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Introduction to Transportation

Systems

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PART I:CONTEXT,

CONCEPTS ANDCHARACTERIZATION

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Chapter 10:Models and Frameworks

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Models and Frameworks:

An IntroductionModels are mathematical

representations of a system.Frameworks are qualitative

organizing principles for analyzing

a system.

We can use both models and frameworks to do analysis.

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What is our function as

transportation professionals?

Designing better transportationsystems

Using resources, financial andotherwise, effectively in atransportation context

Operating transportation systemsoptimally

Maintaining transportation systemsefficiently

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Value-laden words:

bettereffectivelyoptimallyefficiently

These depend on your point of view.

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A Structure for Transportation

System Analysis

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LOOP 1: Does the evaluation suggest other alternatives?

LOOP 2: Are the measures of effectiveness appropriate?

Figure 10.1

A Systems Analysis Framework:A First Look

Search foralternatives in the

real world

Prediction ofperformance,

flows, etc.

Evaluation of

alternatives

Reconsider

measures ofeffectiveness

Selection amongalternatives

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The Subtlety in ChoosingMeasures of Effectiveness

Be sure your measures of effectiveness

are goodAn Urban Area

High Income Low Income

Area Area

CenterCity

I II

Figure 10.2 9


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A Systems Analysis Framework:A Second LookSearch for

alternatives in thereal world

Abstraction of realworld into

model / framework


flows, etc.

Evaluation ofalternatives

Reconsidermeasures ofeffectiveness


2

3

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LOOP 3: Is the abstraction good at predicting?

We need to ask, Is the abstraction any good?10

Figure 10.3


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A Systems Analysis Framework:A Third LookSearch for

alternatives in thereal world


model / framework


flows, etc.


Reconsider

measures ofeffectiveness


Insight:Better understandingof system behavior

2

3

1



LOOP 3: Is the abstraction good at predicting?

11Figure 10.4


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Why Are We Modeling?

Choosing the Best Alternative --Optimization

System Operation

Learn from Model Building Processes Insight

We may gain insight into complex

situations by first understanding simplersituations resembling them.

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Modeling for Negotiation

Prodyut Dutt, in A Standards-BasedMethodology for Urban Transportation Planning

in Developing Countries, focused on howplanners work in developing countries versus

the way urban planners work in the developed

world. The essence of his research looked at

the differences in planning methodologiesnecessary in the two environments.

Dutt developed models for negotiation -- theidea oftransparentmodels, where rather thanshielding the outside world from what was going

on within that black box model, planners could

look into the model and clearly see the

assumptions driving the trade-off about locationof corridors in urban areas.13


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The Model Is a Shaper of

Your World View

A hammer is a fine tool, but it is not very good for washing windows.

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Modeling Approaches

Network AnalysisLinear ProgrammingNon-linear ProgrammingSimulationDeterministic Queuing

Probabilistic QueuingRegressionNeural NetworksGenetic AlgorithmsCost/Benefit AnalysisLife-cycle Costing

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Modeling Approaches (continued)

System Dynamics

Control Theory

Difference Equations Differential Equations Probabilistic Risk Assessment Supply/Demand/Equilibrium Game Theory Statistical Decision Theory Markov Models

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Getting Answers from ModelsDeveloping a model -- an abstraction -- and

getting results from it are two different things.

Search foralternatives in the

real world


model / framework


flows, etc.


Reconsidermeasures ofeffectiveness


Insight:Better understandingof system behavior

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3

1

Can the model be

solved -- i.e.,produce results?

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LOOP 1: Does the evaluation suggest other alternatives?LOOP 2: Are the measures of effectiveness appropriate?

LOOP 3: Is the abstraction good at predicting?LOOP 4: Develop new abstraction.

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Models vs. Frameworks

ModelsModels are a mathematical

representation of reality --quantitative in nature.

FrameworksWhen we talk about a framework,

we are generally talking about a

qualitative view of a complexsystem. It is a way of thinking --a way oforganizingour thinkingabout a complex system.

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Here is a framework we discussed earlier:

Urban Intercity Inter-national

Public Ownership/

Operation

Private Ownership/Operation

Joint Ownership/

Operation

Traveler/Pax

Freight

Figure 10.6 19


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Simple vs. Complex Models

and Frameworks

MODEL FRAMEWORK

(Quantitative) (Qualitative)

SIMPLE

COMPLEX

Useful

Not Useful

Useful

Not Useful

Useful

Not Useful

Useful

Not Useful

Figure 10.7 20


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Points for Class Discussion

Public TransportationNational Transportation PlanTraffic Light Coordination

What kinds of models and

frameworks would you use in each

of these cases?

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