TRBTRAFFIC SIGNAL SYSTEMS COMMITTEE

MIDYEAR MEETINGJULY 25-27, 2003 – TORONTO, ONTARIO

DENNIS EYLERVICE PRESIDENT

SRF CONSULTING GROUP, INC..MINNEAPOLIS, MN

TRAFFIC RESPONSIVE TRAFFIC RESPONSIVE SIGNAL COORDINATIONSIGNAL COORDINATION

Purpose of Presentation

Provide an overview of the capabilities of traffic responsive master controllers operating full traffic actuated intersectionsPresent a few of the differences between adaptive and traffic responsiveSuggestions for setting up a traffic responsive systemTO GET THE OWNERS OF TRAFFIC RESPONSIVE MASTERS TO USE THEM!

Definition of a traffic signal

A traffic signal is a device that allows traffic engineers to leave

their intelligence at an intersection to operate it in their absence.

My perspective

I have designed and operated over 40 traffic responsive arterial coordination systems consisting of full traffic actuated intersections. Most were on suburban arterial roadways with speeds in the 50 to 60 mph range

Arterial coordination systems in the Minneapolis suburbs

50 +MPH

40- 45 MPH

Under 40 MPH

Audience poll

How many people here are operating or have operated traffic responsive systems?Are these systems also operating with full traffic actuated intersection controllers?How many are on roadways with speeds above 50 miles per hour?Anyone used this type of system in an urban grid?How many people here are currently running an adaptive control system?

Why the poll?

I am always willing to stand trial before a jury of my peers. However, I do want to make sure that I am in the presence of one.

Definitions

- Traffic responsive master controller also known as “closed loop”– Has a library of prepared system timing plans – most

systems are capable of 100 + plans– Variables

• Cycle length, Offset, Splits, Grouping– Plan selection based on

• Volume levels, Directional distribution, Speed, Other inputs

• Full traffic actuated controller – – Vehicular and pedestrian phases are enabled by

detection. Vehicular phases are also extended by detection.

Definitions

• Coordination– Merely a series of force offs and holds

applied in an organized (presumably logical) manner to provide optimal flow through a group of traffic signals

• Optimal– Like beauty, it is defined by the “eye of the

beholder”

• Early 1950’s – the 1022 controller with platoon carryover effect – Actually primitive adaptive control

• 1960’s – electro-mechanical technology– Pre-timed controllers used as coordinators– Mn/DOT uses mutual coord device for 2 to 4 intersection systems, which creates a

virtual single controller• Late 1960’s - First solid state master controllers

– Mn/DOT insists on full actuated operation & uses leased phone lines for some two-way communication

• Early 1970’s– Mn/DOT master controller cabinets are full ATR’s with data recording systems– Digital master controllers with digital coordinators

• Late 1970’s – microprocessors and development of improved timing software

– Microprocessor master controllers and microprocessor coordinators– Type 170 controllers

History of the traffic responsive & adaptive systems (at least that part that I can remember)

History (continued)

• Early 1980’s – Second generation microprocessor controllers with

internal coordination and precise time clocks also allows wider use of time based coordination

– All temperature modems allow dial-up systems and give us the “closed loop” system as we know it today

– Use of personal computers and Type 170’s as master controllers

• Mid 1980’s– Use of arterial masters in urban networks

• Duluth• Peoria• Others

History (continued)

• 1980’s and beyond - Adaptive control systems are developed and deployed– SCOOT, SCATS, UTOPIA

– TRAC

– RT Tracks (OPAC, Rhodes and others)

– City of Los Angeles

• After 1980 - for traffic responsive systems– Development of area wide supervisory systems

– Increased system capabilities

Sample equipment ca. 1970

Comparison of Systems

Arterial Signal Control Theory

Intersections per minute of travel time

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Low

Isolated – full actuated

Rigid coordination

Responsive or adaptive

Signal Control Theory

Intersections per minute of travel time

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High

Low

Signal control is adapted to traffic

conditions

Traffic is adapted to signal control

Responsive and Adaptive Objectives

• Adaptive control systems – Minimize stop delay by optimizing splits and reducing cycle

lengths– Stops are minimized through offset “optimization”

• Traffic Responsive systems– Stop delay is reduced by cycle length selection and split control– Stops (particularly high-speed) are minimized by strict offset

control and cycle length control

• Oversimplifications– Adaptive minimizes stop delay, responsive minimizes stops– Adaptive works best in an open network of “equal” roadways,

responsive works best on a high speed arterial or in a grid of regularly spaced intersections

Responsive and Adaptive Adjustments

CYCLESCY

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Understanding delay(not handled adequately by the HCM)

• Delay is the time to traverse an area that is addition to the time it would take at the normal travel speed

• Delay consists of: – Added path length (example: a loop ramp has a longer travel

path than a directional ramp)– Geometric delay – traffic must slow because of intersection

geometry (example: a roundabout)– Control delay – this has two components

• The initial imposition of the control (example: a stop sign)• Delay because of a division of intersection capacity

– Congestion delay – travel time added because of the interaction of the vehicles in the traffic stream

• Speed differentials – cars versus trucks• Different driver behavior

Understanding delay• Lost time for stopping

– A car - 30 MPH to stop to 30 MPH loses 12 to 15 seconds over traveling at a consistent 30 MPH

