Traffic Signal Timing Diamond Operation
Classic Diamond Interchange Page 2 2
What is a Diamond? Page 3 3
What is a Diamond? (Signal Terms) Two closely spaced signalized intersections of an arterial with a one way pair of frontage roads (Works more efficiently with one controller than two) Arterial Interior Frontage Road Page 4 4
Diamond Interchange Operation Phasing Options 4 Phase 3 Phase Separate Intersection Mode Page 5 5
Phasing Considerations Make it Efficient: run the heaviest movements together Three Phase Allows the main street phases (2+6) or (4+8) Four Phase Allows limited time for the Arterial and opposite side ramp Page 6 6
Phasing Considerations Lane Use Interchange Geometry Width of the Interchange (Internal Storage Capacity) Number of Lanes on The Approach Capacity Entering vs Capacity Inside Volume Distribution Origin Destination Page 7 7
Phasing Considerations Selection of Left Turn Treatment Hardware available Accident history Number of lanes Permissive should not be used with dual left turn lanes. Conflicting Vehicle Speeds Permissive should not be used with approach speeds over 40. Number of Lanes to Cross Permissive should not be used when crossing 3 or more lanes. Page 8 8
Classic Three Phase Arterial Interior Frontage Road Arterial Interior Clearance Frontage Roads Page 9 9
Three Phase Applications Most Effective: Wide Interchanges Provide adequate internal storage Rural Areas with Light Overall Traffic Fewer movements shorter cycle lengths Heavy Through Movements Will be ran simultaneously without having to cross each other Page 10 10
Classic Four Phase Right Arterial Right Frontage Left Arterial Left Frontage Page 11 11
Four Phase Applications Most Effective: Tightly Spaced Interchanges No adequate internal storage Urban Areas More movements longer cycle lengths Heavy Turning Movements Each exterior movement runs independently Page 12 12
Three Phase Examples Wide Intersection Spacing Rural Area (Light Traffic) Page 13 13
Three Phase Examples Wide Intersection Spacing Rural Area (Light Traffic) Page 14 14
Three Phase Examples Freeway not built yet (heavy through traffic) Page 15 15
Four Phase Examples Narrow Urban Diamonds Heavy Turning Traffic Page 16 16
Four Phase Examples Narrow Urban Diamonds Heavy Turning Traffic Page 17 17
Four Phase Examples Narrow Urban Diamonds Heavy Turning Traffic Page 18 18
Four Phase Examples Narrow Urban Diamonds Heavy Turning Traffic Page 19 19
Basic Three Phase Sequence Very efficient under light, even volume distribution. Problem: Does not handle uneven traffic volumes well. Page 20 20
Texas Three Phase Allows shorter, more efficient cycles Flexible Phasing in free and coordination Interior clearance after arterial phases Conditional Service allows backup to re-service interior with frontage road Conditional Service Intervals Page 21 21
Texas Diamond 3 Phase OL K=4+12 OLA=1+2+9+10 6 OLI-1+9+10 2 OLL=5+13+14 OLB=5+6+13+14 OLN=8+16 Page 22 22
Basic Four Phase Sequence Attempts to provides progression for every entering vehicle. Problem: Tends to have long cycle lengths. Page 23 23
Texas Four Phase Adds two travel time (fixed time) phases into 4-phase cycle Increases efficiency Shortens Cycle Lengths Minimizes interior stops by providing internal clearances for every entering movement Travel Time Right Arterial Right Front. Rd Fixed Time Phase Left Arterial Left Front. Rd Travel Time Fixed Time Phase Page 24 24
Classic Four Phase Sequential Phasing Progresses every movement 25% 25% 25 s 25 s 25 s 25% 25 s 25% 100 Second Cycle Page 25 25
Texas Four Phase Same Splits 31 % 25 s 15 s 20% Shorter Cycle 31 % 25 s 15 s 10 s 25 s 31% 15 s 15 s 25 s 31% Wraps around 10 s 80 Second Cycle Page 26 26
Texas Diamond TTI 4 Phase Provides One Stop Operation Always keeps the interior clear Allows fully actuated operation Page 27 27
Texas Diamond Overlap Assignments OL K=4+12 OLA=1+2+9+10 6 OLI-1+9+10 2 OLL=5+13+14 OLB=5+6+13+14 OLN=8+16 Page 28 28
Texas Diamond: 3 Phase - 4 Phase Both use the same load switch assignments Both use the same detector assignments Ring Structures are Different They have a common phase which is used when switching between 3 and 4 phase operation Page 29 29
Ring Structures Texas Three Phase 10 4 2 1 14 8 6 5 Texas Four Phase 2 16 5 4 12 1 6 8 Page 30 30
Diamond Detector Layout Page 31 31
Ramp Detector Placement T = Travel Time for Phase 2 D = Detector Setback = Distance traveled during T+2 Phase 8 D Example: T = 8 seconds Phase 8 approach speed = 40MPH D = (8+2) x (40x1.47) = 588 Travel Time Phase 2 Page 32 32
