ANNEXURES
Annexure 1 - Transportation Modelling - An
Esoteric Exercise by W.R. Blunden....... 338
Annexure 2 - Cost-Benefit Analysis in the
Kyeemagh-Chullora Road Inquiry
by M.E. Beesley......................... 349
Annexure 3 - Discussion of the Economic
Analysis of Highway Improvements
by W.R. Blunden......................... 372
Annexure 1
- TRANSPORTATION MODELLING - AN ESOTERIC EXERCISE
BY W.R. BLUNDEN.
In the past two to three decades studies both on the
ground and theoretically of urban transport activity
have created a body of knowledge that provides the
transport planner with a number of useful laws and
formulae (generally these days cal1ed models) for
analysing and synthesising urban transport. However,
in his enthusiasm to apply them the planner lost sight
of his many limitations and as a result produced results
that are misleading and in many cases ridiculous even.
Further particularly in the urban situation, the
transportation sub-system to which they are applied is
only one half of the total land use,/transport system
which provides the minimal context in which urban
traffic activity can be defined. Although this
limitation is now widely appreciated, the standard urban
transport planning packages currently in use do not take
account of the land use factors except as exogenous input
variables. In major studies so much time and effort goes
into taking out one transport solution based on given land
use inputs that a re-run with a new land use input is
generally disregarded until a new "transportation study”
is commissioned.
transportation sub-system to which they are applied is
only one half of the total land use,/transport system
which provides the minimal context in which urban
traffic activity can be defined. Although this
limitation is now widely appreciated, the standard urban
transport planning packages currently in use do not take
account of the land use factors except as exogenous input
variables. In major studies so much time and effort goes
into taking out one transport solution based on given land
use inputs that a re-run with a new land use input is
generally disregarded until a new "transportation study”
is commissioned.
The major misconception on the application of transport
or land use/transport models is however the reliance
placed on them as predictors of the 20 year future. To
be useful as a rational analytical tool their role
be limited to one of analysis and synthesis.
or land use/transport models is however the reliance
placed on them as predictors of the 20 year future. To
be useful as a rational analytical tool their role
be limited to one of analysis and synthesis.
A Historical Backdrop
In the briefest terms the development of a professional
approach to transport planning may be outlined in the
following stages:-
1. in the late 30's and early 40's in the U.S.A. and
from the early 50's here the focus was on rural road transport problems and planning was based on
the extrapolation of historical growth trends of
measured traffic.
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2. when traffic engineers became concerned with
urban traffic in the late 50's and 60's the
growth of traffic on a given road had no real
significance for there were so many alternative
paths to take up increasing demand; also the
rapid growth of urban regions meant new roads
were needed where none had existed before and,
as a result, there was often no historical
traffic base for extrapolation. It was necessary
to determine a desire line pattern and hence the
trip table from more basic considerations. The
desire line pattern is based on land use activity
and, as a result, future traffic became directly
linked to growth in population and other socio-
economic activity. The Average Factor and Fratar
methods were much used up till the end of the 60's.
These methods produced a set of simple multipliers
for expanding currently measured traffic desire
lines based on the average predicted growth of the
trip ends at the land use zones at either end of
the desire line.
3. the new academic disciplines associated with
traffic phenomena have established a number of
basic propositions based on macro behaviour of
persons and goods movement, viz:-
(a) any land use generates traffic
in direct
proportion to its "size" or land use
potential.
proportion to its "size" or land use
potential.
(b) a relationship between land use
potential
and transport impedance (measured in terms
of distance, time, cost, or a combination)
determines a traffic demand pattern. This
relationship has a mathematical form very
similar to Newton's Law of Gravitation and
has become known as the gravity model.
and transport impedance (measured in terms
of distance, time, cost, or a combination)
determines a traffic demand pattern. This
relationship has a mathematical form very
similar to Newton's Law of Gravitation and
has become known as the gravity model.
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(c) a law that shows that when a
transport
demand is loaded onto a physical transport
element or system of elements the travel
time (or cost) will go up as the demand
increases slow1y up to about half the
capacity then as the capacity point is
reached very rapidly indeed. The rate of
demand in the steady state can’t exceed
the capacity of the transport element.
