MODELLING NETWORKS FOR STRATEGIC AND TACTICAL PLANNING
A.M. Khan
Department of Civil and Environmental Engineering
Carleton University
Ottawa, Ontario K1S5B6
CANADA
Telephone: +613 520 2600 (EXT. 5786)
Fax: +613 520 3951
Email address: ata_khan@carleton.ca
S. Rathwell
Ottawa-Carleton Regional Transit Commission
Ottawa, Ontario K1G 0Z8
CANADA
Telephone: +613 842 3636 (EXT. 2414)
Fax: +613 230 6543
Email address: rathwells@octranspo.com
ABSTRACT
In urban transportation, three levels of planning activities are involved. These are
strategic, tactical and operational levels. This paper describes innovative application of
the EMME/2 for network modelling at the strategic and tactical planning levels for urban
transportation, with focus on public transit. Drawing upon research carried out at
Carleton University and Ottawa-Carleton Regional Public Transportation Commission
the paper provides information of interest to researchers as well as practitioners. The
paper advances ideas on the development and use of EMME/2-based strategic level (i.e.,
sketch) planning models.
PLANNING ISSUES
Urban transportation agencies are under much pressure to plan systems for private and
public transportation that cope with high demand for automobile travel and at the same
time increase or at least maintain transit ridership in a cost-effective manner in an
automobile-dominated society. Additionally, there are now new requirements to improve
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air quality and reduce greenhouse gas (GHG) emissions. While the planning tasks are
complex and challenging, the methods to be used have to be practical and feasible. For
many planning tasks, there is a lack of resources and time to produce very detailed
models. In such circumstances, new innovative approaches are required.
NETWORK PLANNING
In an urban transportation organization, planning is carried out at three levels;
. Strategic Level
. Tactical Level
. Operational Level
The strategic level is policy driven and works at an aggregated level of analysis. The
policies that are normally implemented are aimed at the balance of transportation and
land use on one hand and, on the other hand the balance of private and public
transportation. In an urban public transit organization, the strategic level planning efforts
are of broader nature and are generally intended for relatively long periods (Figure 1).
Strategic Level Planning Examples
Overall Urban Transportation Systems
. Integrated land use – transportation system planning
. Application of demand or supply measures for congestion relief
Examples: introduction of high occupancy vehicle (HOV) lanes;
Public transit improvements
Public Transit System Planning
. Corridor and service concepts
. Infrastructure planning
. Workforce planning
. Equipment planning
Figure 1: Strategic Level Planning
For urban public transit, typical strategic planning studies include system modelling for
testing alternative transit service strategies and determining human, capital and physical
resource requirements. At this level, the details of service and other plans are not
available. However, there is the opportunity to receive feedback from the relatively more
detailed tactical studies, which deal with medium to short term levels of planning
problems.
The tactical level planning in urban transportation works within the framework provided
by strategic planning. At this level, analyses are relatively more detailed than at the
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strategic level. At the tactical level, the transportation system must be studied at a much
greater level of detail than at the strategic level (i.e. lane configurations, traffic signal
settings) (Figure 2).
Tactical Level Planning Examples
Overall Urban Transportation System
. Traffic management schemes based on pricing and technology innovations.
. Applications of the Intelligent Transportation Systems are prime candidates.
Public Transit System
. Route planning and scheduling
- Workforce
- Equipment
- Assignment of traffic to infrastructure
Figure 2: Tactical Level Planning
Operational Level Planning Examples
Overall Urban Transportation Systems
. Advanced traffic management & control system operations; dynamic parking.
Public Transit System
. Detailed assignments within a day
. Passenger counts
. Vehicle control
. Public information
. Maintenance schedule
Figure 3: Operational Level Planning
At the operational level, actual dynamics of urban traffic management (i.e., travelles,
vehicles and control systems) are studied. In an urban transit organization, the operational
level studies cover activities that are carried out during various times within a day
(Figure 3).
SYSTEM MODELLING WITH EMME/2
The EMME/2 is widely used in Canada (and elsewhere around the world) mainly for
tactical level detailed planning work since it is among the most sophisticated packages in
terms of its flexibility and comprehensiveness. There appears to be a need to develop
EMME/2 modelling framework to test in an expedient fashion the answers to questions
that are of strategic nature. Selected examples include:
. Congestion reduction with transportation policy measures.
. Travel demand implications of land use changes.
. The effectiveness of improvements in public transit in reducing GHG emissions.
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In the case of public transit, EMME/2 is widely used at the tactical level. For effective
application at the strategic level, an interactive planning model has to be developed that is
coarser than the detailed tactical model. Such a model can be less demanding in terms of
input data required and takes fewer resources including time than the detailed model.
Additionally, this paper highlights that the results obtained from such a model are also
satisfactory for strategic level planning.
INTERACTIVE PLANNING MODEL
The EMME/2 modelling framework can be used at the strategic and tactical levels for
testing service strategies and estimating resource requirements. The utility of this model
is particularly well pronounced for tactical level studies. The model has to be calibrated
for simulating the public transportation system. Once calibrated , the model enables the
identification of system improvements, testing effects on passenger service, and
estimation of operational costs.
