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    Introduction to Transportation

    Systems

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    PART I:CONTEXT,

    CONCEPTS ANDCHARACTERIZATION

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    Chapter 7:

    Transportation Systems: Key Points 11-17

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    Direct Elevator Service

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    4Figure 7.1

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    Another Elevator Configuration605040302010

    1 2 3 4 5 6Figure 7.2 5

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    What configuration of elevators

    makes the most sense?

    What is the basic trade-off here

    from the viewpoint of the building

    owner?

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    Key Point 11: Infrastructure

    Shape

    The shape of transportationinfrastructure impacts the fabric of

    geo-economic structures.

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    Key Point 12: Costs, Prices

    and LOS

    The cost of providing a specific service, the

    price charged for that service, and the level-of-service provided may not be consistent.

    For example, in a bus network, the routes

    affect who gets better and worse service.

    If the urban bus system charges the same fare

    for all customers who experience different

    levels-of-service, there may be inequities. Inthinking about transportation systems design,

    we must consider who benefits and who pays

    for the system.8

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    Key Point 13: Cost of

    Service

    The computation of cost forproviding specific services is

    complex and often ambiguous.

    For example, if a passenger train

    and a freight train both use the

    same rail line, how do we allocatethe maintenance costs for that line

    to passenger and freight service?

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    Illustrating the Cost/LOS

    Trade-off

    Elevator Dispatcher Policy

    NUMBER OF PASSENGERSNEEDED TO DISPATCH

    TIME

    (12)

    1 2 3 4 5

    (6)

    (minutes)

    10Figure 7.3

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    Illustrating the Cost/LOS

    Trade-off(continued)

    Passenger Arrival Pattern

    NUMBER OF PASSENGERSNEEDED TO DISPATCH

    PASSENGERARRIVALPATTERN

    DISPATCH

    1 2 3 4 5 TIME

    (12)

    (6)

    (minutes)

    11Figure 7.4

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    Building a TrainA

    BD

    E

    C

    With trains coming in from stations west, we buildan outbound train that will have cars from many

    different inbound trains. When do we dispatch thetrain from the terminal? We are balancing theLOS for the cars already on the outbound trainwith those that have not yet arrived.

    Also, the longer the train, the smaller the cost/car.

    12Figure 7.5

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    Key Point 14: Cost/Level-of-

    Service Trade-offs

    Cost/level-of-service trade-offs are a

    fundamental tension for the

    transportation provider and for thetransportation customer, as well as

    between them.

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    Key Point 15: Demand

    Consolidation

    Consolidation of like-demands isoften used as a cost-minimizing

    strategy.

    For example, when an airline runs

    a hub-and-spoke operation, it is

    consolidating people from differentorigins who have common

    destinations into airplanes to lower

    costs.14

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    Lumpy InvestmentsCapacity of Elevator System

    CAPACITY

    1 2 3 4 5 NUMBER OFELEVATORS

    15Figure 7.6

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    Key Point 16: Lumpy

    Investment

    Investments in capacity are often

    lumpy (e.g., infrastructure).

    Capacity of

    Single vs.Double TrackRail Line

    Figure 7.7

    SIDINGS

    SINGLE TRACK(OPERATIONS IN BOTH DIRECTIONS )

    WESTBOUND

    EASTBOUND

    DOUBLE TRACK

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    Another Elevator

    Configuration

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    Figure 7.8 17

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    Capacity vs. Number of

    BusesCAPACITY

    NUMBEROF BUSESThis is lumpy, but there are so manyvehicles, we can approximate the

    relationship as smooth (linear).18Figure 7.9

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    Think of resources and think of

    investments in capacity in a verybroad way. (Refer back to Key

    Point 2: Transportation -- part of a

    broader system.)

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    Capacity vs. Cost

    CAPACITY(PASSENGERS/HOUR)

    1 2 3 NUMBER OFELEVATORS

    We can have inexpensive, low-capacitysystems or more expensive, high-capacitysystems. Making decisions about whichsystems we need or want is a continuing

    theme in transportation.

    Figure 7.10 20

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    The concept oflevel-of-service is

    related to the cost and capacitytrade-off. The level-of-service

    provided by the transportation

    system is a function of the volumebeing carried by that transportation

    system (see Key Point 9:

    Transportation Supply).

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    Typical Supply Functions

    LEVEL OFSERVICE

    SYSTEM

    CAPACITY1 SYSTEMCAPACITY2

    CAPACITY(LUMPY)

    VOLUME

    Often, there is a precipitous fall-off in level-of-service as the volume approaches capacity,

    sometimes called a hockey stick.22

    Figure 7.11

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    Key Point 17: Capacity, Cost

    and Level-of-ServiceThe 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.If we underinvest in capacity, our level-of-service

    may 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 oftransportation system design.

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