The Magic of a Diamond Interchange Controller There is none! Pre-programmed controller for standardization Uses standard controller features Same programming rules apply Minimum Green Maximum Green Extension Page 33 33
Modifying a Diamond Pre-Assigned detectors (1 18) are NOT programmable Detectors above #19 are programmable Overlaps are programmable Page 34 34
Customizing Diamond Phasing Overlaps Are Programmable Allow you to customize odd intersections Suggestion: Standard Diamonds Use Default Ring Structure Add/Alter Overlaps Where Needed Suggestion: Unique Applications Sequential Phasing All Overlaps Page 35 35
Problem Heavy Right Turn Driving the Ramp Time Page 36 36
Heavy Right Turn Driving the Ramp Time: How the movements work together Phase 4 and 5 Progressing the SB Movement Phase 12 and 6 Right to Left Travel Time Phase 1 and 6 WB green till gap termination NOTE: After first 8 seconds, no one flows EB Phase 1 and 8 NB Ramp - Right turn finally gets a green Page 37 37
Phasing: Diamond Mode with Additional Overlaps Frontage Road Right Turn Page 38 38
Phasing Modifications Texas Four Phase Available Phase 2 3 16 5 4 12 1 6 7 8 Available Phase 6? 8 Page 39 39
Overlap Assignments with Right Turn Overlap OL K=4+12 OLA=1+2+9+10 OLC=6+7 OLI-1+9+10 2 OLL=5+13+14 OLB=5+6+13+14 OLN=8+16 Phase 7 Page 40 40
Problem Two Way Ramp Needing Left Turn Protection Page 41 41
Phasing : Diamond Mode with Additional Overlaps Exterior Left for 2-Way Frontage Road Page 42 42
Phasing Modifications Texas Four Phase Available Phase 2 3 16 5 4 12 1 6 7 8 Available Phase 6? 8 Page 43 43
Overlap Assignments with Right Turn Overlap OL K=4+12 OLA=1+2+9+10 OLC=6+7 OLI-1+9+10 Phase 7 2 OLL=5+13+14 OLB=5+6+13+14 OLN=8+16 Page 44 44
Problem Closely Spaced Intersection to a Diamond OL K=4+12 2 OLA=1+2+9+10 OLI-1+9+10 OLL=5+13+14 OLB=5+6+13+14 6 OLN=8+16 Page 45 45
Phase Sequence Diagram - Diamond Mode with Adjacent Intersection OL K=4+12 OLA=1+2+9+10 OLI-1+9+10 2 OLL=5+13+14 OLB=5+6+13+14 OLN=8+16 Page 46 46
Overlap Assignments Diamond Mode with Adjacent Intersection 5 2 OL K=4+12 4 2 OLD=4+6+8+16 OLO=6 OLA=1+2+9+10 OLI-1+9+10 6 12 6 OLC=2+8 2 OLL=5+13+14 OLB=5+6+13+14 1 6 OLP=4 OLN=8+16 1 8 2 16 Page 47 47
Split Diamond: Diamond Mode with modified Overlaps Page 48 48
Texas Four Phase Texas Three Phase Right Arterial Right Front. Rd Travel Time Fixed Time Phase Left Arterial Left Front. Rd Travel Time Fixed Time Phase Conditional Service Intervals Page 49 49
Modified Three Phase Diamond Advantages: Runs through movements together Provides progression for left turns Design the Ring Structure A D Ph 2 B Ph 4 D B Ph 5 Ph 7 1 2 4 3 6 5 7 8 Assign the Overlaps A - 1 2 3 B - 5 6 7 C - 1 3 D - 5 7 Ph 4 Ph 8 A Ph 3 C Ph 8 A Ph 1 C Ph 6 B A Ph 2 B Ph 6 Page 50 50
Modified Three Phase: Overlap Assignments 4 OLA OLC 6 2 OLD OLB 8 Page 51 51
Diamond Operation with coordination Coordination rule changes for diamond controllers Dependent on ring structure 10 4 2 1 2 4 12 1 14 8 6 5 16 5 6 8 Still a traffic signal controller Page 52 52
Three Phase Diamond Coordination Phases not serviced in the normal sequence 10 4 2 1 14 8 6 5 Rules: 4=8 1+2=5+6 Cycle Length = 1+2+4 or 5+6+8 Coordinated phase in each ring, on the same side of the barrier (4+8, 2+6, 1+6, 2+5, 1+5) Page 53 53
Four Phase Diamond Coordination Service road time is a combination of two phases 2 4 12 1 16 5 6 8 Rules: 5 must be shorter than 4 and 2 s min time 1 must be shorter than 8 and 6 s min time Cycle Length = 2+4+6+8 Coordinated phase in each ring, on the same side of the barrier (2+5, 4+5, 1+6, 1+8) Page 54 54
Innovative Intersection Designs Based on intersection geometry Goals Reduces the number of phase intervals Reduces cycle length Options Diverging Diamond Displaced Left Turn Diamond Page 55 55
Diverging Diamond Page 56 56
Round Rock Diverging Diamond Field Observation: Made best use of existing bridges The original phase sequence created multiple stops for the left service roads that the city wanted to change Driver routes were not as anticipated Created weaving issue with downstream intersection Page 57 57
Displaced Left Turn Diamond Page 58 58
San Marcos Displaced Left Turn Diamond Field Observation: Took advantage of existing number of lanes under the bridge Internal storage not adequate for the 3 phase operation Single left turn lane was not adequate WB Multiple pedestrian crossing point affected phasing Page 59 59
Hybrid Diamond????? Page 60 60
Questions and Comments www.iteris.com Page 61 61