Intro to Transprtatn Enginrng
Intro to Transprtatn Enginrng TTE 3004C
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Date Created: 10/12/15
TI39E 3004 TRAFFIC CHARACTERISTICS amp TRAFFIC FLOW THEORY Chapter2 Traffic Characteristics III Traffic streams involve I Inherent variability in their characteristics I Range of behavior III Key parameters are used to describe traffic streams and to evaluate analyze and improve traffic plans I Measure of reality I Used to describe and understand traffic streams I Example speed travel time delay etc Types of Facilities III Uninterrupted flow I No external interruptions I No STOP or YIELD signs I No traffic light I Full control of access I Interaction among vehicles with roadway and environment III Interrupted Flow l Incorporate xed external interruptions into their design and operation I STOP or YIELD signs I Traffic signals most common Traffic Flow Characteristics III Parameters traffic flow characteristics that describes the state of traffic stream l Macroscopic III Volume or flow rate III Speed III Density I Microscopic III Speed of individual vehicles III Headway III Spacing Traffic Characteristics Macroscopic Parameters 1 VOLUME OR FLOW RATE 2 SPEED 3 DENSITY 1 Volume and Flow Rate El Traffic Volume number of vehicles passing a point on a highway or a given lane or direction of a highway during a specific interval Expressed at vehicles per unit time per day or per hour Rates of flow q represent flows that exist for periods of time egual or less than hour generally expressed as 1 hour rate I Example III Volume of 200 vehicles observed over 15 minutes period may be expressed as a rate 200 X 4800V hhr Flow Rate q I Example 22 168 vehicles were count over a time interval of 10 minutes What is the flow rate during the 10 minute count and 1 hour 1 68 vehicles 10min 168veh X 60 min min hr 168vehmin 1008 vph Flow Rate III Hourly Volume I Peakhour single hour of the day with highest hourly volume I The peakhour is measured per direction I Both sides of the facility are designed to accommodate the peakdirectional flow during the peak hour III Subhourly Volumes I Quality of traffic flow is related to shortterm fluctuations in traffic demand I A facility may have sufficient capacity to serve the peak hr demand but short term peaks of flow within the hour may exceed capacity and create breakdownqueue Peak Hour Factor III Peak hour factor PHF Min period of time on which traffic conditions are statistically stable Relationship between hourly volume and max rate of flow within the hour Houry Voume Vhourly volume vehicles pHF maxmte offOW Vm15 max 15 min volume Within the hour vehicles pHF V Generally PHF varies between a low of 070 for rural 4Vm15 areas and 098 in dense urban areas Max possible PHF1 this indicate a situation with no variation of flow within the hour I Every 15min period would have a volume exactly one 14 of the full hour Min value PHF025 occurs when the entire hourly volume occurs in a single 15min extreme case of variation within the hour Flow Rate amp PHF n Example 1 HighestV15 500515 500 2000 5004 515530 600 2400 530545 550 2200 545600 510 2040 III Peak Hour Factor PHFhourly volume max hourly flow rate v 2160090 PHF 4 x V15 2400 2 Speed u or S 2 Speed rate of motion in distance per unit time I Speed tells how fast a vehicle is travelling l Speed is inversely related to travel time 5 Sspeed mihr or fts t d distance traversed mi or ft ttime to traverse distance d hr or sec l Speed is collected for III Monitor quality of traffic flow III Monitor speeds III To establish basis for a speed limit I Speed can be measured over a short distance example hundred feet or over a point or over a relative long section example over a mile Speed III Assume speeds of nvehicles are measured on a short distance of d ft or over a point Let u the speed of the vehicle i Let also t be the travel time of that vehicle on that short distance Two ways the speeds can be averaged I Time Mean Speed TMS the arithmetic mean of the individual speeds Average speed of all vehicles passing a point over some specified time period m a point measure Ex radJr dun TM5 Zn1u n i1 2 Speed s or u Space Mean Speed SMS harmonic mean of the individual speeds Average speed of all vehicles moving over a given section of a highway over some specific time period 63 Another way Find total distance n vehicles traveled nd The total time it took for n vehicles to travel is the sum of t Find the ratio of nd over sum of t1 This ratio is SMS nd n 2t il SMS 2 SMS 2 2 Difference between TMS amp SMS 39 Time Mean Speed TMS 39 Average of individual speeds Speed of vehicles passing a point on a highway or lane over some specified time period 39 Space Mean Speed SMS 39 Average speed of all vehicles occupying a given section of highway or lane over a some