Slide 1Key Steps of signal timing development, p.48921.1 Development of signal phase plansLT treatment (continue), p.490LT treatment (continue), p.491LT treatment (continue), p.491Slide 7Fig 21.2 Selected signal phase arrows illustrated21.1.3 Phase and ring diagrams (continued)21.1.4 Common phase plans and their useWith a protected left-turn phaseExclusive LT phase with leading green phaseEight-phase actuated control (NEMA), p.497Lead vs Lag (with Protected/permitted)Yellow TrappingProtected-permitted left-turns (1)Protected-permitted left-turns with parallel through trafficSlide 18Lag-left turn with no opposing left turnLag-left turns moving simultaneouslyThe exclusive pedestrian phaseT-intersection & 5-leg intersectionRight-turn phasing and RT lane21.2 Determining vehicular signal requirementsSlide 25Eliminating the dilemma zoneSlide 27Slide 28Slide 2921.2.2 Determining lost timesSlide 31Slide 32Slide 33Slide 3421.2.4 Determining the desired cycle length21.2.5 Splitting the greenSlide 3721.3 Determining pedestrian signal requirementsSlide 39Slide 4021.4 Compound signal timing21.5 Simple signal timing applicationsChapter 21 1Chapter 21: Fundamentals of Signal Timing and Design: Pretimed SignalsExplain the basics of signal timingKnow how to handle left-turn vehicles by various phase plansDefine terms related to phasingExplain how change and clearance intervals are determinedExplain how pedestrians are dealt with in signal timingState a few more ways to deal with left turnsGet familiar with typical steps for simple signal timingChapter objectives: By the end of this chapter the student will be able to:Chapter 21 2Key Steps of signal timing development, p.4891. Development of a phase plan and sequence2. Determination of vehicular signal needs:(a) Timing of change interval (y) and clearance interval (ar)(b) Determination of critical lane volume (Vc)(c) Determination of lost time per phase (tL) and per cycle (L)(d) Determination of desired cycle length (C)(e) Allocation of effective green time3. Determination of pedestrian signal needs: (a) Determine min. pedestrian green(b) Check if vehicular greens meet min pedestrian needs(c) Check the need for pedestrian actuators or for adjusting timingThe process is not exact, nor is there often a single “right” design and timing for a traffic signal.Chapter 21 321.1 Development of signal phase plans21.1.1 Treatment of left turns (the single most important feature that drives the development of a phase plan)Two general guidelines (not absolute criteria):• vLT ≥ 200 veh/h, or• vLT*(vo/No) ≥ 50,000 (Cross product rule)2 left turn vehicles/cycle may be able to turn left as “sneakers” during the yellow interval (about 120 LTs per hour).The most critical aspect of signal design and timing is the development of an appropriate phase plan.vLTvo/NoChapter 21 4LT treatment (continue), p.490Permitted LT phasing should be provided when the following conditions exist:1. The LT demand flow within the peak hour falls within the “permitted” portion of the figure below. 2. The sight distance for LT vehicles not restricted. 3. Fewer than 8 LT accidents have occurred within the last 3 years at any one approach with permitted-only phasing. (Permitted LT phase must exist to apply this criterion.)Figure 21.1Chapter 21 5LT treatment (continue), p.491Fully protected phasing is recommended when any TWO of the following criteria are met:1. LT flow rate is greater than 320 veh/h2. Opposing flow rate is greater than 1,100 veh/h3. Opposing speed limit is greater than or equal to 45 mph4. There are two or more LT lanes (in this case, only protected LT phase is used.)Chapter 21 6LT treatment (continue), p.491Fully protected phasing is also recommended when any ONE of the following criteria are met:1. There are 3 opposing lanes, and the opposing speed is 45 mph or greater2. LT flow rate is greater than 320 veh/h, and the percent of heavy vehicles exceeds 2.5%3. The opposing flow rate exceeds 1,100 veh/h, and the percent of LT exceeds 2.5%4. Seven or more LT accidents have occurred within 3 years under compound phasing. 5. The average stopped delay to LT traffic is acceptable for fully protected phasing, and the engineer judges that additional LT accidents would occur under the compound phasing option. Compound phasing (protected-permitted) may be considered when LT protection is needed but none of these criteria are met. – Use compound phasing at less critical areas because it is a confusing phasing.Chapter 21 7 Phasing can be used to minimize conflicting movements and associated hazards. But the higher number of phases means decreased efficiency and increased delay.  Each phase add about 3 to 4 seconds of effective red (lost time). The more phases you have more delay you create. But, saturation flow rate increases because of less conflicts. Hence, look for balance between them.  The LT saturation flow rate is at the mercy of on-coming vehicles for permitted left turns. A phase plan must be implemented in accordance with the standards and criteria of the MUTCD, and must be accompanied by the necessary signs, markings, and signal hardware needed to identify appropriate lane usage.  See MUTCD about signal heads, associated signs, etc. The phase plan must be consistent with the intersection geometry, lane use assignments, volumes and speeds, and pedestrian crossing requirements.  e.g. If there is no LT-bay or exclusive LT-lane, do not provide a protected LT phase. It’s useless!21.1.2 General considerations in signal phasingChapter 21 8Fig 21.2 Selected signal phase arrows illustrated21.1.3 Phase and ring diagramsChapter 21 921.1.3 Phase and ring diagrams (continued)Phase diagram: Shows all movements being made in a given phase within a single block of the diagram.Ring diagram: Shows which movements are controlled by which “ring” on a signal controller.A “ring” of a controller generally controls one set of signal faces. Thus, while a phase involving two opposing through movements would be shown in one block of a phase diagram, each movement would be separately shown in a ring diagram.Chapter 21 1021.1.4 Common phase plans and their useThis works for either case of having a left-turn bay or not having a left-turn bay. If a left-turn bay is available, performance and safety increases.Basic two-phase signalizationChapter 21 11With a protected left-turn phaseGeneral guidelines to deal with left-turn