Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 73
TCRP H-12 Final Report
4~0 6`FUNCTIONAL DESIGN,, OF AN INTEGRATED URBAN MODEL
4.! Introduction
Having built the case In Me preceding chapters for We need for integrated urban models, this
chapter develops a general design of art 'ideal" integrated urban model. This is viewed as a critical
step in the development of improved operational models for two reasons. First' the "ideal" model
provides a consistent benchmark against existing models can be compared (Chapter 51. Second. it
provides an explicit target towards which research and development (R&~) efforts can be directed
(Chapter 69.
The development of the ideal mode} design proceeds in several steps. Section 4.2 provides
a high level overview ofthe ideal system. Section 4.3 defines a set of design issues which need to
be addressed in turning this conceptual overview- into an operational model, while Section 4.4
discusses the closely associated issue of criteria for assessing a model's performance. Section 4.5
develops a more elaborated descup~on of the ideal mode] by addressing each of the design criteria
developed in Section 4.2 in some detail. While far from an operational specification (something
which is well beyond the scope of this project), the mode] description presented in Section 4.5 is
sufficient for current purposes of assessing the current state of modeling practice and of defining a
sensible R&D program in this area.
4.2 Overview of An Idealized, Integrated Modeling Process
Figure 4. ~ presents a highly idealized representation of a comprehensive transportation
land-use modeling system. The "behavioral core" of this system (shaded area of Figure 4.~) consists
of four inter-relatec! components:
[anct development: this models the evolution of the built environment, and includes
both the initial development of previously "vacant" land and the redevelopment over
time of existing land-uses. This component could also be labelled "building supply"
since Bulldog StOCK Supply Actions (cons~ct1on, demolition, renovation. etc.) me
included.
· , .,, ~ , , ~ . - . . .
2. Location choice: ibis includes the location choices of households (for residential
dwellings), firms (for commercial locations), arid workers (for jobs).
3.
Activi~y/traveZ~-hether performed by traditional four-stage methods or by emerging
activit:~-based models, this component involves predicting the tup-making behavior
of the population. ultimately expressed in terms of ongin-destination flows by mode
by time of day.
- 49
OCR for page 74
TCR~ H-12 Final Report
.
Figure 4el
Idealized Integrated Urban Modeling System
Demographics ~1-
~ - ; .
~ Regional Economics ~ ~ :~ ~ ~ ~-~;~
- i. ::
: -::: ~
~ Government Policies 1 - ~ ~ If.: ~
: : : : : ::
.. ..
.. .
Auto Ownership
-, j
Transport.System *- A
!
. ~ ~
.. ~ ~
.... ~ .. ~ .. ...
. . .... .. ~ .....
Land Use ~... : ~
.~ . . I. ~
.. .....
... .. . ..
- ' '~;:~ '1
. .
~ -:: ~ -; ' 1
: :: ~ .. . ~ -.:~ ~ ~1
2: it- ~ ~!
e - ~ ~
~ - .~ I. ~
':::::':'2~'':1
~ ~ ~::--1
Activity / Travel and .- ~ -I ~-
(-J`,ods Movement ~ ~:~ :~ I: it: ::
Location Choice
~. . -.
....
- . - ~ ~
. ...
:::
· ;.
· . ..
_~._ - _
_._
Flows, Times, etc. | | ExternalImpacts
- sO
OCR for page 75
TCRP H-12 Final Report
Auto ownership: this component models household auto ownership levels -- an
important dete~minar~t of household travel behavior.
Points to note concerning these four "behavioral core" components include the following:
In speaking about "land-use" it is common for transportation planners to blur the
ist~nchons among these four components, especially between the concepts of 1~d
development and location choice. A properly specified model, however, must clearly
distinguish among these components since they involve very different actors.
decision processes and timeframes. As is discussed further below- they also
represent distinctly different "degrees of freedom" for the system to respond to
exogenous inputs (such as construction of new transit infrastructure).
Each component involves a complex set of sub-models. In particular, market-based
supply-demand relationships tend to dominate aggregate behavior in each cased
(buyers and sellers of houses interact within the housing market; workers and
employers interact within the labor market; etc.), with prices) both being
endogenously dete~nined and playing a major role in determining the outcome of
these supply-demand interactions. Models which ignore these major supply-demar~d
interactions may fall to properly capture the dynamical evolution of We urban system
over tone.
