Adaptive Signal Control Technology: Bringing a Systems Approach to Implementation and Evaluation

October 18, 2011

Kevin Fehon, P.E., PTOE

DKS Associates

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Overview

The past 40 years of adaptive signal systems The last five years in the USA Breaking out in 2011 Bringing a structure to system selection Performance Evaluation

First a definition

ASCT – Adaptive Signal Control Technology Terminology adopted by FHWA Used to refer generically to adaptive traffic signal

systems Avoids confusion with ACS-Lite

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The past 40 years

It all started with SCATS in 1973 and SCOOT in 1975

Two fundamentally different but practically-oriented approaches

Both widely accepted outside the USA by 1985 Different approach attempted in USA, reflecting

different administrative and economic environment

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SCOOT 2009

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SCATS 2009

53 Cities; 179 Signal Regions

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What has held up acceptance in the USA?

Agency capability and willingness System performance and benefits Lack of understanding Cost Availability of US-based systems

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Growing acceptance in the USA.

ASCT is an important element of FHWA’s Every Day Counts (EDC) program

Increasing number of jurisdictions considering ASCT

Modern equipment with more processing power New ASCT systems emerging Still less than 1% of USA signals

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US Adaptive Systems, April 2011

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Systems currently available in USA

SCOOT/TACTICS SCATS InSync LADOT ATSC ACS-Lite OPAC KHAdence

QuicTrac RHODES Balance Synchro Green RHODES ATMS.now Delcan & Intellight

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Introducing a structured approach to ASCT system selection

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What is an appropriate definition of “adaptive”? Many different definitions are acceptable The definition you choose should be the one that

suits your circumstances How do you define real-time? Is it predictive or

reactive or both? What parameters are “adaptive”?

What are you trying to achieve with ASCT?

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Different coordination strategies

Most coordination strategies can be categorized in one of the following four ways: Pipeline along a route (arterial or within grid) Progression in two directions along a route Equitable service for adjacent land uses Queue management

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Non-coordination strategies

Some adaptive strategies do not involve coordination Optimal operation of an isolated intersection Optimal operation of a single critical intersection

within a coordinated area

Why use a systematic process?

Why SE?

Understanding the problem Managing risk

Projects getting bogged down with shifting requirements

Acquisitions being challenged by unsuccessful bidders/proposers/vendors

Projects not meeting agency needs (and it is mandatory for federal-aid projects)

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Are you fully expressing your desires?

Is ASCT really what you need? Can you clearly document the deficiencies of

your existing system that you wish to overcome with adaptive?

Can you clearly document the existing capabilities of your system that must be retained with adaptive operation?

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Can you clearly verify that you got what you asked for? Are your needs clearly expressed? Is each need translated into a requirement Is every requirement actually satisfying an

expressed need? How is each requirement tested, so the that the

vendor can verify it is satisified?

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Can you validate that you got what you needed? Have your organization’s goals and objectives

been clearly defined? Are measures of performance clearly defined? Can you test the operation against the measures

of performance?

What is the purpose of the Model Systems Engineering Documents?

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Provide a framework to guide agencies to the most appropriate solution Provide sample statements that can be used in a

Concept of Operation Provide sample requirements that can be used to

select/purchase/design a system Describe appropriate verification and validation

plans

How should your process work?

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Overview

First pass in half to one day, by experienced agency staff

Identify additional information you need in order to make appropriate decisions and document the basis of those decisions

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Work Flow

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What are the pitfalls of not following a structured approach?

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Pitfalls

You don’t get the most suitable system You may lose some capabilities You may not get the system you want Making a constraint a requirement at the outset

distorts the outcome. You can’t quantify the trade-offs you are making

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The structured approach will result in the most appropriate ASCT selection Required capabilities will be clearly stated Assumptions will be explicit, so requirements

won’t fall through the cracks Trade-offs to satisfy real and perceived

constraints will be explicit and justified Expectations are more likely to be met

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Is it worth the effort?

Emphatically yes! Some ASCT systems that have not fulfilled

expectations are falling by the wayside The established systems have strongly

documented benefits and high B/C ratios Much misinformation, both positive and negative

Gresham PM Peak TT(Eastbound Burnside)

405

368

424393

349 373

314

0

100

200

300

400

500

Trav

el T

ime

(sec

)

1997 Free

1998 TOD

2004 Free

2004 (1998 TOD)

2004 TOD

2007 (2004 TOD)

2007 SCATS

Legend

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Evaluation techniques often hide the truth

Travel time per direction does not show system-wide effects, and confuses positive and negative impacts.

Travel time per period do not show effects of varying demand levels.

Volume-weighted, system-wide evaluation allows differentiation of conditions.

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Sunnyvale: System Expansion

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Questions?