K ITTE L SON & A SSOC IATE S , INC .TR A NS PO R TATIO N P L A NNING /TR A FFIC E NG INE E R ING

Peter KoonceTRB Annual Meeting

January 9, 2005

Best Practices for Signal OperationsBest Practices for Signal Operations –Lessons Learned from the Portland

Workshop - 2003

Best Practices for Signal OperationsBest Practices for Signal Operations –Lessons Learned from the Portland

Workshop - 2003

Presentation Overview

• Problem Statement• Operational Assessment • Parting Thoughts

Problem Statement:Detection Layout and Location (Design)

• Briefly explain and provide (standard drawings, graphs, or spreadsheets) your detection layout approach.

• Discuss methodology used to determine the number of detectors, what criteria is used?

Problem Statement:Detection Timing (Operations)

• Briefly explain your approach to detector timing

• Discuss the timing functions used – What are the basic parameters that are used for

detection timing and what is their purpose? Volume density functions, Min Green, etc.

Problem Statement:Define Detector Purpose

• Design for Safety and/or Efficiency• Any Consideration of Timing Functions in

Design Phase or vice versa?

Safety Efficiency BothMinimum Green xDetector Switching xVolume-Density Function xDilemma Zone Protection xClearance Intervals Future TopicFuture Topic

Detector Functions and Timing (Operations)

• Considering the following questions– How do different technologies change what you

do?– What effect does speed changes have on your

approach?– Do you change parameters depending on the

operation of the intersection (isolated and coordinated or by time of day)?

– How do additional through lanes (2 or more) effect your approach to timing (gap settings, dilemma zone)?

– How much does the public effect what you do and what effect exists?

– Do you use detector timing features and contrast that with controller timing features?

Problem with the Traditional Approach

• One size fits most!– Signal design phase may

not consider actual operations (or vice versa)

• Session 1 – Design– Consider layout and

placement of detectors

• Session 2 – Timing– Consider operations of the

signal controller

Innovative Notion:

It is an Iterative Process

Are the detection needs different at…..?

• Type of conditions– Urban conditions – Rural conditions – high speed, mostly

uncoordinated/fully actuated

• Time of day– P.M. Peak vs. Middle of night

• Coordinated vs. Uncoordinated• High-speed (>35 mph) conditions• High-speed coordinated

No consensus

No consensus

Practices of Signal Timing – New ITE Report

“The vehicle extension interval is one of the most important actuated controller settings. Here again, diverse techniques are used to select values. The techniques reported include:– field evaluation, – speed and volume, – loop detector location, – Single standard value,– Fixed value, (2, 3, 3.5, and 7 sec were reported),– Length of detection zone,– Time for vehicles to cross intersection (minus 4 s), and– Time required for slow moving vehicle to pass over

loops”

Graphical Representation of Vehicle Control Logic

U n coo rd in a te d O p e ra tion C o ord ina ted O p e ra tion

Vehicle Control Logic

• Two separate cases from a signal control strategy and how it affects detection on a phase

Purpose of Detection in Uncoordinated Operation

M a x im u m G re en

V a riab le G re enP a ssag e G ap

In it ia l In te rva lM in im u m G re en

A ll p ha ses

U n coo rd in a te d O p e ra tion C o ord ina ted O p e ra tion

Vehicle Control Logic

• In high-speed uncoordinated operation, detection settings should not max green (for safety)

• For efficiency, max greens or detection should keep phase time reasonable

Graphical Representation of Vehicle Control Logic

U n coo rd in a te d O p e ra tion

M a x im u m G re en F o rce o ff

V a riab le G re enP a ssag e G ap

In it ia l In te rva lM in im u m G re en

N o n-co ord ina ted ph a se C o ord ina ted P ha se

C o ord ina ted O p e ra tion

Vehicle Control Logic

• Non-coordinated phase or side street ends with: – max green or– Forceoff/split end

** Efficiency under safety

– Safety is maintained if you find a gap

Graphical Representation of Vehicle Control Logic

• Coordinated phase – No dilemma zone possible

without actuated coord phase

** Efficiency over safety?

U n coo rd in a te d O p e ra tion

N o n-co ord ina ted ph a se

Z e ro P o in tY ie ld P o in t

M o n ito r S p e c ia l

D e fau lt P h a seD w e lls in C o o rd P h a se

C o ord ina ted P ha se

C o ord ina ted O p e ra tion

Vehicle Control Logic

Graphical Representation of Vehicle Control Logic

M a x im u m G re en

V a riab le G re enP a ssag e G ap

In it ia l In te rva lM in im u m G re en

A ll p ha ses

U n coo rd in a te d O p e ra tion

M a x im u m G re en F o rce o ff

V a riab le G re enP a ssag e G ap

In it ia l In te rva lM in im u m G re en

N o n-co ord ina ted ph a se

Z e ro P o in tY ie ld P o in t

M o n ito r S p e c ia l

D e fau lt P h a seD w e lls in C o o rd P h a se

C o ord ina ted P ha se

C o ord ina ted O p e ra tion

Vehicle Control Logic

1

2

3 4End Phase

No Dilemma Zone

Suggested Detection PlacementCity of Portland Method

• Graphical method using safe stopping distance to determine appropriate location of detectors

• Identify speed and distance relationship to provide yellow as vehicle reaches the stop bar (approximately 5-10 feet within)

• Largest gap setting is 2.5 seconds to insure efficiency

• Use of presence mode for all detectors

Detection Design and Timing Philosophy

• If vehicle actuates the first advance loop, try to get it through the intersection– Use progressive loops to determine whether

vehicles can stop safely in advance of the intersection

– Use additional loops to minimize gap time

• Display the yellow as vehicle enters the intersection (25 to 40 feet from stop bar at full speed)

