Traffic Signal Timing Design Part II

Slide 2 What to do?  Distribute volume among lanes to Identify lane utilization Determine need for lane adjustment Estimate critical lane volumes  Lane volume allocation

Slide 3 Lane Volume Allocation Rules  All turning movements are placed in exclusive left or right turn lanes, if present  Through traffic is distributed evenly among through lanes  Right turns are equivalent to through movements, if no right turn lanes exist  Shared left and through lane requires special procedure

Slide 4 Lane Allocation Example 1

Slide 5 Lane Allocation Example Left turns in exclusive turn lanes

Slide 6 Lane Allocation Example Right turns in exclusive turn lanes

Slide 7 Lane Allocation Example Through in single through only lanes

Slide 8 Lane Allocation Example Through and right in shared lanes WB ( )/2 = 585 SB ( )/2 =

Slide 9 Lane Allocation Example 2

Slide 10 Lane Allocation Example 2 Left & right turns in exclusive turn lanes

Slide 11 Lane Allocation Example Through in through only lanes NB 700/2 =

Slide 12 Lane Allocation Example Through in shared through & right lanes SB ( )/2 =

Slide 13 Lane Allocation Example Shared through & left lanes WB 1. Opposing traffic to LT EB TH+RT = =720

Slide 14 Through Vehicle Equivalents for Left Turns Opposing Volume Through+Right (vph) Through Vehicle Equivalents >

Slide 15 Lane Allocation Example Shared through & left lanes WB 1. Opposing traffic to LT EB TH+RT = = LT =3 TH 3. Total equivalent TH 500+3(75)+100 = Per lane 825/2 = 412.5

Slide 16 Lane Allocation Example Shared through & left lanes EB 1. Opposing traffic to LT WB TH+RT= =

Slide 17 Through Vehicle Equivalents for Left Turns Opposing Volume Through+Right (vph) Through Vehicle Equivalents >

Slide 18 Lane Allocation Example Shared through & left lanes EB 1. Opposing traffic to LT WBTH+RT= = LT =3 TH 3. Total equivalent TH 650+3(120)+70 = Per lane 1080/2 = 540

Slide 19 Lane Allocation Example How many TH in shared lane? EB (120) = 180 vph WB (75) = 187 vph

Slide 20

Slide 21 Phase Plans for Example

Slide 22 Phase Plans for Example 1

Slide 23 Which plan do we use?

Slide 24 Critical Movement  Basic assumption: All movements and approaches have the same saturation flow rate  The lane movement with the highest volume to saturation flow ratio  LT protected The highest lane volume per phase  LT permitted The highest sum of TH or RT single lane and opposing LT

Slide 25 Which Plan to Use? Max {175,250} Max {585,650,180} Max {150,180} Max {500,320,550} Σ CV = =1630

Slide 26 Which plan do we use? Max {( ),( )} Max {( ),( )} Max {650,730)} Max {175,250} Max {585,650,180} Σ CV = =1630 Σ CV = =1565

Slide 27 Which plan do we use?  Maximum critical sum volume for capacity 1400 vph  All phase plans > 1400 vph 2 phase: phase: phase: 1630  Over capacity conditions, need to change lane assignment!

Slide 28 Phase Plans for Example

Slide 29 Phase Plans for Example 2 Note: E-W protected LT is not feasible

Slide 30 Phase Plans for Example 2 Max {( ),(540+75)} Max {( ),( )} Σ CV = =1225 Max {350,450)} Max {533,615} Σ CV = =1245 Max {160,180}

Slide 31 More Phase Plans for Example 2 Overlapping Phases Note: LT are unopposed, i.e. protected More phase plans can be developed

Slide 32 Phase Plans for Example 2 Max {(533),(615)} Σ CV = =1225 Σ CV = =1377 Min {180,160} 20 ( ) Max {350),(450-20)} [ (75)+100]/2=341 Min {180,160} 20 ( ) Max {350),(450-20)} [ (120)+70]/2=426 New LT equivalent

Slide 33 Critical Concepts to Note  Shared LT+TH lanes Use of left turn equivalents for lane volume allocation  LT phase impact on critical lane volumes  Overlapping phasing: exception to the “highest volume is critical” rule  Every intersection is different in terms of which phase plan works best

Slide 34 Left Turn Equivalents? Yes / No Phasing NO effect!!!

Slide 35 Permitted Left Turns? ALWAYS!!! Left turn lane configuration NO effect!