specified time period Computing the average travel time for a vehicle to traverse the section and using the metrav eltime to compute speed 0 dn Zti Zti i i1 SMS 2 n Example n4 vehicles traveled on a 300 ft section and their travel times and speeds were measured 30 10 40 75 50 6 60 5 Time Mean Speed TMS Space Mean Speed SMS 4 180 t d 4 300 t TMS Zui 45f 5M52 421f n 1 4 5 5 it 285 i1 Find 5 035 20 040 35 045 30 050 15 TVIS amp 5M5 Assume L 20ft Find 5 035 20 200355714 040 35 20o45000 045 30 200454444 050 15 5714 2050 354444 3040 15 4826 TM5Z X X X X 4826ftsec n 100 100 d 20100 SMS 2 120 4762ftsec 20 1 i1 3 Densityk or D III Density number of vehicles occupying a given length of highwayvehicle per mile per lane or vehicle per kilometer Indicates the number of vehicles on a given length of road III Density is often computed from speed and flow rate Measuring density in the field is not as easy as measuring speed of flow flow speed D III Most important parameter because it is the measure most directly related to traffic demand I Measure of the quality of traffic flow I Measure of proximity of other vehicles III influences freedom to maneuver El psychological comfort of drivers Densityk or D III Difference between density and flow rate I Flow rate traffic counts over a period of time a at point III Number of vehicles passing a point over a period of time I Density traffic counts observed over a period of time by limited section of roadwav III Number of vehicles on a roadway section over a period of time III Example If flow rate1800 vph and speed is 60 mph l800vph densit D y 60mph 2 30vpm III Density is difficult to measure typically aerial photos Thus density is easily computed based on occupancy information III Occupancy over a given point can easily be measured by installing devices such as loop detectors on pavement normally magnetic loop detector III Modern detectors can measure occupancy l Occupancy the proportion or percentage of time that detector is occupied or covered by a vehicle by defined time period I Occupancy is measured for a specific detector in a specific lane l Density estimated from occupancy is in units of vehicles per mile per lane I If there are detectors in adjacent lanes the density in each lane may be summed to provide a density in vehiclesmile for a given direction of flow over several lanes Oapp occupancy over a detector 5280 Oapp LV length of average vehicle ft Ld length detectorft LV Ld D density How to find density from occupancy L4H LL Ld r Detecto r Example Detector records an occupancy of 0200 for a 15min analysis period If the average length of the vehicle is 28ft and detector is 3ft long D 0W x 5280 Oappx5280 what is the density 100XL L 0 x5280 D app L 0 o 0 app CCUPanCY 02 02 53280234Jvehmiln O app 0 10 XL Occupancy Average speed 5 HIlh Let t be occupancy for vehicle i time to travel L 00 time occupancy Apparent Occupancy N oapp100Z 39j 1 T N 0 39 go Where Nnumber of vehicles detected in observation time T EXAMPLE For 5 minutes 300 sec time interval and L 20 ft the following time occupancy data was found 42 Ave occupancy time 7 042 sec 100 035 20 040 3 5 Ave speed s 4762ftsec flow 045 30 speed loovthEOmin 5min hour hour 36 96v 39 me D 39 3600 mile sec hour 5280 ft 5280hour N k k k k Oappzloozt100035 20040 35045 30050 1514 300 i1 0W x 5280 014 x 5280 L 20 3696vpmi Traffic Characteristics Microscopic Parameters 1 SPACING 2 HEADWAY 3 SPEED OF INDIVIDUAL VEHICLES Spacing III Spacing Distance between successive vehicles in traffic lane measured from a common point on the vehicles I Front bumper I Front wheels 5280 D 2 d0 where D 2 density vmh da 2 average spacingbetween vehicles in a lane ft Headway III Headway time interval between successive vehicles as they pass a point along the lane measure between common reference points on the vehicles q 3600 ha where q rate of flow vehhlane ha average headway in the lane 5 Headway amp spacing measured bumper to bumper Microscopic parameters III Example If flow rate 1800 vph and speed is 60 mph 1800 vph q denSIt D 30v m y s 60 mph p 2 2 t Spacing 176ft between spacingda5 80wl76ft Egt D 30 vpm 3600 36005 hr headwayha 2560 Headway 2 sec between 7 1800 vehhr consecutive vehicles 17 t speed 2 i if 88 ftsec 60 mph 2 sec Traffic Flow for Continuous Flow El Continuous traffic flow categories I Deterministic Greenshiels Model speeddensity linear model D Density Traffic Flow for Continuous Flow section 23 III Traffic flow models express relationship among elements or parameters l Speed 5 I Flow rate q I Density D Fundamental relationships of traffic flow I FIowSpeed Density qsD where q 2 rate of flow flow rate vehh or vehhlane s 2 space mean speed mih hour mile vehicles miles X vehicles hour D 2 density vehmi or vehmiIane Relationships El Space mean speed and density are measures