.
.
A simple flowchart such as Figure 4.] never properly captures the temporal
complexities of a dynamic system. The vertical hierarchy is chosen to represent
shorts conditioning effects. That is, In the short run, most location choices are
made within a "fixed" building stock supply. Similarly, in the short run, most
activity/~avel decisions are made given a "fixed" distnbution of activity locations
(and a fixed number of household autos). In the longer run, all four components
evolve' at least partially In response to "feedback" Tom lower levels in the hierarchy
(land-use evolves in response to location needs of households and firms, people
relocate Weir homes armor jobs at least partially in response to accessibility factors;
etc.~.
The inclusion of auto ownership as a separate box within the "behavioral core" is
somewhat unconventional. Auto ownership is often treated as simply one more
(ofren exogenously determined) input to We travel model. As Ben-Akiva tI 974] has
4 With the possible exception of the auto ownership component, although even here a "supply side" clearly
exists, even if we usually choose not to model it explicitly.
Or, in the case of trip-making, travel times
- 31
OCR for page 76
TCRT H-17 Final Report
observed, however auto ownership is an integral part of the '"mobility bundle''
(which, in terms of Figure 4. I, Ben-Akiva would define as the combination of the
location choice, auto ownership and activity/trave} components) in that it is
fundamentally interconnected with residential location arid work trip commuting
decision-making. This point is strongly reinforced within the empincal literature
discussed in Chapter 3, in which auto ownership is consistently found to be art
important "intermediate variables connecting urban form (as measured by residential
density, etc.) and Ravel behavior (as measured by transit usage, VMT, etch
As shown in Figure 4. I, there are at least four major "drivers" of urban systems:
1. Demographics: evolution of the resident population in terms of its age-sex
distribution, population size, education level, etc.;
2. Regional economics: evolution of the urban region economy in terms of its size,
industrial distribution, etc.;
3. Government policies: zoning, taxation, interest rates, etc.; and
4. The transportation system: road, transit' etc.
The extent to which these venous drivers are treated as being exogenous or endoger~ous to the model
will vary from one modeling system to another. Government policies and changes to the
transportation system are almost exclusively treated as exogenous inputs; demographic and regional
economic processes are almost always Heated as at least partially endogenous. The key point is that
the full range of "drivers" of land-use/location/travel decision-making should be included in the
modeling system to ensure that the impact of any one policy (such as a change in the transit system)
can be properly represented and evaluated by the model. In particular, it was often the case with
early land-use models that they over-emphasized transportation system effects on land-use/location
processes and hence were biased towards over-predicting the impact of transportation system
improvements on these processes. As Knight and Trygg [1977] clearly demonstrate. however,
transportation improvements are only one among many determinants of land development decisions
-(see Figure 3.39.
It is fair to say that no existing transportation - lard-use model Filly captures all aspects of
the comprehensive modeling system described above. Such a system, however, provides the starting
point for assessing both the state of the practice and the state of the art in this field. It also defines
the goal towards which all such modeling systems should be striving, in that such a system would
provide the analytical means for assessing the short and long run impacts of both transit and road
alternatives in a balanced and comprehensive way. In particular, the long run impacts of major
improvements in transit access on land development, residential and employment location choice
- 52
OCR for page 77
TChP H-12 Final Report
auto ownership levels and activity/travel could be assessed in a logical and defensible mater.
It is also fair to say that, although not incompatible with a comprehensive transportation -
land-use modeling process, TMIP is not actively developing such a process, despite the existence
of the land-use Pack ("Track E"). Research to date within TMIP has focussed on act~vityl~ravel
modeling (and associated emissions modeling), with the majority of the effort being placed on the
development of the TRANSIMS network modeling system [Barrett' et al. ~ 1 995~.
