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1.221J/11.527J/ESD.201J Transportation SystemsFall 2004

LECTURE 5

DISPLAYS

SPEAKER: Joseph M. Sussman

MIT

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The Elevator ExampleElevators are simple compared to some of the

more complex transportation systems, but they

can be instructive and illustrative.

With this simple example we can gain insight intooverall system behavior that we can apply to

more complex systems.

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Elevator System60.......1

ELEVATORS A B CFigure 6.1

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Key Point 6: Transfers

Intermodal and intramodal transfers are key

determinants of service quality and cost.

Transfers between elements of the

transportation system are often inefficient.

In the elevator example, a transfer from the

walk-mode as one comes into the building,to the elevator-mode, implies some waiting

and, hence, some inefficiency.

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Key Point 8: Capacity

Capacity is a complex, multi-dimensional

system characteristic affected by:infrastructure

vehicles

technology

labor

institutional factorsoperating policyexternal factors (e.g., clean air, safety,

regulation)

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Key Point 8: Capacity (continued)

In the elevator example, We could increase the number of

elevators.

We can also change vehicletechnology. For example, we could

have larger or faster elevators.

We could have capacityimprovements as a result of control

technologies and smarter algorithmsfor dispatching.

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Key Point 9: SupplyLevel-of-service = f(volume); Transportation Supply. As

volume approaches capacity, level-of-service deteriorates

dramatically -- the hockey stick phenomenon.

LOS vs. Volume: The Hockey Stick

LOS

HOCKEYSTICK

CAPACITY

VOLUME

Figure 6.37

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Direct Elevator Service

8

605958

............210

Figure 7.1

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Another Elevator Configuration

60

50

40

30

20

10

1 2 3 4 5 6Figure 7.2

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What configuration of elevators makes the mostsense?

What is the basic trade-off here from theviewpoint of the building owner?

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Key Point 11: Infrastructure Shape

The shape of transportation infrastructure

impacts the fabric of geo-economic structures.

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Key Point 14: Cost/Level-of-ServiceTrade-offsCost/level-of-service trade-offs are afundamental tension for the transportation

provider and for the transportation

customer, as well as between them.

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Key Point 15: Demand ConsolidationConsolidation of like-demands is often used as a cost-minimizing strategy.For example, when an airline runs a hub-and-spoke operation, it is consolidating people from different origins who have common destinations into airplanes to lowercosts.

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Key Point 16: Lumpy InvestmentInvestments in capacity are often lumpy (e.g.,

infrastructure).SIDINGS

Capacity ofSingle vs. Double Track Rail Line

WESTBOUND

EASTBOUND

(OPERATIONS IN BOTH DIRECTIONS )SINGLE TRACK

DOUBLE TRACK

Figure 7.7 14

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Key Point 17: Capacity, Cost andLevel-of-Service

The linkages between capacity, cost and level-of-

service -- the lumpiness of investment juxtaposedwith the hockey stick level-of-service function as

volume approaches capacity -- is the central

challenge of transportation systems design.

If we underinvest in capacity, our level-of-servicemay be uncompetitive. If we overinvest, level-of-

service may be fine, but costs will be high and our

prices may not be competitive. Making this

decision, faced with lumpy investments and the

hockey stick LOS/volume relation, is difficult

indeed. This leads to the central challenge of

transportation system design.

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Our Next Concept -- PeakingVolume vs. Time of Day

-UP

VOLU MEARRIVINGAT WORK

RETURN FROM

LUNCH PEAKPACKAGEPICK

TIME OF

7 AM NOON 4 PM DAY

UP DIRECTION

VOLUME

K

LEAVING

WORGOING TO

LUNCH PEAK

7 AM NOON 4 PM TIME OFDAY

DOWN D IRECTION

16Figure 8.1

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How much capacity should we provide?Different Capacity Decisions

VOLUME

CAPACITY1

CAPA Y3

CAPA Y2

=

CIT

CIT

AVERAGE

DEMAND

TIME O F DAY

So what do we do? We cannot choose such a low capacity that

customer levels-of-service during peak periods are unacceptable.

At the same time, however, we cannot provide a level-of-service

such that nobody ever has to wait-- its not economical. So, capacity3 may be a good

compromise. The question of design capacity and how we

accommodate temporal peaks in demand is Key Point 18.

Figure 8.2

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Key Point 18: Peaking

Temporal peaking in demand: a fundamental issue is design capacity -- how often do we not satisfy demand?

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Our Next Concept

The volume that a transportation serviceattracts is a function of the level-of-serviceprovided to customers. If the level-of-service

deteriorates, less people will want to use the

service.

This is simply a micro-economic concept.For example, if a movie theater doubles its

price, therefore making its service less

attractive -- in this case, more expensive -

fewer people will go to that movie theater. Ifa movie theater halves its price, more people

will go.

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Key Point 19: Volume = (level-of-

service); Transportation DemandTransportation Demand: LOS vs. Volume

LOS

DEMAN D

VOLUM E

Figure 8.3

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Key Point 21: Different Time ScalesDifferent transportation systemcomponents and relevant external

systems operate and change at different

time scales, e.g.,

Short run -- operating policy

Medium run -- auto ownership

Long run -- infrastructure, land use.

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Equilibrium between Supply and

Demand Level-of-service is a function of volume. As

a facility gets congested, the level-of-service

for customers deteriorates, as discussed in

Key Point 9.

But, as level-of-service changes, demandchanges as well. Demand increases aslevel-of-service improves and decreases as

level-of-service deteriorates.

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Key Point 22: EquilibriumLEVEL OF

SERVICE

*

v*

DEMAND

SUPPLY

LOS

VOLUME

Equilibration of transportation supply anddemand for transportation service to predictvolume is a fundamental network analysismethodology.

