basic mechanisms for building an analytic model or description of a signalized intersection Discharge headways at a signalized intersection The “critical lane” and “time budget” concepts The effects of LT vehicles Delay and other MOEs (like queue size and the number of stops)Chapter 201020.2 Discharge headways, saturation flow, lost times, and capacity1 2 3 4 5 6 7hVehicles in queueΔ(i)Start-up lost timeSaturation flow rateCapacityCycle lengthEffective greenStartup lost timeClearance lost timeTotal lost timeExtension of greeneGiyiarinhlTilhs11)(3600CgscearyllltaryYtYGgiiiLiiiLiii221Sample problem, p. 467Chapter 2011First approach:Second approach:Eq. 20-620.2.6 Saturation flow rates from a nationwide surveyChapter 2012Chapter 201320.3 The “critical lane” and “time budget” conceptsEach phase has one and only one critical lane (the most intense traffic demand). If you have a 2-phase signal, then you have two critical lanes.34510075450Total loss in one hourTotal effective green in one hourMax. sum of critical traffic demand; this is the total demand that the intersection can handle.N = No. of phases; tL = Lost time in seconds per phase; C = Cycle length, sec; h = saturation headway, sec/vehCNthhTVCNtTCNtLLGcLGLH360036001360036003600Chapter 201420.3.2 Finding an Appropriate Cycle LengthDesirable cycle length, incorporating PHF and the desired level of v/cThe benefit of longer cycle length tapers around 90 to 100 seconds. This is one reason why shorter cycle lengths are better. N = # of phases. Larger N, more lost time, lower Vc.Doesn’t this look like the Webster model?Eq. 20-13Eq. 20-14)/3600)(/(1/36001minhcvPHFVNtChVNtCcLdescLiiiisvratioflowYYLC)/(_155.110Chapter 2015Webster’s optimal cycle length modelC0 = optimal cycle length for minimum delay, secL = Total lost time per cycle, secSum (v/s)i = Sum of v/s ratios for critical lanesDelay is not so sensitive for a certain range of cycle length  This is the reason why we can round up the cycle length to, say, a multiple of 5 seconds. 10155.1iisvLCChapter 201620.3.2 Finding an Appropriate Cycle Length(Review the sample problem on page 473)Marginal gain in Vc decreases as the cycle length increases.Desirable cycle length, CdesCycle length 100% increaseVc 8% increaseFig. 20.4A sample problem, p.473Chapter 2017CNthhTVLGc360036001)/3600)(/(1hcvPHFVNtCcLdesChapter 201820.4 The Concept of Left-Turn (and Right-Turn) EquivalencyIn the same amount of time, the left lane discharges 5 through vehicles and 2 left-turning vehicles, while the right lane discharges 11 through vehicles.0.32511:1125LTLTEandEChapter 2019Left-turn vehicles are affected by opposing vehicles and number of opposing lanes.The LT equivalent increases as the opposing flow increases. For any given opposing flow, however, the equivalent decreases as the number of opposing lanes is increased.51000 1500Chapter 2020Left-turn consideration: 2 methodsGiven conditions: 2-lane approach