that refer to as specific section of a lane or highway Flow is a point measure I Stable flow conditionsno queue El Flow rate applies to any point within the section I Unstable flow conditions queue formed El Flow rate represents an average for all points within a section qsD Interrelationships of Fundamentals of Traffic Flow Relationships basic behavioral relationship of uninterrupted flow 0quot R y ir nwr iv Flowspeeddens39ty Dashed line represents 5ffree ow spee j Unstableflow queue that sccritical speed has formed behind Dccritical density breakdown location Djjam density Arriving flow rategt capacity qc capacity qmax 1 areramps on fi eeways 2 Accidents 3 incidents q0 l D0 amp sf 2 Djam density DJ many vehicles and motion stop qgt0 I 3quot V r 1 High speed and low density 5quotquot 1 399 quotM 2 Low speed and high density T11 Interrelationships of Fundamentals of Traffic Flow Relationships basic behavioral relationship of uninterrupted flow umquot 6 will v 753 li taivgh m Flowq0 when N0 Congestion Flowq0 when s0mph free flow speedsf Congestlon xa39 ll39lhfhmi ka a BASIC CONCEPTS OF INTERSECTION SIGNALIZATION HIGHWAY CAPACITY MANUAL 5mm I xv Concepts What is involved in the installation of traffic control signals The decision of installing a traffic light depends on What movements are controlled by traffic signals Critical aspects of traffic lights Concepts Installation if traffic control signals decision depends on Combination of traffic volumes Potential conflicts Overall safety of operation Efficiency of operation Driver convenience Operation of signalized intersections involve 39 Pedestrian movements Vehicular movements Critical aspects Delay as a measure of service quality Discharge headways saturation flow rates and Ios Allocation of time and critical lane concept The concept of left turn equivalency Traffic Signals Purpose assign right of way at intersection streets or highways where without it a continual flow of vehicles on one roadway would cause 1 Excessive delay orand 2 Hazard to vehicles and pedestrians Most misleading aspect regarding traffic control signals is the belief that signals is the safer form of intersection control Bad design Inefficiently placed Improperly operatedpoorly maintained Safer allway stop control Most inefficient type of intersection Determining Need of Traffic Control SignasTCS Engineering Study TCS is justified when all the following conditions are met I One or more traffic warrants are met 1 2 8Hours Vehicle Volume large volumes at intersecting streets For 4hours ofthe day the minor street traffic suffers undue delay trying to entercross the major street Peak Hour the minor street traffic suffers undue delay trying to entercross the major street Pedestrian Volume Pedestrians experience excessive delay in crossings Coordinated Signal System evaluate that the signal can maintain a desired platooning of traffic so that there is coordinated traffic movement along the street Crash experience Evaluate the whether the signal will reduce the frequencyor severity of crashes Roadway Network Consider traffic control signal at the intersection of two major routes I Engineering study its installation will improve overall operation amp safety I Other alternatives have not been effectively or are no feasible Engineering Study4 phases study Phase 1 Vehicle Volumes 9 Fquot5quot39gt quot Vehicle counts hourly turning movements min 12hrs to determine 8 peak hours Peak Hours15 min counts 2hrs amamp pm and sometimes noon Vehicle category classification HV passenger cars motorcycle etc Pedestrians at each crosswalk young kids elderly physical and visual disabilities Observations record erratic and illegal maneuvers and operational problems Area information speed Population of area Accident history collision diagrams past yr accident data etc Phase 2 Traffic signal system 1 2 3 Traffic signal spacing platoon dispersal Projected traffic volume in 5yrs NonNormal business day traffic counts Saturday amp Sunday Example resorts amp water parks Not installed if it would seriously disrupt the signal progression system Should be evaluated to ensure that it can be coordinated with other signals Phase 3 Peak Hour Delay 1 Stopped Time Delay vehicle hours stopped delay on minor streets approaches during 4 hrs consecutive 15min intervals Phase 4 Pedestrian Studies Pedestrian Volumes 1 Pedestrian volumes pedestrian volume count each crosswalk peak pedestrian hour and peak 4hrs 2 Traffic gaps number duration warrant and distribution of gaps same time periods School Crossings same as Pedestrian Volumes Two phase plan N Phase 42 1 West St 1 I I K 1 Right turning movement RT 9 Thru movement Left turning movement LT North St i Right turning movement RT E Thru movement Ar Phase 2 Permitted left turning movement LT Signalized Intersection