This law can be most usefully applied in
all kinds of traffic analysis but its most
important characteristic is that, taken
together with the inverse effect of travel
time in the gravity model, it guarantees
that the transport system will settle into
a state of equilibrium.
demand is loaded onto a physical transport
element or system of elements the travel
time (or cost) will go up as the demand
increases slow1y up to about half the
capacity then as the capacity point is
reached very rapidly indeed. The rate of
demand in the steady state can’t exceed
the capacity of the transport element.
This law can be most usefully applied in
all kinds of traffic analysis but its most
important characteristic is that, taken
together with the inverse effect of travel
time in the gravity model, it guarantees
that the transport system will settle into
a state of equilibrium.
(f) finally, it has been well
established, again
on a macro behavioural basis that other
things being equal travellers (or shippers)
will seek out the quickest (or cheapest)
combination of routes and modes for their
journey.
on a macro behavioural basis that other
things being equal travellers (or shippers)
will seek out the quickest (or cheapest)
combination of routes and modes for their
journey.
These three propositions provide the basic rationale
for what has become known as the 4-stage transportation
planning process or mode1. Starting with a given
system of land uses, trip productions and attractions
are calculated, the gravity model distributes them
between origins and destinations (i.e. gives trip
tables); this demand pattern is then split between
public and private transport facilities and, finally,
the car trips (i.e. private demand) are assigned to
road network.
for what has become known as the 4-stage transportation
planning process or mode1. Starting with a given
system of land uses, trip productions and attractions
are calculated, the gravity model distributes them
between origins and destinations (i.e. gives trip
tables); this demand pattern is then split between
public and private transport facilities and, finally,
the car trips (i.e. private demand) are assigned to
road network.
One should note here that this 4-stage transportation
planning model should not be confused with what is now
known as a four stage land use/transport model. In
this newer approach, which is generally regarded as
basic even though it has not as yet superseded the
transportation model in practice, the four stages are –
planning model should not be confused with what is now
known as a four stage land use/transport model. In
this newer approach, which is generally regarded as
basic even though it has not as yet superseded the
transportation model in practice, the four stages are –
- a land use model
- a generation model
- a distribution model
- an assignment model which incorporates
both modal split and road assignment.
The Use of Transportation (Land Use/Transportation)
Models
Models
The modelling procedure described above has been
extensively applied in urban transport planning
exercised to a virtually complete alphabet of cities
from the notable Chicago Area Transportation Study
(CATs) of the late 50's through to SATS (Sydney Area)
and has included BATS (Bay Area), MATS (Melbourne)
and many others. That the results have all been
generally disappointing has not been due to the
theoretical inadequacy of the modelling concepts but
rather to an unimaginative and stereotyped application
of them. Instead of using the model creatively to
compare the outcome of various future land use and
transport situations (scenarios) it has been “straight-
jacketed" with calibration coefficients based on
today’s traffic situation and then simply used for
empirical predictions into the 20 year future. In
fact, in spite of the elegance and conceptual
adequacy of the basic modelling rationale, the
transportation planner and analyst has never really
departed from the extrapolation art that was the
vogue before the modelling era.
extensively applied in urban transport planning
exercised to a virtually complete alphabet of cities
from the notable Chicago Area Transportation Study
(CATs) of the late 50's through to SATS (Sydney Area)
and has included BATS (Bay Area), MATS (Melbourne)
and many others. That the results have all been
generally disappointing has not been due to the
theoretical inadequacy of the modelling concepts but
rather to an unimaginative and stereotyped application
of them. Instead of using the model creatively to
compare the outcome of various future land use and
transport situations (scenarios) it has been “straight-
jacketed" with calibration coefficients based on
today’s traffic situation and then simply used for
empirical predictions into the 20 year future. In
fact, in spite of the elegance and conceptual
adequacy of the basic modelling rationale, the
transportation planner and analyst has never really
departed from the extrapolation art that was the
vogue before the modelling era.
It is absolutely vital to understand that the models
have no inherent prediction capability except perhaps
for the short term future. Even in this kind of
situation there are traps if genuine discontinuities
arise in respect of any of the important variables,
e.g. petrol availability, new norms for environmental
consequences and so on. Perhaps the most treacherous
aspect of the extrapolation process is the use of
"cross-section" regression to establish relationships
between certain variables notably between vehicle
ownership ratios and trip generation rates.
have no inherent prediction capability except perhaps
for the short term future. Even in this kind of
situation there are traps if genuine discontinuities
arise in respect of any of the important variables,
e.g. petrol availability, new norms for environmental
consequences and so on. Perhaps the most treacherous
aspect of the extrapolation process is the use of
"cross-section" regression to establish relationships
between certain variables notably between vehicle
ownership ratios and trip generation rates.