Figure 4. ~ can be expanded and reformulated ad infinitum. Figures 4.2 and 4.3 present two
independently developed designs for "next generation" navel demand modeling systems which were
generated as part of an FHWA "think piece" at the beginrung of the TMIP process. Without
discussing these designs in detail, the key point to note is that land-use, location choice and
demographics are all integral components of the proposed overall modeling systems. This inherent
integration of land-use and transportation processes is further emphasized in Wegener's
conceptualization of the process (Figure 4.4), in which he emphasizes the interactive, cyclical, feed-
back nature of Me urban system. Cornrnenting on this figure, he notes:
"The two-way interaction between land-use and transportation may be less
commonplace for transportation modelers who are trained to take the land-use
forecasts provided by planning departments as something beyond doubt. Now
transportation planners, obliged to think about the land-use impacts of their
proposals, call for land-use models as add-one to their ... models. Nothing could be
more shortsighted. The land-use transportation feedback cycle needs to work its way
through several iterations to equ~libnum or dynamic disequilibnum... The conclusion
is that if transportation planners want larld-use forecasts, they have to integrate land-
use models Into their models, or vice versa." [Wegener, ~ 99S, p. 27-28]
Figure 4.5 provides one final representation of a transportation - land-use modeling system.
The key point of this figure is to illustrate the potential sensitivity of such a system to a wide range
of land-use and transportation policies. The figure shows a representative (although not necessarily
~ - 1
exhaustive) list of policies of interest. The arrows indicate the "entry points" for each of these
policies within the modeling system, i.e., the point at which the given policy directly enters model
calculations. For example, congestion pricing, gasoline taxes, etc. directly affect road user costs and
so "enter" the modeling system at the road assignment stage, where these costs are calculated on a
link by link and O-D pair by O-D pair basis, and where these costs presumably affect auto route
choice decisions. The impact of such pricing policies, however, feeds back through the system,
potentially affecting modal choices (and perhaps other aspects of travel choice), auto ownership, and
possibly even residential and/or employment location choice. Thus, the modeling system, in
principle, is capable of capturing both short- and long-run responses to a given policy (or
combinations of policies) and, thereby, provide a more accurate estimate of system response, relative
to more partial treatments of the problem.
OCR for page 78
TCRP H-12 Final Report
Figure 4.2
SAMS: Sequenced Activity-Mobil~ty System
(Resource Decision Consultants, Inc., as reported in Spear ~19943)
>
~ l
' PLANNING
I PR( )CFRS
~;~~
\TDMs,
,
v ~ _ , ~
~ , ~ /Command & Control
. . ~ . ~
>
1
*Runs on GIS platform
URBAN SYSTEM
MICROSIMULATOR* I
Land-use
Re/development,
price, densification
Residential and
Job Locations
HIGHWAY/TRANSIT
NETWORK
SOCIO DEMOGRAPHIC
MICRO SIMULATOR*
Individuals
Households
Fi~ms/Developers
t 11
- 1 1 '1
DYNAMIC HOUSEHOLD
VEHICLE TRANSACTIONS
MODULE
~ ~ T ~
ACTIVITY-BASED DAILY
TRAVEL SIMULATOR*
onginJdestination, time of
day, mode
· vehicle allocation &
vehicle occupancy
I t
DYNAMIC NETWORK
ASSIGNMENT*
Link flour by clock time
Level of service
Cold/hot starts
.
AIR QUALITY |
EMISSIONS MODULE I
1
Indicators for Mobility,
Air Quality & Value
of Travel Services
- 34
OCR for page 79
TCRP H-12 Final Report
Figllre 4.3
SMART: Simulation Mode} for Activities, Resources and Travel
(Louisiana Transponahon Research Center, as reported in Spear t19943)
-
Land
\~Prices
-
Site Schedules/
Constraints ~ ~'l'
Land
\~ Uses J
:Infrastructure
Investments
by
-
>( Transpor~tion
\` System ,J
. ..........