Among many interactive uses of the model is the identification of the lowest cost route.
The model can be used for the simulation of existing or proposed networks. Long range
or strategic planning (e.g., travel growth scenarios) could be handled as well. For some
strategic planning tasks, but specifically for tactical studies, the EMME/2 is used.
At a very detailed level, this model accurately simulates a public transit system, enabling
the identification and testing of potential areas for improving the system as well as
determining the resulting effects on passengers and operational costs. As a zonally based
aggregate demand model, it is capable of generating auto, transit, or combined bimodal
travel assignments. The demand input for the model is a matrix of zonally aggregated
origin-destination trips. The supply component of the model is formed by the base
network and transit lines (Figure 4).
As is clear from Figure 4, networks, matrices, and functions make up the core of the
database, and other data such as demarcation lines are included as auxiliary data. The
interactive model finds the lowest cost route by starting at a given destination and
working backwards to all origins.
The algorithm can handle route choice decisions that involve a high frequency of route
and transfer, as well as low frequency but direct routes. This model allows these choices
to be combined. The algorithm compares the in-vehicle time, walking (auxiliary transit)
time, waiting time, and boarding time components of different trip options and selects the
result that minimizes the total perceived origin to destination journey time.
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Network for Various Scenarios
. Modes. Demand
. Base network. Socio-economic factors
. Turn penalties. Etc.
. Transit vehicles
. Transit lines
Matrices (by O-D)
Functions
. Volume-delay
Auxiliary Data. Demand
. Turn penalty
.Transit time
. User defined
Network Structure
. Nodes, centroids
. Links
. Turns
. Modes
. Transit vehicles
. Transit lines
Figure 4: EMME/2 Data Base & Network Structure: Detailed Interactive Planning
Model
The detailed interactive model used at the OC Transpo is an aggregate demand model
consisting of all region level travel zones superimposed upon a digitized map of
approximately 5700 links, 1300 nodes, and 160 transit lines. The model can be used for:
the simulation of the existing network, the study of proposed route and network
alternations, and the development of long range planning capabilities. However, for the
application of a basically tactical level planning model to strategic planning questions, a
significant amount of time is required to prepare the network.
This paper focuses on the development and testing of a new EMME/2-based strategic
level (i.e., sketch) planning (1,2,3,4). This was a challenging task, given the requirement
to produce reasonably accurate results with relatively aggregate level inputs such as
service and network definitions.
SKETCH PLANNING MODEL
The development and testing of a new strategic level (i.e., sketch) planning model is a
challenging task, given the requirement to produce reasonably accurate results with
relatively aggregate level inputs such as service and network definitions. In this research,
it was decided to modify the detailed model structure, calibrate the model by using
specifically prepared aggregate level inputs, and test the model in the form of some
planning applications. Results were compared with the detailed model.
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The steps necessary for the development of sketch planning model were:
1. adopting the logic structure of the detailed tactical level planning model,
2. zone grouping,
3. network aggregation, and
4. model calibration
There was no need to introduce new theoretical frameworks for the development of the
sketch planning model. The theoretical base of the EMME/2 applies to the detailed as
well as the sketch planning model. The knowledge of the EMME/2 system logic was
used in an innovative manner for the tailoring of the sketch planning model.
In the detailed assignment model, the optimum travel time can potentially be calculated
for every origin-destination pair in the travel demand matrix. For the entire region zonal
system that has to be coded in the OC Transpo’s detailed model, this could mean
numerous inputs and coding operations. Any reduction in the number of zones results in a
significant reduction of inputs and coding activities.
For the sketch planning model, the number of zones was reduced to about one-third
directly compatible zones. The new, larger zones correspond directly to the zones used by
the regional Municipality of Ottawa-Carleton in the multimodal aggregate transportation
mode. The travel demand matrix was compressed as well through zone grouping.
For zone reduction, zone centroids in the detailed model had to be replaced with new
centroids corresponding to larger zones. The centroid replacement activity was carried
out using the EMME/2 system’s interactive graphic capability.
The detailed network consists of links and nodes that sometimes are not used by public
transit services. Their presence is justified on the basis of completeness and ease of
understanding graphic output from the EMME/2 system. For the sketch planning model,
the unnecessary links and nodes were deleted by using the EMME/2 in an interactive
graphical mode.
A number of benefits are gained by deleting the unnecessary nodes and links. First, the
size of the network is reduced by 31%. This allowed the potential size of the EMME/2
data base to be reduced, thus resulting in saving of time and resources to update and
maintain the database. Additionally, such a coarser simpler network offers the ease of
answering “what-if” type of questions of strategic nature.
The simplification of the transit line was a challenging task. It required a great deal of
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creativity to successfully aggregate a set of detailed transit lines into a smaller more
abstract but comparable set of detailed transit lines. This task was carried out in two
stages.