Operation Signal goes through a sequence of intervals for each signal phase 1 2 3 4 Green 6 Yellow Y Allred ari Red R All red time an Eel Yellow ti eY I I I I I I I I I I I 1 i i 4 Green time GI f REd time R E I I I 39a 1 Change amp Clearance time 7 Cycle C l 39 Phasei Signalized Intersection Operation Concepts 1 Cyclecompete sequence of indications Contains at least 2 phases 2 Cycle length C time that takes to complete one full cycle of indications seconds 3 Interval period of time the indications remains constant no signal indication change Change interval yi llyellow indication for a given moment i Warn approaching traffic of an imminent change in rightof way assignment Transition from green to red Range between 35 25mph and 6s 65mph Predetermined duration Clearance interval arpart oftransition from green to red for a given set of movements iall movements have a red indication Generally1s QI39ISZS Green interval 6 each movement has one green interval during the signal cycle Permitted movements have green indication while all other movements have indication Red interval Ri Each movement has red indication during the signal cycle All movements not permitted have light while those permitted have green light Phase signal phase consists of green interval 6 change amp clearance Yi ari At least 2 phases per plan phase duration GiYi ar Reference quotDetermining Vehicle Signal Change and Clearance Interval lTE informational report 1994 Types of Traffic Signals Pretimed Operation cycle length phase sequence and timing are preset and constant Best suited to intersections where traffic patterns are relatively stable amp predictable Vehicular amp pedestrian volume is relatively equal in all directions Signal spacing is relatively short providing maximum operation efficiency When coordination in signal network is desired Oneway streets with no leftturn phase May have few preset timing patterns Often used in central business district May be used for isolated or coordinated intersections Advantages Can provide degree of speed control by controlling green interval Less expensive to install and maintain Types of Traffic Signals Semiactuated Detectors located at minor streets major streets have priority green most time Cycle length time change andor phase plan might change Nonactuated phase is coordinated with adjacent intersections No recommended for high speed demand approaches or isolated intersections Short green extension on actuated phase provide more efficient operation Actuated Every lane is monitored by detectors Cycle length phase plane amp time change No recommended for high speed demand approaches or isolated intersections Actuated Controller Features Actuated signal controllers are manufactures in accordance of one two standards The most common is NEMA National Electronic Manufacturer s Association and specifies All features Functions Timing intervals Max potential phases 8 phases Max phases activated 4 phases Actuated Controller Features Minimum green time Gmin smallest or min amount of green allocated to each phase at the beginning of the phase Each actuated phase has a min green Unit or vehicle extension U has 3 functions CI Max gap between actuations at a single detector required to retain green CI Amount of time added to the green phase when an additional actuation is received CI It must be of sufficient length to allow a vehicle travel from the detector to the STOP line Cl Recommended extension value 3 sec speed S30mph and 35 5 speed gt30mph Maximum green time Gmax Each phase has a max green time that limits the length of the green phase This starts when there is a quotcallquot or detector actuation on a competing phase Recall switches determine what happens to the signal when there is no demand CI Normally one recall switch is place quotonquot and all other are quotof quot2 when there is no demand the green returns to the phase with its recall switch on El If NO recall switch is place quotonquot the green remains on the phase that had the last quotcallquot CI If all recall switches are quotonquot one phase continues to move to the next at the expiration of the minimum green Yellow and allred intervals Fixed times Actuated Controller Operation l39uiiil Green Period Minimum Cn n Period Extension Pcrind 7 I Unilchhiclu EVlenswn Actuation nn Grucn PillISC 4 Actuation on Competing Phase Aciun 1 ions 25 Vehicle gt 15 Veh arrived on competing phase mum Green Period N Vehicle 39l39imc Figure 203 Operation ol iin Actuated Phase Used with permission ol Institute ofTransportation Engineers mr Humbank 2nd Edition JHK 8 Assouiules Tucson AZ pg 66 Semiactuated Operation I Non actuated A ppnotach39 I No Vehicle arrives onzA ctua39t ed Approach No 7V Call waiting actuated approach No min extension 11V Type of Signal Phasing for Turning Movements