Linkage proposed
Linkage suggested for later inclusion
-
Area ~ HH
no; r ~ Characteristics J
Needs/ ~ HH~
Activin- Pattern \~ Rind Constrain:
-
r M=datO~'~r
Household
Activity
Simulator
Routing
Flexible ~l
+ - 1
Optlonal
SpeedfConoestion
~ Net volumes by time of day
~ Net volumes by time of darer
1
~ Net volumes by time of day
1
(E up by link)
OCR for page 80
TCRP H-12 Final Report
Figure 4.4
The Land-Use/Transportation Feedback Cycle
Source: Wegener L1995]
Mode choice
He
Route choice
a/
/
Firm loads /
Travel times/
distance/costs
1
Accessibility
Attractiveness
-
Location decisions
of investors
-
Destination choice
Transport
Land Use
-
-
-
~~ Construction
- 56
Tnp decision
\
Car ownership
Activities
Location decisions
of users
OCR for page 81
TCRP H-12 Final Report
l
Figure 4.5
Policy Inputs into an Integrated Urban Mode}
Source: Miller and Hassour~ah t1993]
ZoninglLand Use Policies e
Interest Rates an. 9=
Housing Policies
Current Technology Changes ~
AdvancedlNew Technologies-_ . _ AVeh.Technology~AutoOwnershipt
~1
Inspection & Maintenance Programs ~
Vehicle Purchase Taxes A.
Incentives for Scrapping"Bad" Cars
Tax Policies Re. Auto Use DeductionsJ
Carpooling Policies '
Parking Policies
Telecommuting Policies
Flexible Work Hours, etc.
HOV Lanes
Congestion Pricing ~
Traffic Control Measures ~ ~ ..~.
Gasoline Taxes J
~ a.....
Transit Improvements
Transit Prionty Measures
Transit User Subsidies J
Employment
Retail, etc.
==~_t Building Stock Residential Distributiont
_ _ _
~_ _ _
, .~'' ~
_ _ _ ~
1
1
.,
Non-Work Travel: _ _
· Generation ~ .
~ by time of day
e Distribution w /weekend
- Mode Split | eekday
Auto Driver Trips
(by time of day)
(+ auto occ.)
Transit Tnps
(by time of day)
Walk/Bicycle Trips
(by time of day)
41 . .
.. ~ ~ ~ Auto Transit
! As s i Elm ent A s s i gem ent
_
~ _ , I _ _ -
~ r ~ !
Auto Energy Use Transit Energy
& Emissions Use & Emissions
~,
r I
I t=t+^t
- 57
OCR for page 82
TCRP [I-17 Final Report
-
4.3 Design Issues
4.3.! Introduction
A large number of issues must be considered in the design of an operational integrated unbars
mode} derived Mom the idealized modeling system presented In the previous sub-section. As many
as possible of these are listed In Table 4. ~ and briefly discussed below. Different models, of course,
wall address these issues In a variety of ways, ranging from ignoring them completely to dealing with
them in a very computationally detailed and/or theoretically rigorous6 mariner. No "right'
answer/approach necessarily exists with respect to any one of these issues. As with any design
exercise, the "nght" or "best" design depends on the specific application context (data availability,
computational and technical support capabilities, ar~alysis/forecasting needs, etc.~. In addition, no
one issue or "dimension" of the problem can be "optimized" in isolation; it is the overall balance
across design dimensions which is impor~t (e.~., very fine spatial resolutions may be
difficult/~mpossible/ur necessary to m~nta~n within very Tong-range forecasting applications). The
intention here, rather, is simply to generate a reasonably comprehensive list of issues, as a framework
for organizing =d discussing the modeling state-of-the-artlpractice in Chapter 5. In addition, they
provide the basis for the development of model evaluation criteria, discussed in Section 4.4.
, c
The identified design issues have been grouped in Table 4.l into five categories: physical
system representation, representation of "active agents" in the system, representation of processes,
"generic" issues (which cut across virtually- all physical system, active agent and process
representation considerations)' and issues associated with the implementation of the model design
within an actual computational environment. The first three categories deal with the substance of
We system being modeled: the physical entities. Me behavioral entities, and the processes by which
these physical and behavioral entities evolve over time. The last two categories are more
methodological in nature. dealing with how the representation of these entities and processes is
actually implemented within an operational modeling system. Each of these groups of issues are
cliscussed in turn in the following sub-sections.
4.3.2 Physical System Representation
Fundamental to model design are decisions concerning the representation of the physical
elements of ~e system: time, land (space), buildings and transportation networks. These decisions
fundamentally affect the precision and accuracy of the models its data and computational
requirements, arid options for the representation of behavior within the physical urban system.
6 Note that these need not be the same thing! Theoretically crude approaches may well be very
computationally intensive, with all other combinations oftheoretical elegance and computational
requirements potentially existin, as well.