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Some Comments on the UTSG Evidence to the Commission
on the Use of Transportation Models for the Kyeemagh-
Chullora Road Options
The Urban Transport Study Group was established to
continue the work of the Sydney Area Transportation
Study and undertake new transportation studies for
Sydney and other areas of the State.
continue the work of the Sydney Area Transportation
Study and undertake new transportation studies for
Sydney and other areas of the State.
Its continuing work on the Sydney region is firmly
based methodologically on the models and techniques
of SATS and the passage of time has provided data
with which to test the SATS models and make further
adjustments to the many calibration factors which
they employ. Further, the continuing study allows
new theoretical developments to be incorporated, but
one must say in this regard that there is such a
deal of inertia inherent in the scale and elaboration
of the models and associated computer programs that
the impact of novelties is minimal.
based methodologically on the models and techniques
of SATS and the passage of time has provided data
with which to test the SATS models and make further
adjustments to the many calibration factors which
they employ. Further, the continuing study allows
new theoretical developments to be incorporated, but
one must say in this regard that there is such a
deal of inertia inherent in the scale and elaboration
of the models and associated computer programs that
the impact of novelties is minimal.
Perhaps the biggest dividend from the continuing study
and evaluation results from the feedback of criticism
and views of the various agencies and bodies,
particularly those concerned with the land use aspects
which are not modelled explicitly. This is, of course,
a slow process too. One might observe that something
of a breakthrough on this aspect may well result from
this Inquiry. I have referred often throughout the
seventies to a quotation from the Sharp Report -
Transport Planning - the Men for the Job. This report
was undertaken for the U.K. Minister of Transport and
published early in 1971:-
and evaluation results from the feedback of criticism
and views of the various agencies and bodies,
particularly those concerned with the land use aspects
which are not modelled explicitly. This is, of course,
a slow process too. One might observe that something
of a breakthrough on this aspect may well result from
this Inquiry. I have referred often throughout the
seventies to a quotation from the Sharp Report -
Transport Planning - the Men for the Job. This report
was undertaken for the U.K. Minister of Transport and
published early in 1971:-
"..strategic planning of land
use and
transport must be regarded as an integral
and continuous key function. The two
elements of the environmental planning
job cannot be tackled in isolation nor
merely by liaison between two separate
departments."
transport must be regarded as an integral
and continuous key function. The two
elements of the environmental planning
job cannot be tackled in isolation nor
merely by liaison between two separate
departments."
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The key recommendation arising from the report
states that a single committee and a single chief
officer be responsible for the whole of land use
planning and the whole of transport.
states that a single committee and a single chief
officer be responsible for the whole of land use
planning and the whole of transport.
With some perceptiveness of the practical problems
associated with this wide ranging field of activity
the report goes on: -
associated with this wide ranging field of activity
the report goes on: -
"This entails acceptance of
the inter-
changeability between those engaged in
land use planning and a loosening of
attitudes towards the question of
professional qualifications appropriate
to the whole field of planning...this
has got to come if planning is to be
properly served."
changeability between those engaged in
land use planning and a loosening of
attitudes towards the question of
professional qualifications appropriate
to the whole field of planning...this
has got to come if planning is to be
properly served."
It is my view that the Inquiry in bringing together
the separate departments and interests for open
discussion has gone a long way to recognising the
prognosis expressed by Lady Sharp
the separate departments and interests for open
discussion has gone a long way to recognising the
prognosis expressed by Lady Sharp
However, to revert to the current role of UTSG it
would be fair to say that it is a service agency
mainly to DMR, PEC, PTC - the three "executive"
agencies in the land use/transport scene. Even so
the jargon gap and the power of the computer tends to
confer an element of authority on the results produced
by UTSG.
would be fair to say that it is a service agency
mainly to DMR, PEC, PTC - the three "executive"
agencies in the land use/transport scene. Even so
the jargon gap and the power of the computer tends to
confer an element of authority on the results produced
by UTSG.