Protected Row represents movement without conflict Permitted uses gaps in opposing flow or pedestrians Protectedpluspermitted combination of two Left turn Not opposed Not opposed at any time Opposed LT Not Opposed LT Saturation Headway amp Startup Lost Time Saturation Headway h average headway that can be achieved by a saturated stable moving queue of vehicles Usually this occurs from the 4th or 5th headway position ssaturation flow rate vehhgln hsaturation headway sveh The first 34 headways are larger than quothquot The difference is the additional time drivers takes to react to Green signalG and accelerate Additional time beyond h is A The sum of all A for a given group of movements phase Startup lost time LUstartup los time sphase Aiincremental headway above h seconds for vehiclei 3 Vehicles in an Lnrersecuon Queue Headway secs Measuring headways 1 First headway is the time lapse between the initiation of green and the time front wheels of the first vehicle cross stop line 2 Second headway is time lapse between first vehicle s front wheels cross stop line and time second vehicle s front wheels cross stop line I Only headways of vehicles in queue are considered saturated headways Example Saturation Headway Saturation Flow Rate amp Startup Lost Time HeadwavhS 35 1 35 35035 15 2 66 31 663531 11 3 91 25 05 4 113 22 02 5 133 20 00 6 153 20 00 Saturation headway h20s Time from initiation of green time Lost times Start up last time 1 lost time each time the vehicular flow stops sphase Clearance lost time 2 portion of change interval not used by effective green Time at the end of green Green yar not used by motorists Total lost timetL per phase lost time each time queue starts moving Ee2 Lost time per cycle L time is not used effectively by any movement L is the sum of tL for all critical lanes Time required to discharge queueTn green time needed to move a queue of nvehicles hsaturation headway s nnumber of vehicles in queue Effective Green All red Departure Rate Effective red Effective red Startup Lost Time 1 Extension of Effective Green Clearance IOSt time39 2 Effective Green and Red Effective green For any set or movements there is an amount of time the vehicles are moving at a rate 1 vehicle every h seconds Effective Red For any set or movements there is an amount of time the vehicles are not moving Effective Green 9 All red ari Departure Rate E ective red r E ective red r Startup Lost Time 1 Clearance lost time 2 Extension of Effective Green e LIST OF EQUATIONS Clearance lost time I2 portion of change and clearance interval not used by as effective green Time at the end ofgreen not used by motorists I2yare Effective Green g1 Green time effectively available to a lane group 57 GyartL Lost time for lane group t or phase sum of start up time 1 and clearance lost time 39 t I H 2 I L 1 2 Effective green ratio giC Extension of effective green e portion of changetoclearance interval usable as effective green normally about 2 sec portion of Yellow used by vehicles Effective red ri for a lane group Lost time per cycle L time is not used effectively by any movement L is the sum of t for all critical lanes Signal Timing Examples Fixed Time Plan 1 Fixed Time Plan 2 CD1 9130 5 y13s CD2 9224 5 y24 5 D1 g132 s Y135 D2 g2405 Y23 s all red11 s all red2 2 5 D1 9130 5 y13s D2 r2 92245 y245 r 2 92405 y23s ar225 rGryrarr rGryrarr Cycle Length 1 2 Cycle Length 1 2 K Cycle Length 30 3 24 4 615 Cycle Length 32 3 1 40 3 2 815 Phase Diagrams Example 1 121 LT 122 E W T D3 5N T c121 g1105 Y13s 122 g2255 Y23 1 3 93205 Y34 Phase Diagram r3 93205 y34s i Gi Vi ari Cycle Length l 2 3 Cycle Length 10 3 25 3 20 4 65s Capacity Lane or Lane Group If the light is GREEN all the time the saturation flow rate represents the capacity of an intersection The portion of real time that is effective green Effective green timeCycle engthportion of the cycle used by motorists c capacity of lane or lane group i vehh ssaturation flow rate for lane or lane group i vehhg g effective green time for lane or lane group i s Ccyce length 5 339quot 39 mquot l quotI12 Book Example 1 Given 1 phase C60 s G27 s Yyar 35 Saturation headway h24 sveh Startup lost l12 5 Clearance lost time l2ls What is the capacity of this movement per lane Method 1 Time in 1 hr 3600 s No Cycles in hr 36006060 Red Time in hr CGY60 cycles RedR 60273601 800 5 Lost time in hr tL1l260 cycles Lost time per phase in hr 605 tLI360180 s Remaining time in hr is the green time gi used by movements 1hr red timetotal lost time c360018001801620 5 Then capacity of lane csh1 620246 75 vehhgln Book Example 1 Given 1 phase C60 s G27 s Yyar3 Saturation headway h24 sveh Startup lost 12 5 Clearance lost time 2ls What is the capacity of this movement per lane Method 2 s 3600 h s 3600241500 vehhgln 9i Gi 39 tL g 273327 5 Then capacity of lane cisx