- :8
OCR for page 83
TChP H-17 Final Report
1 1
Table 4.l Integrated Urban Mode} Design Issues
Physical System Representation
O Time
O Space (land)
O Building stock
O Transportation networks
O Services
Representation of Decision Makers
O Persons
o Households
° Private firms
O Public authorities
Representation of Processes
o Land development
O Location choices
o Job market
O Demographics
O Regional economics
O Automobile holdings
o Activity/trave} demand
0 Network performance
"Generic Issues"
O Level of aggregation/disaggregation
0 Endogenous versus exogenous treatment
0 Level of "process type"
O Model specification
Implementation Issues
Dam requirements
Computational requirements
,9
OCR for page 106
TCRP H-12 Final Report
. . .
As currently envisioned, even an "ideal" mode] would probably have very limited
representation of these services. At a minimum a simple "serviced/not serviced" flax may well prove
adequate. The architecture of the mode] software, however. should be extensible to include a
broader arid more detailed representation of services as time. opportunity and need rams.
4.5.3.3 Representation of Decision-Makers
There are four fundamental decision-makers in urban areas: persons, households, private
ferns, and public authorities (government and other public agencies). All four tripes of decis~on-
makers must be explicitly represented in the model.
While there is obviously a strong "mapping" back and forth between persons and the
households within which they live, both representations are required within the model. Individuals
are born, age arid eventually die. They go to school work at jobs etc. Households. on the other
hand, are the appropriate decision-making units for residential location decisions automobile
transaction decisions, and for providing Me framework for understar~din~ the activity/travel patterns
of individual tr~p-makers.
Private florins provide the majority ofthe "economic energy" feeling urban processes. They
occupy land arid buildings, they demand and supply goods and services they employ workers. Trio
tripes of few which are of particular Interest within the model are developers (whose business it is
to develop land and construct buildings) and transportation firms (whose business it is to provide
transportation services to themselves and/or others).
Much of the behavior of public authorities lies outside the domain ofthe mode} per se in that
it represents the political and bureaucratic processes of public policy debate and decision-making,
the outcomes of which become exogenous inputs to the model. In addition however, public
authorities are typically major employers arid consumers (and providers) of land, floor space,
transportation and other goods and services within urban areas and so have endo~enous roles to play
within the mode] as well. Thus, it is import within the conceptualization of the model structure
to recognize the role of public authorities within urban areas, both as "exogenous drivers" of the
urban system, as well as endo~enous participants in the urban community's daily life.
Table 4.4 presents a representative list of possible attributes of persons. households, firms
and public authorities which might be included in an ideal model. In this table "utility" simply is
short-hand for whatever measures of person and household "satisfaction", "well-being", etc., are
being used within the mode] (discussed farther below).
- 82
OCR for page 107
TCRP H-12 Final Report
Table 4.4 Decision-Maker Attributes
~ : ~Actors i: Aft: ~ | ~ ::: : Attributes ~l
Persons ·Quality of life:
- utility being achieved
- travel {consistent with actrri~-based travels
· Work
. · Over
- place (location) utility
- other consumption / activity
- total utility': ~ Gavel, place. other utilities
· Age
· Sex
· Driver's licence
· Mobility restrictions
· Income Awake plus other; also taxes)
· Household role
· Employment (related attributes;:
- potential occupations
- current employment status:
- not in labor force
- unemployed
- employed:
-part time/fulltime
- occupation
- job location
- u age (and taxes)
· Education related attributes
- highest level of schooling attained
- current educational status:
- not a student
- part time / fills time
- level
- location
- 8:
OCR for page 108
TCRP H-12 Final Report
Table 4.4 Decision-Maker Attributes
i: Actors -I ~ : :- i: ~ : ~ Attributes : ~ ~ ~ :: ~ ~ ~: --it ~ :
.. .
Households · Dwelling unit
- location
- attributes
- property taxes
· Tenure
· Household utilities = ~ person utilities
·Vehicle availability
- number
-type
· Life cycle point of Be household (e.~., defined by number
of children etc.; will influence place / travel / other
utilities)
Private Establishment · Industry type
fi.e., a f rm, or a unit of · Finances
thatfirm, that has a - gross revenues
unique location. (NB: - gross costs (occupancy costs; including taxes,
carriers and developers especially property taxes)
fit within this framework, · Inputs
but are Two categories - capital
that have special roles / - number of jobs by occupation type
impacts in this model. - other roods and services (commodities, etc.)