The evidence given by UTSG officers at hearings some
of which I have listened to and some I have studied in
the transcript has been most illuminating due largely
to the honest efforts of the witnesses to explain the
complex procedure of urban modelling and the relevance
and perspicuity of the questions put by the Commission.
Some observations follow.
of which I have listened to and some I have studied in
the transcript has been most illuminating due largely
to the honest efforts of the witnesses to explain the
complex procedure of urban modelling and the relevance
and perspicuity of the questions put by the Commission.
Some observations follow.
(a) The main thrust of the
examination was directed
towards the validity of the many assumptions
made in the modelling process, the authenticity
of the data base, the calibration procedures and
towards the validity of the many assumptions
made in the modelling process, the authenticity
of the data base, the calibration procedures and
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the accuracy of the final predictions. Generally
speaking, the defence put up by the witnesses
on all these matters was not convincing. This
was due to the point I have already made in my
general appraisal of the modelling process, i.e.
it has no inherent capability of making predic-
tions in real time. More specifically the
accuracy of the output is only as good as that
of the input or inputs. It was admitted many
times that in spite of the many factors included
in the model the primary ones were size and
distribution of the resident work force, the
numbers and distribution of the jobs and the
interzonal travel times (impedances). Because
the model itself does not incorporate a land
use phase, the first two main factors (i.e.
resident workers and jobs) were introduced as
inputs and needed to be independently extrapolated
to 1991. With 600 zones future estimates on a
zonal basis are very suspect. If a land use
model had been included, it would have been
necessary only to predict future population and
jobs for the whole metropolitan area. A general
"confession" on this basic matter seems to follow
Mr. Middleton’s question on Exhibit 43: Person
Trip Generation (Page 12 Day 3 of UTSG Appearance).
(b) I would repeat here that the
role of models is
for analyses and syntheses and not to provide an
elaborate surrogate for the crystal ball.
for analyses and syntheses and not to provide an
elaborate surrogate for the crystal ball.
(c) Another matter that confounds
and confuses much
of the discussion at the hearing is the "small”
zone syndrome. Transportation planners have
always been sensitive of missing short trips if
zones of interaction are made more realistic in
size, e.g. equal say to LGA's. But in relation
to major road systems does this really matter?
In my view it does not. Short trips are for all
practical purposes internal to reasonably sized
of the discussion at the hearing is the "small”
zone syndrome. Transportation planners have
always been sensitive of missing short trips if
zones of interaction are made more realistic in
size, e.g. equal say to LGA's. But in relation
to major road systems does this really matter?
In my view it does not. Short trips are for all
practical purposes internal to reasonably sized
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zones and are local in function -
school,
shopping. Certainly some local trips would
coincide with the peak period, but the most
part however the local trips have a different
time phasing to main inter-zonal work trips.
shopping. Certainly some local trips would
coincide with the peak period, but the most
part however the local trips have a different
time phasing to main inter-zonal work trips.
In my teaching I strongly recommend
that the
land/use transport model should be partitioned.
The principal metropolitan-wide land use and
transport interactions are reflected almost
wholly in the journey to (and from) work traffic
and in this context a duality exists between
land use and transport. In other words, it is
just as plausible that given a spread of job
locations a worker chooses his residential
location to "minimise" his journey to work as
it is that given an existing residential location
he will choose a job that is nearer rather than
further afield. This second proposition is
completely accepted by anyone ready to use the
gravity model - why not then accept the former.
land/use transport model should be partitioned.
The principal metropolitan-wide land use and
transport interactions are reflected almost
wholly in the journey to (and from) work traffic
and in this context a duality exists between
land use and transport. In other words, it is
just as plausible that given a spread of job
locations a worker chooses his residential
location to "minimise" his journey to work as
it is that given an existing residential location
he will choose a job that is nearer rather than
further afield. This second proposition is
completely accepted by anyone ready to use the
gravity model - why not then accept the former.