g i 1500gtlt a CV 60 ci 675vehhIn Critical Lane Concept Since demand is not evenly distributed among lanes one lane has the most intense traffic The signal must accommodate traffic in the lane with most intense traffic high volume per phase The lane with the highest volume is the quotCRITICAL LANEquot The total flow in critical lanes is the sum of all criticallane flows If the signal accommodate the total critical lane flows then all other lanes will be accommodated as well Illustration 1 Critical Lane Concept Given Two phase plan W E 600pchln E W 200 pChIn 6W 200pchln SN 800 pc N S 300 pchln pcpassenger car units West St E L 0 CL O O 00 Determine the critical lane per phase What is the flow in each critical lanes What is the total flow in critical lanes Illustration 2 Critical Lane Concept Given Two phase plan W E 600pchIn E W 200 pChIn 6W 200pchln S N 800 pchIn S N RT 900 pchIn I N S 300 pchIn West St 900 pchln l5 L 0 CL O O 00 Determine the critical lane per phase What is the flow in each critical lanes What is the total flow in critical lanes More About Critical Lane Concept Rules 1 There is one critical lane and criticallane flow for each discrete phase NO overlapping phases 2 Except for lost times there must be one critical lane moving during every second of effective green time in the signal cycle 3 Where there are overlapping phases the potential combination of lane flows yielding the highest sum of critical lane flows while preserving the requirement above identifies the critical lanes Capacity Using CriticalLane Volumes Each signal phase has one critical lane Except for lost times one critical lane is always moving Each phase has lost times tL Another way to determine capacity The max sum of critical lane volumes Vccan be determined as Capacity Using CriticalLane Volumes The lost time per cycle assume the lost time is constant for all phases The effective green time in 1 hr 7F Capacity Using CriticalLane Volumes Single intersection approach Max sum of critical lane Equations from previous slide VOlumeS 0 Lost time 1 hr Lost time per cycle Converting into volume effective green in an hour Effecting green within saturation headway 1 hour TG Book Example 3 Given 2 phases SOIUtioni 39 C50 5 Max sum of critical lane flows Total lost time L4 sphase Saturation headway h24 sveh What is Max sum of critical lane flows During 3120 sec of effective green there is one vehicle moving every 24 sec H Critical vc Ratio XC Critical vc ratio X for the whole intersection V Xc lt 1 signal timing and intersection geometry are adequate Xc gt 1 signal timing and intersection geometry are NOT adequate Xc depends on CCL CCL is minimum when Ctakes max acceptable value Illustration 3 Xc ratio for WHOLE Intersection Given Two phase plan North St 800 pchln No lost time assumed WestSt Cycle length 605 GM Critical lane flow WE 600pchln Critical lane flow SN 800 pchln Saturation flow rate2000pchn Solution Riki f 5 ifer ram w 2 2mm O o Sum o Cl lllclllrl mc VulnmmJ Cyclu ungm C Figure 173 Muximum Sum I39CrillcaILzmc Volumes Pluucd Relationship between N C and VC 1 Capacity increaseswith C Longer C fewer cycles in 1 hr Fewer phases less lost time in 1 hr Less lost time more effective green time Note Increasing C may result in small increases in capacity More About Capacity Capacity decreases as number of phases increases more lost times Shorter cycle lengths yield less delay Shorter cycle lengths yield vc ratio among 080095 When the cycle length is significantly long there will be situations when vehicles on one approach are waiting for a green while there is no demand in the conflicting approaches Fundamentals of Signal Timing Simplest signal plan 2 phases Phase diagram shows all movements being made in a same phase Ring diagram shows which movements are controlled by which quotringquot on a signal controller Ringcontrols one set of signal faces Opposite movements are controlled by separated rings Phase diagram 39Phase A A 1 cycle 39Phase B B with 2 phases 1 lnlcrsrciiml Lnynul lmclushc LIVR39I lams Pllnllllll Cycle Length C v 4 4 gt c Ring Dngrum RIB Illustration ol u TwoPhase Signal Ring diagram Description amp Illustration of Phase and Ring Diagrams u lmursucliun Luyum exclusive L39I39R39l39 lanes uplluna l cycle Length 1 cl km 183 llluslralion of u TwoPhase Signal Ring diagram Phase diagram Representation of Phase amp Ring Diagrams PhaseA A amp Phase Ema Ringl Ringz I g 1 K x 4m 239 E 1 3 an x u c Ring Diagram 183 lliisiraiion ofuTwothise Signal Ring diagram Cycie iengm Ci Leading amp Lagging Green Phase Leading and lagging green phases signal plans with different phases for the opposed LT Opposed LT are protected and have different green time Components 1 Leading green The LTmovements in the direction of green is protected Vehicles in one direction get