Although these may be - space (location)
publicly-owned, they tend · Outputs (goods, services and infrastructure)
lo behave lilts private · Own-account shipping (yes / no):
establishments.)y - If yes:
- mode
- fleet size
Public Authorities fit e., · Industry type
according to unique · Finances
functional location) - revenues
- costs
· Inputs
- capital
- number jobs by occupation type
- other goods and services Commodities etc.)
- space (location)
· Outputs (goods, services and infrastructure)
· Own-account shipping (yes / no):
- If yes:
- mode
- fleet size
- 84
OCR for page 109
TCRP H-17 Final Report
-
In the market framework to be descnbed fur~er below, each of these four actors generally has
several roles; sometimes as a producer or supplier of goods and services, and sometimes as a
consumer or dem=der of these goods and services. For example, persons supply labor to firms, who
"consume" this labor. Retail fimns produce retail goods which are consumed by shoppers. Retailers,
in turret, are demanders of these same goods from wholesalers. And so on. Table 4.5 illustrates some
of the key production/consumption roles played by the four actor types with respect to key sectors
within the mode] (transportation, floor space and other goods and services).
4.~.3.4 Representation of Decision Processes
Market Processes. As outlined in Axioms 4 and i, a fundamental org~z~ng pnnciple for urban
areas is the market within which goods. services. =d money are exchanged between producers and
consumers. Prices for these goods and services are detennined through the market interaction; these
prices, In turn, determine the level arid nature of the exchanges Cat occur within the market between
supplier and demander.
Without explicit representation of the demand and supply processes at work within urban
markets-- and of the price signals which mediate between demand and supply -- it simply is
not possible to mode! adequately the outcomes from these markets.
Table 4.6 lists the key markets at work within urban systems along with the demanders and
suppliers in each case. As is clear Tom this table, market processes determine virtually every
element of interest within the land-use - transportation system, Including land development. location
choice processes, travel, and automobile ownership. As has already been discussed, individual
actors (persons, firms, etc.) participate in these markets in complex ways, sometimes as producers
and sometimes as consumers.
Development of an "ideal" model involves the explicit specification of demand and supply
processes for each of the markets listed in Table 4.6. While beyond the scope or capabilities of this
current study, this specification involves Get ring for each process the actorks) involved, the specific
decisions which they must make, the attributes of the actors which are salient to their decision-
making process, the attributes of the alternatives and the decision context which affect the decision,
and the "market clearing" mechanism by which demanders and suppliers interacts ultimately resulting
in the determination of prices and the exchange of goods and services. Central to the development
of these models is the issue of actor motivations, which is discussed briefly next.
- 8:
OCR for page 110
-
.
.
1: =,,: :
i, ~ ~ ! I
- := ~ 3~^
~1 - z~
r ~ ~ 1
:~ ~ _
~4'==
1
00
1
~4
~ .
.-
_
_ A,
_ _
O
,£4-
._ ~
A,,=
_
O
A_
~ C
._
~ it,
O ~
~ _
_
~ _
A, _
_
_
: ~ ~
?;~
hi.
_
o-
o
~ rat ~
_
O ._
~ _
_ ~
; rat
~ SAC
~ I_
O~
~ ~)
C ~
I. ~,
q~ ·_
_ ~
~ _
HE ~
OCR for page 111
TCRP H-12 Final Report
Table 4.6 Markets in the Urban System
.... -I . - ~ - . I. ~ ~ . . . . ; . .. . - ~ . .. ..
-:~: --Market :::- ~ :::: --I :- -:~::Demanders : :~ : -:: Suppliers
Housing Market Household Public authorities
Developers
Household
Floor Space Market ~Firms Developers
Public authorities Firms
Goods and Services ~ Persons Firms
Market (includes Households Public authorities
education) Firms
Public authorities
Job Market Firms Persons
Public authorities
Personal Transportation Persons Persons
Market Households
Firms
Public authorities
_
Goods Movement Market Persons Persons
Firms Households
Public authorities Firms (couriers etc.)