City of Portland Detection Placement

0. Front loop standard is 60 feet because safe stopping distance essentially ends at speeds below 15 mph

1. Identify speed of facility and site first detector at safe stopping distance using curve

2. Once vehicle leaves the back loop (back of vehicle), project vehicle path to standard front loop (at 60 feet) using the safe stopping distance speed (25 fps) from front loop

3. Determine carryover by checking what minimum gap setting is at front detector

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Safe Stopping Distance Curve

Detector Location based on SSD - 35 mph casePlace Upstream Detection for Safety

1. Speed in this case is 35 mph, thus place back loop at 183’

2. Vehicle moves from 167’ to next loop at 60’ – would require 4.2 sec at 25 feet per second

(25 fps is SSD from detector at 60’) – use intermediate loop at 1.5 sec from upstream

4.2 sec

Use a third detector to reduce gap setting

Detector Location based on SSD - 35 mph caseDetermine whether additional detectors are needed

2. Split difference between first two detectors Vehicle moves from 167’ to next loop at 115’

– would require 1.5 sec at 36 feet per second– repeat for third loop

Detector Location based on SSD - 35 mph case Additional detector for snappy timing

2. Vehicle moves from 100’ to next loop at 60’ – would require 1.5 sec at 26 feet per second

Gap settings are very low, maintains efficiency

Detector Timing based on SSD - 35 mph case Additional detector for snappy timing

3. Determine carryover by checking what minimum gap setting is at front detector

Vehicle trajectory carries vehicle through intersection at safe stopping distance - 0.5 seconds is minimum gap at front loop, carryover is 1.5 – 0.5 = 1.0 secs

Detector Timing based on SSD - 35 mph case Final Design

Concept of Carryover

• Carryover defines the amount of time a call stays active after the vehicle has left the detector– Portland uses this to reduce the gap time in the

controller and maintain flow rates – In this example, carryover is applied to back

loops Gap Setting + Carryover

1.0 s + 0.5 s = 1.5 s

Gap Setting

0.5 s

Detector locations: 182’, 118’, and 60’Min Gap 0.5 sec, per City standard Carryover from Back loops 1.0 sec

Detector Timing and Design - 35 mph case Final Design

Dilemma Zone Loop Placement(ODOT Method)

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Posted or 85th Percentile Speed

Front Loop Placement

Back Loop Placement

20 MPH N/A 120'25 MPH N/A 140'30 MPH N/A 180'35 MPH 110' 220'40 MPH 160' 320'45 MPH 160' 320'50 MPH 190' 380'55 MPH 225' 450'

In this 35 mph design case with detectors at 220’ and 110’ there are two checks

The SSD is 37 mph from the advance and 24 mph from the front loops

A car leaving from upstream detector travels 110’- (3’ loop + 15’ car length) = 92’ from stop barAt 24 mph or 36 fps, the gap setting is 2.5 seconds

Detector Timing based on DOT method - 35 mph

WSDOT Loop Detection

• Additional loops if gap setting is greater than 3 seconds

Operational Assessment

• A 2.5 second gap compared to a 1.5 second gap– Losing one second every phase, four “phases”

every cycle

• What is the flow rate that will keep a phase operational?– On a 3-lane roadway: See example– On a 5-lane roadway– On a 7-lane roadway

Back to the ODOT 35 mph design case: At 35 mph (51 fps) a vehicle will reach the first detector (nose of vehicle @223’) and travel to over the second detector (@92’) – 131’ at 51 fps = 2.6 seconds + additional gap of 2.5 seconds

Travel Time to Next

Detector

2.6 s

Gap Setting on Detector

2.5 s

Interval between successive vehicles – 5.1 secondsWorst case flow rate: 706 vehicles per hour37% of what is ideal saturation flow rate

Let’s try the PDOT 35 mph design case: At 35 mph (51 fps) a vehicle will reach the first detector (@183’) and travel over the final detector (@42’) – 141’ at 51 fps = 2.7 seconds

Travel Time to Last

Detector

2.7 s

Gap Setting on

Last Detector

0.5 s

Interval between successive vehicles – 3.2 secondsWorst case flow rate: 1,125 vehicles per hour59% of what is ideal saturation flow rate

No Advance Loop Placement

• Proper use of gap timing settings to offer – Efficient performance?– Safety?

• Assume little safety benefit with stop bar detection only

Observations from the Field

• Poor gap setting leads to inefficiencies at the intersections, which suggest higher cycle lengths are needed

• HCM analyses assume saturation flow in all available lanes in theoretical calculations– Does not occur in reality with sloppy gap timing

• Do we need different gap timing under congested conditions?

• Do we need different gap timing to meet different objectives?

Objective Statement for Gap Timing

Conditions

Purpose Settings

Rural Off-peak

High-speed

approaches

Low Volume

SafetyLonger Gaps

UrbanCongest

ed

High Volume

Efficiency &

Safety

Lower Gaps

Advanced

Questions from a Practitioner

• Are safety benefits possible with detector and timing design?

• What is the importance of lane by lane detection?

• Is dilemma zone over multiple lanes a good idea?

• What maintenance issues need to be addressed?

• How do we communicate this to the practitioner?

Research Needs

• Quantify the operational benefits of an additional detector(s) and lower gap settings

• Assess effects on performance under fully actuated conditions (of 5- & 7-lane cross section)

• Quantify the benefits of advance detection settings

• Consider use of a check-out detector at intersection for improving performance