MCRI Student Caucus Meeting
September 13, 2003
An Experimental Procedure for
Mid Block-Based Traffic Assignment
on Sub-area with Detailed Road Network
Tao Ye
M.A.Sc Candidate
University of Toronto
Outline
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Background and Problem Statement
Study Area and Data Resources
Procedure and Methodologies
Experimental Results
Summary and Conclusions
Background and Problem Statement
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Conventional zone-based model
Background and Problem Statement
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Conventional zone-based model
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Zone-based: centroid to centroid
Lack enough detail for intrazonal trips and short
trips (in GTA Model, 14% intrazonal trips are not
included in the traffic assignment model)
Only 40% of the real road network in the GTA is
included in the model
Not appropriate to provide accurate OriginDestination trip matrices for input into emerging
micro-simulation models of corridors or subnetworks
Objectives
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Develop an experimental procedure to implement
mid block-based (block: road link) traffic
assignment on a detailed sub-area network
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Create mid block points to realistically represent trip ends
Develop mid block-based trip matrix
Model the detailed network including all local streets
Perform mid block-based traffic assignment
Compare the results from mid block-based traffic
assignment and zone-based traffic assignment
Data processing and network modeling--ArcGIS8.2, Traffic assignment---EMME/2
Study Area --- Downtown Core (PD1)
Features (2001):
40.6 km2
64 traffic zones
86,900 households
164,200 residents
Data Resources
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From Data Management Group:
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2001 Transportation Tomorrow Survey (TTS)
2001 EMME/2 GTA network model
Traffic cordon counts in the study area
From Data, Map & Government Information Services:
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2001 Ontario detailed street map (Shapefile format)
2001 Ontario land use map (Shapefile format)
1996 Canada census: enumeration area (Shapefile format)
Building heights information from Statistics Canada (Shapefile)
2002 Toronto air photos linked from Toronto Public Library (Jpeg)
Procedure and Methodology
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Step 1: Create a traversal matrix for the study area from
the GTA model
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Step 2: Adjust the traversal OD matrix
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Step 3: Define mid block points
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Step 4: Estimate the production/attraction ratio for each
mid block point
Step 5: Redistribute zone-based trip matrix to mid blockbased trip matrix
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Step 6: Create sub-area detailed network model
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Step 7: Perform mid block-based traffic assignment
Create Traversal Matrix
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Traversal Matrix (as used in EMME/2): An O-D matrix for a
sub-area or a ramp-to-ramp matrix for a freeway facility
extracted from the total demand matrix
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Inputs:
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Identify and label all links entering and exiting from sub-area
Run a traversal matrix traffic assignment in EMME/2
Peak period auto-drive trip matrix retrieved from the 2001 TTS data
2001 EMME/2 GTA Network Model
Outputs:
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A sub area network extracted from the GTA network
An auto trip matrix consistent with the study area zone system,
considering all the GTA traffic flows
Traversal Matrix Adjustment
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Run the macro DEMADJ22 (a gradient approach) to get
the adjusted matrix
traffic count screeline
Define mid block points
•On
the main road
•Average
3-5 block
points for each zone
•Action
buffer
Distribution of mid block points
Estimate Production/Attraction Ratio
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Production ratio
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Based on the population size
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Census enumeration area population
Attraction Ratio
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Based on the floor space
Three land use categories: commercial, governmental and
institutional, industrial and storage
Assume 3-meter height as one floor layer
An example of the P/A ratio
Ratio in Traffic Zone
GTA2001_Zone Mid_Block_ID Production
Attraction
201
1001
0
0.4
201
1183
0.35
0.2
201
1184
0.15
0.2
201
1186
0.5
0.2
Generate mid block-based trip matrix
Tmn  Tij * Pmi * Anj
Where:
Tmn ----- Trips from mid block m to mid block n;
Tij ----- Trips from zone i (where m belongs to) to zone j (where n belongs to);
Pmi ----- Production ratio for mid block m within traffic zone i;
Anj ----- Attraction ratio for mid block n within traffic zone j.
Model a detailed network
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Mid block point
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Base network
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Obtain coordinates from ArcGIS
Assume features for local street links: lane number---1, free flow
speed---40, and lane capacity---400.
Turn tables
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DMTI format: from link to link
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EMME/2 format: from node to node
Experimental Results
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Comparison of two network model features
GTA Zone-based Model Mid Block Model
Internal Zones/Mid Block points 64
238
External zones
35
35
Regular nodes
286
1617
Directional links
1416
4476
Turn table entries
208
717
Experimental Results (cont’d)
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Mid block-based traffic assignment
Experimental Results (cont’d)
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Zone-based traffic assignment
Experimental Results (cont’d)
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Main road link volume analysis
Experimental Results (cont’d)
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Local street volume analysis
Experimental Results (cont’d)
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Running time analysis
Zone-based Assignment
Mid-block Assignment
Objective Function
ngap * =0.1
ngap=0.1
No. Of Iterations
11
16
Total CPU time (seconds)
5.3
33.8
*ngap: normalized gap, which is difference between
the mean trip time (or cost) at the previous iteration and the
mean minimal trip time (cost) computed by assigning the
demand to shortest path of the current iteration.
Conclusions and Recommendations
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Summary of benefits and values
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More realistic road network representation
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Suitable for data analysis of GPS-based personal travel surveys
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More precise results for traffic impact studies
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More accurate inputs for the traffic micro-simulation studies
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GTA model enhancement
Further research
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Combination of long trips and short trips --- windowed model
Consideration of other measures to estimate production and
attraction ratio
Enough traffic survey counts to conduct traversal matrix adjustment
Thank You!
Open for Questions...