_
Inhas~ucture Market Persons Public authorities
Households Firms
Firms (couriers, etc.)
Public authorities
_
Auto (Vehicle) Market* Households Firms CAB: exogenous)
Firms
. Public authorities
* Interest is primarily in the personal vehicles.
Motivational Frameworks. In order to model actor decision processes in either a supply or a
demand context' one must have some understanding of the motivations driving the actor ~ question.
For persons and households, we believe it is reasonable to assume that this motivation is the
maximization of the "joint utility" of household members, subject to income, time and capability
constraints. At this level of the conceptualization, "utility" is used in a very loose sense of "well-
being" and does Ilot necessarily imply any particular modeling paradigm (e.g., random utility theory).
- 87
OCR for page 112
TCRP H-12 Final Report
-
Rather it simply represents the very basic assumption that we derive utilit~- fi:om (i.e.. we need)
. .. . .. ~ . . .. . . . . . . . . . . . .. ~ ~ . . .. .
sheller arid security tarlc so enter me nousm, market in order to obtain shelter). loon. clothing, etc.
(and so enter the retail market to obtain these goods), and so on. ~ order to obtain these things
within a market economy we need money, which we usually obtain by entering Me labor market and
selling our labor skills and knowledge for wages. Further, we need access to opportunities (jobs,
education, shopping, etc.) and so enter travel markets in order to gain physical access to the jobs,
schools, goods, services' etc. which we need and want. Thus. persons arid their associated
households enter various markets as demanders (housing, goods, services) or suppliers (labor. resale
housing): first, to achieve their basic needs, then to maximize their personal well-be~ng or utility.
Firms similarly can be assumed to be motivated by the desire to survive and prosper' where
"prospering" might be measured in a number of different ways (net revenue, reman on investment,
growth rate, etc.~. Regardless of the measurers) used, in order to survive, the fig must obtain
revenue from the production and sale of goods and/or services In response to either an existing
demand or anticipated (latent) demand; thus the final becomes active as a supplier in the market for
.. . . ~ . . .. . .. ~ . . . . . .
these goods or services. in order to Produce these goods the firm requires various inputs ( arid hence
is a demander of): labor, space, capital. and other physical Inputs. l he process of producing and
selling the goods/services also generates flows of goods tofDom the point of production. as well as
flows of business travel, thereby making the firm a demander (and sometime supplier) of
transportation services.
Finally, it is assumed that the motivation of public authorities is to maximize social welfare,
subject to societal budget, time and cacabili~v constraints. recoan~z~n~ that auantifvin~ this concept
. .. it, .. . ..
d. - 4 ~ ~ , _ ~
may be very o~cu~t In practice. In order to maximize (or at least to improve) social welfare, public
authorities often directly enter markets as suppliers of services and/or infrastructure, open in
situations in which private forms will not enter due to a perceived lack of profits.
In addition, public authorities seek to guide markets towards socially beneficial states through
a variety of policies, such as: provision of subsidies. taxation, income redis~bution~5 and regulation.
In order to accomplish these tasks, public authorities (just like private firms) enter markets to
demand labor, space, goods and services, and transportation.
Demographics. While implicitly shown as an exogenous "driver" of the urban system in Figure 4. I,
demographic processes are. in fact, an integral part of Me urban system and its internal dynamics.
Births, deaths aging, household formation/evolution/dissolution are fundamental processes
determining the characteristics of the population arid thereby the demand for housing, education,
jobs, goods and services, etc. Much of the explanatory power of disaggregate models of human
i5 This is somewhat redundant, since income redistribution is generally achieved through some combination
of subsidy and taxation. Subsidies and taxation, however, can be used for other purposes than income
redistribution (hence the distinction, for the purposes of this work).
- 88
OCR for page 113
TCRP H-19 Final Report
decision-making comes from being able to specify the atinbutes of the individuals involved, and
hence to be able to say something with reasonable confidence about their tastes and preferences, etc.
If such disaggregate decision models are to be employed effectively, then the overall modeling
system must be able to supply these decision models with the required decision-maker attributes.