Figure 8.423

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The Mechanics of Supply/DemandEquilibrium

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Iteration to Find EquilibriumLEVEL OFSERVICE

DEMAND

1

2

V*, *

S

LOS

LOS

LO S

UPPLY

v1 v3 v2 VOLUME

v

v1 -- first guess at volume

LOS1 implies demand v2

2 implies LOS2

LOS2 implies v3 , etc., until v*, LOS* are found.

Figure 8.525

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Changing SupplyLEVEL OFSERVICE

D

**

*

S 2

EMAND

LOS

LOS

UPPLY

SUPPLY1

V* V** VOLUME

People respond to incentives. If highwaytransportation becomes cheaper, people buy

more.

Figure 8.626

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Equilibrium: A Second LookLEVEL OFSERVICE

DEMAND1

DEMAND2(AFTER ACTIVITYSHIFT)

AFTER NEW

CONSTRUCTION)

*

S 2(S

1

LOS***

LOS

UPPLY

UPPLY

VOLUME

Figure 8.9 27

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Increased Volume: Better or Worse?

So, at a higher volume, the customers are seeingthe same level-of-service. Are we worse or

better off than we were before we started?

CLASS DISCUSSION

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Key Point 26: Stochasticity

Stochasticity -- in supply and demand -- ischaracteristic of transportation systems.

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StochasticityStochasticity in traffic volume is differentthan peaking.

VOLUME

STOCHASTIC VARIATION IN PEAK

3,000

AVERAGEAM

PEAK

TIME

Figure 9.1 30

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Measuring Transportation System

Performance What do your customers perceive?Our ways of measuring performance have to

relate to the ways in which our customers make

decisions about whether to use us or our

competitors.

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Performance Measures and Cost

A second concept is that performance measures have torelate to costs of operations and revenues derived from

operations of those systems.

The customer cares about system performance (e.g.,overall travel time), but

A third concept: System vs. Component Performance.The operation is often managed on a component basis.

The hope is, if we do a good job of operating thecomponents, the system as a whole will operate well.

Usually, it is a necessarycondition that component

operation be effective for system operation to be

effective, but it is very often not a sufficientcondition. We

can have a poorly meshed system in which thecomponents are operating well, but the system

performance is still poor.

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Key Point 28: Performance MeasuresPerformance measures shape transportation

operations and investment.

CLASS DISCUSSION

Some examples from transportation systems you

are familiar with.

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Key Points -- Summary (1)1. People and organizations alter behavior based on transportation

service expectations.

2. Transportation service is part of a broader system -- economic,social and political in nature.

3. Competition (or its absence) for customers by operators is acritical determinant of the availability of quality transportation

service.4. Analyzing the flow of vehicles on transportation networks, and

defining and measuring their cycle, is a basic element of

transportation systems analysis.

5. Queuing for service and for customers and storage forvehicles/freight/travelers, etc., are fundamental elements of

transportation systems.

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Key Points -- Summary (2)6. Intermodal and intramodal transfers are key determinants of

service quality and cost.7. Operating policy affects level-of-service.8. Capacity is a complex, multi-dimensional system characteristic

affected by: infrastructure vehicles

technology labor institutional factors operating policy external factors (e.g., clean air, safety, regulation)

9. Level-of-service = (volume); Transportation Supply. As volumeapproaches capacity, level-of-service deteriorates dramatically -the hockey stick phenomenon.

10. The availability ofinformation (or the lack) drives system

operations and investment and customer choices. 35

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Key Points -- Summary (3)11. The shape of transportation infrastructure impacts the fabric of

geo-economic structures.

12. The cost of providing a specific service, the price charged for thatservice, and the level-of-service provided may not be consistent.

13. The computation of cost for providing specific services is complex

and often ambiguous.

14. Cost/level-of-service trade-offs are a fundamental tension for thetransportation provider and for the transportation customer, as

well as between them.

15. Consolidation of like-demands is often used as a cost-minimizing

strategy.

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Key Points -- Summary (4)16. Investments in capacity are often lumpy (e.g., infrastructure).17. The linkages between capacity, cost and level-of-service -- the

lumpiness of investment juxtaposed with the hockey stick level-of-service function as volume approaches capacity -- is the

central challenge of transportation systems design.

18. Temporal peaking in demand: a fundamental issue is designcapacity -- how often do we not satisfy demand?

19. Volume = (level-of-service); Transportation Demand.20. Level-of-service is usually multi-dimensional. For analysis

purposes, we often need to reduce it to a single dimension, which

we call utility.

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Key Points -- Summary (5)21. Different transportation system components and relevant external

systems operate and change at different time scales, e.g., Short run -- operating policy Medium run -- auto ownership Long run -- infrastructure, land use

22. Equilibration of transportation supply and demand for transportationservice to predict volume is a fundamental network analysis

methodology.

23. Pricing of transportation services to entice different behavior is amechanism for lowering the negative externalities caused by

transportation users on other users and society-at-large.

24. Geographical and temporal imbalances of flow are characteristic intransportation systems.

25. Network behavior and network capacity, derived from link and nodecapacities and readjustment of flows on redundant paths, are important

elements in transportation systems analysis.

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Key Points -- Summary (6)26. Stochasticity -- in supply and demand -- is characteristic of

transportation systems.

27. The relationship among transportation, economic development,and location of activities -- the transportation/land-use

connection -- is fundamental.

28. Performance measures shape transportation operations and

investment.29. Balancing centralized control with decisions made by managers

of system components (e.g., terminals) is an important operating

challenge.

30. The integrality of vehicle/infrastructure/ control systemsinvestment, design and operating decisions is basic to

transportation systems design.

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