trans sys chap07
TRANSCRIPT
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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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60
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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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