As a result, a central and significant component of an ideal integrated modeling system is a strong,
endogenous, dynamic model of person and household demographics. This includes both the
capability to synthesize (if need be) the attributes of individuals and households in the base (initial)
system state, and to "update" or "evolve" these attributes over time within the overall simulation run.
Regional Economics. This relates to Me overall regional economic system within which individual
firms operate and compete, arid which determines the overall flow- of goods and services both
internally within the urban area and into/out of the urban area as import/export flows between the
urban area and the "outside world." Some regional economic factors/processes are exogenous to the
urban area and so to the model. such as interest rates, inflation, national immigration policy, and
perhaps total production levels by industrial sector. Other aspects are endogenous. In current
models, this component, if present, is usually handled through some form of input/output model, and
this is the most likely approach for models to maintain for some time to come.
4.5.4 Summary
Table 4.7 provides a brief summary of the attributes of the ideal integrated urban model
discussed above. These attributes are grouped according to the three main categories defined in
Table 4.1: physical system, decision makers and processes. Land development, location choice
processes, and job-worker linkages are all modeled as economic markets with explicit supply and
demand functions and procedures for price determination and "market clearing" (i.e., the allocation
of supply to demand). The model is envisioned to be dynamic, disaggregate and behaviorally sound.
As such, it will be sensitive to a wide range of land-use and transportation policies and able to trace
the direct arid indirect impacts of any of these policies through time and space.
No attempt has been made to specify; detailed formulations of individual sub-models within the
overall modeling system. Many options typically exist here, and much research is required in order
to translate this very general model into operational practice. Similarly, no attempt is made here to
address the data and computational requirements of such a model, except to note that such a
modeling system is almost certainly not beyond our current and emerging capabilities [Miller and
Salvini, 1998].
- 89
OCR for page 114
TCRP H-12 Final Report
Table 4.7 SuTr~nary of Ideal Integrated Mode! Attributes
PHYSICAL SYSTEM
Torte: Dynamic evolution of the system state In one-year time steps. System state generally
not in equilibrium. Interactions between long-run and short-run processes are ';properly"
accounted for.
Land: The basic unit of land is the individual lot.
Building Stock: Building stock is explicitly represented. Each lot has a certain amount of
floor space, characterized by type, price, etc.
Transportation Networks: Full, multimodal representation of the transportation system
used to move both people and goods. Sufficient spatial and temporal detail to properly mode!
flows, network performance, emissions, etc. Ideally, a twency-four hour network mode} to
be used.
Services: Sufficient representation of other services for the purpose of modeling land
development decisions.
DECISION MAKERS
Persons and Households: Both persons and households are explicitly maintained (with
appropriate "mappings" between the two entities) in sufficient detail to mode! the various
processes of interest.
Firms: Explicitly represented.
Firms at least as important as households in the overall
system: they occupy land / floor space; they employ workers; and they buy / sell goods and
services from / to themselves and households. Firms are modeled in sufficient detail to
capture adequately their behavior within these various roles.
Public Authorities:
Represented within the mode! to the extent they generate purely
endogenous effects (employers of workers, demander / supplier of services; etc.~. Will
remain represented largely by exogenous inputs to the model.
- 90
OCR for page 115
TChP H-12 Final Report
Table 4.7 Summary of Ideal Integrated Mode! Attributes, cont'd
PROCESSES
Markets: Land development, residential housing, commercial floor space and labor all
function within economic markets which possess demand and supply components and price
signals which mediate between demand and supply. These economic markets must be
explicitly modeled if them behavior over the is to be captured properly.
Demographics: Demographic processes should be modeled endogenously so as to ensure
that the distribution of population attributes (personal and household) are representative at
each point of time being modeled and are sufficiently detailed to support the behavioral
decision models being used.
Regional Economics: Essential components of urban production / consumption processes
should be modeled endogenously. The mode} should also be sensitive to macro exogenous
factors such as interest rates, national migration policies, etc.
Activity / Travel: The Gavel demand component of He integrated mode] should be activity-
based and sufficiently disaggre~ated so as to properly capture trip-makers' responses to a full
range of transportation policies, including ITS and TDM.
Automobile Holdings: Household auto holdings (number of vehicles, by type) should be
endogenously determined within the model.
91
OCR for page 116
TCRP H-12 Final Report
- 92
Representative terms from entire chapter:
public authorities