First, those transit lines were identified and combined that provided similar services. For
example, two lines with the same start and end nodes but operated in neighbourhoods on
opposite sides of a major roadway were consolidated and the new route was shown on the
roadway between the neighbourhoods. Additionally, at this stage, different service
patterns of the same transit line were combined into a single line without sacrificing the
essential characteristics.
At the second stage, the location and of the new zones and their connection to the
simplified base network was studied with the objective of finding a simple yet accurate
collection of transit lines for serving new zones. The procedure followed called for: (a)
the identification of existing transit lines that could be aggregated while still delivering
the required service to the communities they served, and (b) the creation of new lines that
could replace two or more existing lines while delivering effectively the same service.
The result of the two-stage process was a modified aggregate level transit network. The
The interactive graphical capabilities of the EMME/2 system was used in association
with the regular VAX VMS editing capabilities for the implementation of changes. The
process of simplifying the transit lines reduced the number of lines by about 52%.
The calibration of the sketch-planning model required essentially the same steps as the
detailed model. The difference was in the format of the observed boarding from the
survey data. The observed boardings on existing routes had to be combined in the same
manner as the original transit lines had been aggregated. During the calibration process,
accuracy checks were made. Logically, the guidelines followed for the calibration of the
detailed model were found to be applicable to the sketch-planning model.
CASE STUDIES
A number of innovative applications of the models were carried out. Travel assignments
carried out using the detailed model as well as the sketch planning model resulted in a
variety of general information that is useful in providing an overall picture of the
assignment. See Table 1
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Table 1: Comparison of Results
Factor
Total demand
Assigned demand
Total boardings
Passenger kms
Passenger hours
Avg. load factor
Transfer rate
Average trip length (km)
Avg. in-vehicle time (min)
Speed made good (km/h)
Percent Difference Between
Detailed and Sketch Planning Models
Identical demand
-1.6%
+2.4%
-1.3%
-3.6%
+5.3%
+5.0%
+3.0%
-2.0%
-0.3%
As expected, the data provided in Table 1 show that the sketch planning model caused
some loss of accuracy compared with the detailed model. Two other areas for comparison
between the two models, although not tabulated here, are the transit line boardings and
transfer boardings. In both cases, the level of detail produced by sketch planning model
was somewhat reduced as compared to the tactical model.
In order to further assess the usefulness of the sketch planning model, two appropriate
planning exercises were developed and analyzed using both the detailed model and the
sketch planning mode. The first case study involved the elimination of express route 74
and an analysis of how ridership changed on routes 72, 172, and 174, the other routes in
the area, as a result. Summary of results are shown in Table 2.
Table 2: Case Study Results
Percent Difference Between
Detailed Model and Sketch Planning Model
Case 1:
Peak –hour Boarding With Route 74
Peak-hour Boarding Without Route 74
-3.1%
-2.3%
Case 2:
Peak-hour Boardings Before
Population Increase
Peak-hour Boardings After
Population Increase
+3.1%
+2.8%
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The second case study required that the population, and as a result, transit ridership, be
increased, in one zone owing to new residential development. The models were used to
determine where increased service might be required. As expected, the detailed model
showed that increased service would be required on two specific express routes, whereas
the sketch planning model showed that “more service would be needed in the east end”
without being specific about route(s).
CONCLUSIONS
1. At the three levels of planning, namely the strategic, tactical and operational levels,
computer models are essential for service and other planning functions, especially
under resource constraints.
2. Given the need for efficient provision of urban transit services under resource
constraints, especially in developing countries, experience with computer-based
systems described in this paper should be of interest to the transportation profession.
3. Models required have to be tailored for each level of planning problem. Although the
prototype sketch planning model does not show major loss of accuracy, further
development work would be required for producing a more appropriate (efficient)
sketch planning model for use at the strategic planning level.
4. The model structure can be tailored to suit the requirements for each level of planning
problems. The sketch planning model for use at the strategic level shows promise.
Given that preparation time is an issue, the sketch planning model allows for quick
preparation to answer strategic level questions without getting bogged down in the
detail of a full model run.
ACKNOWLEDGEMENTS
The views expressed are those of the authors. The use of OC Transpo’s data and
computer modelling system are gratefully acknowledged. Financial support from the
Natural Sciences and Engineering Research Council (NSERC) is acknowledged.
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REFERENCES
1. INRO, “EMME/2 User’s Manual”, Montreal 1998.
2. Sean H. Rathwell, “Development of An EMME/2 Sketch Planning Model at OC
Transpo”, M. Eng. Project, Carleton University, 1987.
3. Sean H. Rathwell, Ata Khan, and William F. Johnson, “Application of Advanced
Planning Models for Efficient Public Transportation”, International Conference,
Institute Des Sciences Et Des Techniques De Léquipment Et De L’Environment Pour
Le Development”, International Conference, Urban Management and Development,
20-22 September 1988, Lyon, France.
4. Ata M. Khan and Sean H. Rathwell, “Advanced Computer-Based Systems for
Efficient Urban Public Transportation”, IV-ICCCBE ’91 Conference, Tokyo, 1991.
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