green while vehicles in the opposite direction are stopped 2 The overlapping through green LT vehicles in the initial green direction are stopped while though and RT vehicles are released LT can be allowed as permitted LT in both directions This called compound phase 3 The lagging green vehicles in initial direction all movements are stopped The opposed direction have green and the LT are protected EW Leading and Lagging u lnmseclmn Layum No transitions Continuous movement Ringl ngz 7 tbAl g f W m Overlapping 4quot C g A m hA Overlapping if 7 r3 le bB Figure 35 Leading and Lagging Green Illustrated 1c ng Diagram No transitions Continuous movement quotsubphase ILU abB a Inlurscciinn Lxumli ng Ring A5 41 G Ic Ring 16 Exclusch Len Turn Phase Plua Leading Green Phase Illustrated Splitting the Green The effective green in the cycle is divided among various signal phases in the cycle Total effective time for phase i Critical Lane Volume Example 1 3 discrete phases3 phase transition in cycle Non Overlapping CI Each phase has one Critical Lane lCLl Volume CI In each phase the Critical Lane Volume is the one with the highest vs or v 3 discrete phase and 1 critical lane volume per phases CL vs are 3 vs020 x vs035 x vs045 Total sum of CL02003504510 Overlapping CI EW need to find CRITICAL PATH thru the signal cycle CI NS need to fine critical lane group NO OVERLAP l l w Note same vs because it is a continuous movement Finding Critical Path for EW phases El All phase on amp phase on movement combinations rule one critical movement per phase for overlapping phases only l5quotllwglt IQMV E EBL WBT 39 0K one CL movement per phase X EBL EBT N0 Violate rule of one CL per phase x EBT WBT a NO Violate rule of one CL per phase B EBT EBT aa OK one CL movement per phase Summary only two possible paths ELB WBT and EBT EBT Sum of vs for possible combinations 1 EBL WBT 394 sum of vs o27o3oo57 2 EBT EBT sum of vs 021 because it is a continuous movement Then the there is one critical path and one critical lane group El EW Critical path 39 4 CINS Critical lane group Then you need to provide enough green for AI VS057 Vs028 sum all vs WBTEBL NB 0570Z8 085 Next 2 slides explain how to select CRITICAL PATH in previous EXAMPLE Remember Rule 1 One critical movement per phase Critical movements in a critical path ONLY for overlapping phases CAN T be equivalent to a given PHASE Overlapping CI EW need to find CRITICAL PATH thru the signal cycle CI NS need to fine critical lane group NO OVERLAP Note same vs because it is a continuous movement Finding Critical Path for EW phases CI All phase A1 amp phase A2 movement combinations El Rule one critical movement per phasetwo critical movement combination in a critical path CAN T be together in one phase Critical movements have to be in different phases x EBT WBT d equivalent to Overlapping CI EW need to find CRITICAL PATH thru the signal cycle CI NS need to fine critical lane grop NO OVERLAP Note same vs because it is a continuous movement Finding Critical Path for EW phases El All phase A1 amp phase A2movement combinations rule one critical movement per phase for overlapping phases only i A quot El EBL WBT 39 NOT Equivalent to Example 2 Same vs because it is a continuous movement Same vs because it is a continuous movement Finding Critical Path 8 combinations 3 discrete phases plan B Exxxxxx EBL WBT WBT AI OK Same movement but in different phases EBL WBT EBT a a NO 2 movement in same phase EBL WBL WBT H F 1 NO 2 movement in same phase EBL WBLEBT A F NO 2 movement in same phase WBL WBTWBT NO 2 movement in same phase WBLWBTEBT I a NO 2 movement in same phase WBLWBLWBT F a N0 2 movement in same phase WBLWBLEBT F F OK Same movement but in different phases Two possible paths 1 EBL WBT WBT 39 lt 4 Sum vs 018022040 2 WBLWBLEBT Q gt Sum vs 017 030 Critical Path Same vs because it is a continuous movement Same vs because it is a continuous movement sum of all vs 047025072 LOS C or D 393 discrete phases plan Example 3 Find Critical Paths Leading amp Lagging Options 1 Leading green without lagging green or vice versa Tintersections One way street 2 Compound phase allowing permitted LT in phase AZ This a protectedpluspermitted phase 3 Leading andor lagging can be added to the crossing direction Cycle Length amp Phase Plan Cycle length Thumb Rule 55150 seconds90 seconds GOOD GUESS CI 45 55 150 180 l39l CI Good guess when N0 information is available If traffic is low use C lt 905econds If traffic is high use C2 90 seconds Phase Plan No information available Start with 2 phases plan minimum number of phases Green Time use the quot22 rulequot CI For every car give 2 seconds sat headway headway amp 12 gt 22ncars CI Example if n5 then Green time22512 sec of green CIStarting Point CphasesG90 2 2 2 90 sec 2 phasesgz sec per car Start up lost time