6. signalized Intersections 1 Traffic Management and Control (ENGC - PDF document

Traffic Management and Control (ENGC 6340) Dr. Essam almasri 6. signalized Intersections 1 Traffic Management and Control (ENGC 6340) Dr. Essam almasri References 1. HCM 2000, chapter 16 2. safety.fhwa.dot.gov/intersection/signalized/sig_int_pps051508 /short/sigint_short.ppt 3. mason.gmu.edu/~aflaner/CEIE_360/Signalized%20Intersectio n_ch7_part_1_student.ppt 4. Sarraj, Y. and Almasri , E. 2007, Advanced traffic engineering, lecture notes. Note: - some slides are quoted from given references. - text is from HCM. 2 1

Traffic Management and Control (ENGC 6340) Dr. Essam almasri 4-way Intersection Conflicts 32 conflict points 3 Traffic Management and Control (ENGC 6340) Dr. Essam almasri Objectives of Signal Timing • Minimize delay • Minimize delay • Minimize conflicts • Maximize capacity • Reduce crashes Each objective leads to a different solution We must find an appropriate compromise 4 2

Traffic Management and Control (ENGC 6340) Dr. Essam almasri Warrants for the use of traffic signals A decision on the installation of traffic signals may A decision on the installation of traffic signals may be made on the basis of: � Traffic flow � Pedestrian safety � Accident experience � And the elimination of traffic conflict. 5 Traffic Management and Control (ENGC 6340) Dr. Essam almasri Warrants for the use of traffic signals 3 Quick guide: Quick guide: For traffic flow: Traffic signals are justified if the 2 following traffic flow exists for eight 1 hours on an average day. 4 ≥ 900 vehicles/hour and Flow on the major road (1+2) ≥ 100 vehicles/hour. Flow on the minor road (3) or (4) 6 3

Traffic Management and Control (ENGC 6340) Dr. Essam almasri Warrants for the use of traffic signals For Pedestrian safety: For Pedestrian safety: Signal control offers considerable assistance to pedestrian movements. The Department of Transport in the UK advises that a pedestrian stage is required: 1. if pedestrians across any arm of the junction is ≥ 300 ped./hour ped./hour 2. or if turning traffic flow into any arm has an average headway of < 5 seconds and conflicting with a pedestrian flow of ≥ 50 pedestrian/hour 7 Traffic Management and Control (ENGC 6340) Dr. Essam almasri Signal aspects � The indication given by a signal is known as the signal aspect. g y g g p � The usual sequence of signal aspects or indications in the UK and USA is: In UK In USA • Red • Red • Red/Amber • Green and • Green and • Amber • Amber 8 4

Traffic Management and Control (ENGC 6340) Dr. Essam almasri Meaning of traffic signal indications Color Red Red-Amber Green Amber Signal indication Clear the Stop & Prepare to go intersection keep but do not Go but do not Meaning stopping move cross the stop line 9 Duration (s) 2 3 Traffic Management and Control (ENGC 6340) Dr. Essam almasri Terms Cycle : a complete rotation through all the indications provided. Every legal movement p y g receives a “green” Cycle Length (C) : time (seconds) for the signal to complete one full cycle. Interval: an interval of time during which none of the lights at a signalized intersection changes Change interval: yellow indication for a given ll i di ti f i Ch i t l movement 10 5

Traffic Management and Control (ENGC 6340) Dr. Essam almasri Terms Clearance interval: all red, after yellow Green interval: green indication for a Green interval: green indication for a particular movement Red interval: red indication for a particular movement All-Red: red indication for all approaches Phase: the aspect of a cycle allocated to one the aspect of a cycle allocated to one or more streams of traffic or more streams of traffic 11 Traffic Management and Control (ENGC 6340) Dr. Essam almasri Example : “T” intersection of two one-way streets Cycle : a complete rotation through all the indications g provided. Every legal movement receives a “green” Cycle length: 20 + 3 + 30 sec = 53 sec 12 6

Traffic Management and Control (ENGC 6340) Dr. Essam almasri Terms Permitted Left Turns : a permitted left turn receives a p “green” ball but must yield right of way to opposing movements, used when left turn movements are reasonable and gaps in opposing traffic flow are adequate http://www.drivingschool.ca/drivereducation/page16.html 13 Traffic Management and Control (ENGC 6340) Dr. Essam almasri Terms Protected Left Turns : provided separate phase, left turn movements are protected by arrow, left turns on one-way or T-intersection are considered “protected” within that phase http://www.drivingschool.ca/drivereducation/page16.html 14 7