(d) The responses of the UTSG witnesses
to the further
explanation of matters relating to the model
"proper", i.e. the distribution modal split and
assignment of car traffic to the road network
does little to relieve one's concern as to the
meaningfulness of the 1991 estimates. The
distribution phase depends heavily on the transport
impedance which is quite sensitive to fuel costs
and perceived values of time; modal split is
strongly influenced by car ownership ratio and
personal preferences; assignment to the road
network is complicated by the many simplifications
that must of necessity be made to the real road
network, capacity considerations, definition of
the "peak" period and so on.
explanation of matters relating to the model
"proper", i.e. the distribution modal split and
assignment of car traffic to the road network
does little to relieve one's concern as to the
meaningfulness of the 1991 estimates. The
distribution phase depends heavily on the transport
impedance which is quite sensitive to fuel costs
and perceived values of time; modal split is
strongly influenced by car ownership ratio and
personal preferences; assignment to the road
network is complicated by the many simplifications
that must of necessity be made to the real road
network, capacity considerations, definition of
the "peak" period and so on.
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The reservations and criticisms of the modelling
process implicit in the above observations
undoubtedly raise doubts concerning its validity
as a planning tool. The main defence of the UTSG
witnesses in their defensive stance is that the
real worth of the process is based on relativities.
This is fair enough and one way of using models for
looking at the long term future is for carrying out
a sensitivity analysis. However, at this stage of
the professional application of modelling this is
not done in a frank and open manner.
An alternative approach implicit perhaps in the
rather dated 1st year benefits to capital cost ratio
as an index of merit is to focus attention of the
present. There are many traffic trouble spots in any
city that are currently identifiable. An analysis of
various methods of rectifying current deficiencies
would provide a much more realistic method of comparing
the costs and benefits involved. At the same time a
good understanding of the fundamental interactions
between land use and transport and amongst modes
implicit in the transportation modelling art together
with professional experience would provide a safeguard
against putting too many contemporary eggs in the one
basket.
rather dated 1st year benefits to capital cost ratio
as an index of merit is to focus attention of the
present. There are many traffic trouble spots in any
city that are currently identifiable. An analysis of
various methods of rectifying current deficiencies
would provide a much more realistic method of comparing
the costs and benefits involved. At the same time a
good understanding of the fundamental interactions
between land use and transport and amongst modes
implicit in the transportation modelling art together
with professional experience would provide a safeguard
against putting too many contemporary eggs in the one
basket.
Some Concluding Remarks on the Modelling Art
Although the basic philosophy and methodological
techniques of transportation modelling (better if it
were land use/transportation modelling) are both
conceptually adequate and potentially useful, their
application - in a detailed way to a system as vast
and complex as a large city has been far too ambitious.
As a consequence the results when critically examined
are generally disappointing.
techniques of transportation modelling (better if it
were land use/transportation modelling) are both
conceptually adequate and potentially useful, their
application - in a detailed way to a system as vast
and complex as a large city has been far too ambitious.
As a consequence the results when critically examined
are generally disappointing.
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The currently standard art is very well explained by
Brunton in his book to which reference has been made
by the Commissioner. I was surprised at the rather
disdainful rejoinder of the UTSG witness (when
admitting they had not heard of it) that if published
in 1972 it must be old hat and not worth serious
attention. I think it is a most useful book and
certainly encompasses the subject as comprehensively
as the current UTSG approach.
Brunton in his book to which reference has been made
by the Commissioner. I was surprised at the rather
disdainful rejoinder of the UTSG witness (when
admitting they had not heard of it) that if published
in 1972 it must be old hat and not worth serious
attention. I think it is a most useful book and
certainly encompasses the subject as comprehensively
as the current UTSG approach.
There are of course new approaches but they will need
the eighties for gestation. These approaches are
based on optimisation and more specifically are
directed at minimising energy consumption.
the eighties for gestation. These approaches are
based on optimisation and more specifically are
directed at minimising energy consumption.
It is perhaps interesting to summarise the history of
the art by decades, viz.
the art by decades, viz.
- the 50’s - traffic engineering aimed at
accommodating cars to the
exclusion of all other modes.
- 60’s - transportation planning recognising
other modes but mainly in a
lip-service way.
- 70's - land use and transport interaction
and the environmental consequences.
- 80’s - towards land use transport system
optimisation and minimisation of
energy consumption.
Although it is not appropriate to pursue a prognosis
of likely developments in the 80's, it is perhaps
worth mentioning that the techniques involved in
optimisation overcome many of the uncertainties of
open ended prediction methods.
of likely developments in the 80's, it is perhaps
worth mentioning that the techniques involved in
optimisation overcome many of the uncertainties of
open ended prediction methods.
- end of Annexure 1 -