– A truck losses 30 to 35 seconds– For 55 MPH a car loses 25 to 30 seconds– A truck at 55 loses 60 to 80 seconds (as do any

vehicles behind that truck)• If delay is $13 for cars & $21 for heavy commercial

vehicles at 7%, then a 30 MPH stop is worth $0.058• A 55 MPH stop is $0.121• Vehicle stopping costs are $0.045 and $0.15 for cars

and trucks at 30 MPH and $0.085 and $0.30 for cars and trucks at 55 MPH

• Total cost of stop $0.11(30) and at $0.22 (55)• Idling delay is $0.22/min and fuel adds another $0.03

for a total of $0.25

Implications

• At high speeds, reducing mainline stops by adding delay to the side street is typically justified.

• Early versions of the HCM virtually ignored lost time due to stops and assigned it a value of 30% of other intersection delay.

• At 55 MPH and with V/C ratios of .5 to .6 “snappy timing” can cause lost time due to stopping to be 2/3 of the total delay. For a high-speed approach near capacity, lost time for stopping would be still be over 40%.

Traffic responsive system capabilities

• Master controller:– Uses a library of prepared system timing plans

• Most systems are capable of 100 + plans– Variables

• Cycle length• Offset• Splits – real time with actuated controllers• Grouping• Crossing artery synch

– Plan selection based on• Volume levels & directional distribution• Speed• Time of day• Special detection & other inputs

– Serves as a communication hub and allows remote intersection monitoring and timing plan changes

Adaptive system capabilities• Central controller:

– Processes data and is home to the “algorithm”– Coordination is “real time”

• Infinite plans– Communication hub with some monitoring– May have an emergency backup fixed plan– Variables

• Splits• Cycle length• Offset• Grouping

– Adjustments are based on prediction of arriving traffic:• Size of platoon • Turn percentages• Arrival time

Adaptive – Responsive infrastructure comparison

Items Adaptive ResponsivePreliminary efforts Training, setup and

calibrationTraining and development of timing plans

Central control system Central computer hosting algorithm

PC and on street master

Communication Dedicated Dial up

Detection Depends on system Normal intersection

Controllers Depends on system Off the shelf

Software Proprietary license fees or FHWA

Competitive - NEMA or 170

In operation Set and forget ??? Periodic plan updates

Incident management Adapts to handle Call for special plans

Adaptive – Responsive comparison of operation

Items Adaptive ResponsiveCycle lengths Infinite 6 or more

Splits Infinite, but small adjustments per cycle

Multiple, plus add’l max. plus queue response

Minimum split Peds plus yellows & all reds Peds treated as exceptions

Offsets Infinite 5 or more

Dilemma zone protection

Not with SCOOT & SCATS With actuated operation

Phase order changes Difficult or impossible Readily changed

In operation Set and forget ??? Periodic plan updates

Incident management Adapts to handle Call for special plan(s)

Transit priority Priority control required Great for timetable operation

High speed flow All vehicles are equal Coordination favors the mainline

Arterial time-space diagram¼ mile spacing - 45 mph progression speed – 120 second cycle

Lead – lag lefts

Lag - lead lefts

Lead lefts

Arterial time-space diagram1/2 mile spacing - 50 mph progression speed – 75 second cycle

Time-space (busway)

N

Stated objections to traffic responsive control

• Labor to develop and maintain timing plans• Expertise required to setup system• Rigid cycle lengths• Slowness of response to changing conditions• Early releases causes coordination problems• Funding is available to install adaptive control,

funding may not be available to hire staff for operating a traffic responsive system

Actuated mainline green in coordination

Added front end green from unused phase time and force-offs

moved forward

Added mainline green from no call on following phases and force offs held in place

Coordinated green

Mainline extension

TR Systems Setup Issues

• Understand what detection your master controller will have available to make its plan selection– Where is capacity an issue– Where is directionality of flow an issue– Detection to determine offset and cycle length

may be at different locations

TR Systems Timing Issues• System timing plans should cover a range of

representative conditions, not be a collection that is simply created from computer solutions that are based on data snapshots – Round off traffic data– Chart the day’s expected flows and fluctuations – Check the “natural” cycle lengths– Constrain software for best solutions within cycle

length ranges

TR Systems Timing

• Create plan library to handle the range of traffic conditions

• Create timing plans for saturated conditions• Create timing plans for incidents • Determine the “free to coordinated” threshold (about

100 vehicles per lane per hour)• Test plans to see which conditions overwhelm and at

which point they are sluggish • Outline a typical daily schedule of which plans are in

use at which times • Look at how offset adjustments and cycle length

changes will be made. Have major changes occur at the most congested intersection

The future of arterial systems

• Modern adaptive control and traffic responsive control are not far apart

• Eventually, several adaptive control algorithms will reside in a system and be available for use when needed. This is similar to what happens today with systems that switch between TOD & TR

• Adaptive control algorithms will use normal detector locations or use alternate detection locations with video detection

Observations and lessons learned

• Hardware and technology can only go so far, you still need quality people

• Early release is considered a “problem” for a traffic responsive arterial system. For adaptive control it’s considered a “feature”

• If you can understand it, it’s obsolete

ADAPTIVE…SHMADATIVE