Traffic Management and Control (ENGC 6340) Dr. Essam almasri Terms Protected/Permitted : left turns are given left turns are given permitted for part of the cycle and then protected for another part of the cycle or protected and then permitted Image source: http://www.fhwa.dot.gov/aard/signals.gif 15 Traffic Management and Control (ENGC 6340) Dr. Essam almasri Types of Signal Timing • Isolated Signals: • Fixed / Pretimed • Fixed / Pretimed Signals which have a designated cycle which does not change regardless of flow or time of day • Semi-actuated Signals in which a major flow sees green unless: a detector on a minor approach is triggered AND a preset, minimum green time is exceeded on the major approach • Fully actuated F ll t t d Signals in which current flow sees green unless: a detector is triggered AND the preset, minimum green time is exceeded on the current approach OR the preset, maximum green time is exceeded 16 8

Traffic Management and Control (ENGC 6340) Dr. Essam almasri Design Process (Webster’s Method) • Collect Traffic Variables: • Hourly volume • Peak hour volumes for all movements • Peak 15-min volumes for all movements • Design • Design 17 Traffic Management and Control (ENGC 6340) Dr. Essam almasri Isolated Intersections • Basic Timing Elements: • Green: Green time Green: Green time • Yellow: Yellow time • Effective Green: Green + Yellow – time vehicles are discharging • All-Red: All movements have red • Intergreen time: Yellow + All-Red • Pedestrian WALK: 4-7 seconds when sign says WALK • Pedestrian crossing time (PCT): time required for a pedestrian to cross the intersection 18 9

Traffic Management and Control (ENGC 6340) Dr. Essam almasri General Approach for Signal Timing (step1) • Select phasing plan Select phasing plan • Calculate design flow rate using peak hour volume and PHF 19 Traffic Management and Control (ENGC 6340) Dr. Essam almasri Peak Hour Factor (PHF) • Design Hourly Volume (DHV): DHV = (Peak-Hour Volume / PHF) Design Hour Volume is the one hour traffic volume used as the basis of design volume used as the basis of design (usually as a prediction of a future condition) 20 10

Traffic Management and Control (ENGC 6340) Dr. Essam almasri Design Hour Volume PHF Adjusts volume to match peak 15 minutes j p PHF = 0.85 Calculated Volume = 1200 v/hr DHV=1,200 vph = 1,411 vph 0.85 21 Traffic Management and Control (ENGC 6340) Dr. Essam almasri General Approach for Signal Timing (Step2) • Find the critical movements or lanes and calculate the critical flow ratios 22 11

Traffic Management and Control (ENGC 6340) Dr. Essam almasri Lane Group • Separates traffic into consecutive movements • Lane group g p – set of movements that has same green phase and move together – Can be one or more lanes • Guidelines for deciding lane groups: – use separate lane groups for exclusive left-turn lane(s) unless a shared left-through also exists for the unless a shared left-through also exists for the approach – use separate lane groups for exclusive right-turn lane(s) unless a shared right-through also exists for the approach 23 Traffic Management and Control (ENGC 6340) Dr. Essam almasri Lane Group 24 12

Traffic Management and Control (ENGC 6340) Dr. Essam almasri Saturation Flow Rate service rate: maximum vehicles that can service rate: maximum vehicles that can be served in 1 hour assuming continuous green and a continuous queue of vehicles • Represents capacity for the lane group • when signal turns green – reaction and h i l t ti d delay time as vehicles start up, then flow becomes uniform – headway becomes uniform 25 Traffic Management and Control (ENGC 6340) Dr. Essam almasri Saturation Flow Rate • sat. flow can be determined directly in the field or calculated • ideal s o = 1,900 pcphgpl (passenger cars per hour of green per lane) cars per hour of green per lane) • adjust s o to reflect non-ideal conditions 26 13

Traffic Management and Control (ENGC 6340) Dr. Essam almasri Saturation Flow Rate Number of vehicles that could enter the intersection after initial startup if constant queue p q existed and constant green s = _3600_(sec/hour) h where: s = saturation flow rate in vehicles per hour of green per lane(vphgpl) green per lane(vphgpl) h = saturation headway (seconds) 27 Traffic Management and Control (ENGC 6340) Dr. Essam almasri 28 14