Improving guess Improving Cycle Length starting guess El Demand is low use shorter cycle length El Demand is high use longer cycle length Cl Example CI Xc060 This indicates LOW demand then good guess are C 60 or 50 5 CI Xc095 This indicates HIGH demand then good guess is to start with 905 and up Improving Phase Plan Add LT phase If you have many accidents crash F Add LT phase Saturation Flow Rate A base saturation flow rate is modified by a series of multiplicative adiustment factors to determine the total saturation flow rate for each lane group under prevailing demand conditions s Where ssaturation flow rate for lane group vehh sobase saturation flow rate pchgln 1900 pchgln unless field data has been used to establish a locally calibrated value N number of lanes in the lane group fadjustment factor for prevailing condition i wane with interference a area type Lpb pedestrianbicycle LU lane use with left turns TRright turn LTeft turn prpedestrianbicycle interference with right turns HVheavy vehicles ggrade pparking bblocal bus blockage 1 Adjustment for Lane width Standard lane with12ft No lane width narrower than 9ft should be analyzed Lane widths less than 10ft are not recommended WAverage lane width for the lane group ft 2 Adjustment for Heavy Vehicles HVany vehicles with more than 4 wheels touching the ground during normal operations if 1 51 I39 PHVproportion of heavy vehicles in the lane group demand flow EHVpassenger car equivalent for a heavy vehicle For signalized intersections EHV2 HV are RV Trucks and NOT stopping buses 3 Adjustment for Grade CI CI Downgrades have negative percentage and fggt1 Upgrades have positive percentage and fglt1 Ggrade 4 Adjustment for Local Bus Blockage CI Accounts for the impact of local buses stopping to pick up and or discharge passengers at nearside or far side bus stop within 250ft ofthe near or far STOP line The primary impact is on the lane in which the bus stops It assumes that each bus blocks the lane for 1445 of green Adjustment factor applied to lane blocked 5 Adjustment for Parking Conditions Involves CI Parking conditions and movements CI Number of lanes in the lane group CI If there is NO parking adjacent to the lane group fp1 CI If there is parking adjacent to the lane group the impact in the lane adjacent to the parking is a 10 loss of capacity plus 185 of blockage for each movement into or out of a parking space within 250ft of the STOP line The impact on adjacent lane 18 3600 P adjustment factor applied only to the lane adjacent to the parking lane P 090 Nmnumber of parking movements per hour into and out of parking spaces within 250ft of the STOP line mvtsh Assuming other lanes are unaffected F 131 EUVJP if Ezeee g 787 NNumber of lanes in the lane group Combining previous equations Os Nm 180 if Nmgt180 use 180mvtsh fpmin005 fpn0 parking10 6 Adjustment for Type of Area CI CBDCentral business Districtzfa090 CI Other location fa100 7 Adjustment for Lane Utilization CI Accounts for unequal use of lanes by approaching demand flow in a multiple lane group f Vg g1 Vgdemand flow rate for the lane group vehh Vg1demand flow rate for the single lane with the highest volume vehhln N number of lanes in the lane group 7 Adjustment for Right Turns RT vehicle has a saturation flow rate that is 15 less than Through movements El Exclusive RT lanes fm085 CI Shared lanes fRT1015PRT CI Single lane approach fRT10135PRT PR7 proportion of rightturning vehicles in the lane group 8 Adjustment for Pedestrian and Bicycle Interference with Turning Vehicles beP139PRT139Apr139PRTA beP139PLT139Apr139PLTA PRT proportion of right turns in the lane group PLT proportion of left turns in the lane group Apr pedbicycle adjustment for the permitted portion of the phase PTRA proportion of right turn green time in a protected phase PLRA proportion of left turn green time in a protected phase 9 Adjustment for Left Turns 1 f 1 00513 PLT proportion of left turns in the lane group Problem 1 One way sharedlane intersection approach has the following characteristics 605 effective green time in a 1005 cycle Four 11 ft lane 10 HV Parking on the side and 15mvtsh within 250ft og stop line 20 local busesh stopping at a nearside bus stop 8 RV 12 Left turns No bicycle traffic CBD location No opposing approach No pedestrians on sidewalk 6 grade Estimate the saturation flow rate and the capacity of this approach Solution Capacity cs gC Saturation flow rate r 3 6 W7 fn r I 37 P x0 A 0 zmi i 2 LLQTLQETQ Q 501900 pchgln N4 lanes Adjustment for location For CBD fa090 Adjustment for grade Solution Adjustment for H V A 0 m 73 1 11 7 JQ Jg 7 Solution Adjustment for bus blockage Adjustment for lane utilization pedestrianbicycle interference fLU1 prb 1 andepb1 Solution Saturation flow rate quot 533 39
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