1. Karen Tsang Bureau of Transport Statistics Department of Transport
Comparison of EMME Transit Assignment Methods Optimal Strategies vs Strategies with Variants (path assignment)
Karen Tsang Bureau of Transport Statistics
Department of Transport
May 2011

2. Overview A series of transit assignment experiments
◦ Compare standard and new methods
◦ To understand how flows are distributed
◦ Using simplified network (2 transit services)
◦ Variables : in-veh time, wait time, headway
choice between centroid connectors
Sydney Strategic Travel Model (STM) Network
◦ Rail Assignment Example

3. Standard vs New Current New Release Module 5.31 5.32 5.11 Option
Assignment Preparation
5.11
Option
One option:
1 = Optimal Strategies
* no path file
Two options:
* path file saved
* assignment results same as current
if additional gc and variants inputs
not specified
2 = Strategies with Variants
* distribute flows based on frequency
and transit time (optional)
* multiple paths at centroid connectors
(optional)

4. Standard vs New Current New Release STANDARD NEW Module 5.31 5.32 5.11
Assignment Preparation
5.11
Option
One option:
1 = Optimal Strategies
* no path file
Two options:
* path file saved
* assignment results same as current
if additional gc and variants inputs
not specified
2 = Strategies with Variants
* distribute flows based on frequency
and transit time (optional)
* multiple paths at centroid connectors
(optional)
STANDARD
NEW

5. Percentage of passengers using New service?
Experiment 1:
Demand from origin to destination = 100 passengers
No auxiliary (walk) link choice
New service variables
Headway: 5, 10, 15 and 20 minutes
Travel time: 1 to 40 minutes in 1 min interval
Percentage of passengers using New service?

6. Experiment 1: Assignment attributes and weighting factors:
In-vehicle time factor = 1.0
Auxiliary (walk) travel time factor = 2.0
Wait time factor = 2.0
Wait time = Headway/ 2
Boarding time = 5 min
Boarding time factor =1.0

7. Experiment 1: STANDARD Distribution of flows based on frequency NEW
based on frequency and transit time

8. Experiment 2: Reduced wait time weight
Wait time weight = 2.0 (Experiment 1)
Wait time weight = 1.0 (Experiment 2)

9. Experiment 2: Reduced wait time weight
STANDARD
Wait time weight = 1.0
STANDARD
Wait time weight = 2.0
Results from Experiment 1

10. Experiment 2: Reduced wait time weight
STANDARD
Wait time weight = 1.0
Flow distribution based on frequency
NEW
Wait time weight = 1.0
Flow distribution based on frequency and transit time

11. Experiment 3: Choice between connectors
Demand from origin to destination = 100 passengers
Choice between 2 centroid connectors
New service variables
Headway: 5, 10, 15 and 20 minutes
Travel time: 1 to 40 minutes in 1 min interval
Percentage of passengers using New service?

12. Experiment 3: Choice between connectors
STANDARD
One service route is chosen
All or nothing
NEW
Two centroid connector choices
Option 2 (logit)
Scale parameter = 0.2 (default)
where exp(-scale * transit time to destination)

13. Experiment 3: Choice between connectors
STANDARD
One service route is chosen
All or nothing
NEW
Two centroid connector choices
Option 2 (logit)
Scale parameter = 0.5
where exp(-scale * transit time to destination)

14. Experiment 3: Choice between connectors
STANDARD
One service route is chosen
All or nothing
NEW
Two centroid connector choices
Option 2 (logit)
Scale parameter = 0.8
where exp(-scale * transit time to destination)

15. Experiment 3: Choice between connectors
STANDARD
One service route is chosen
All or nothing
NEW
Two centroid connector choices
Option 2 (logit)
Scale parameter = 1.0
where exp(-scale * transit time to destination)

16. Key Differences Distribution of flows to attractive lines
Standard: based on frequency
New: based on frequency and transit time (optional)
Distribution of flows between connectors at centroids
Standard: one path with best generalised time (AON)
New: multiple paths at centroid connectors (optional)

17. Experiment Results Flow Distribution on attractive lines
Standard = Step function
New = Step with transition logit curve
Flow Distribution between multiple centroid connectors
Standard = AON
New = AON or multiple preferred paths

18. Sydney Strategic Travel Model (STM)
Rail Network
Rail Stations:
Over 340
Rail Transit Lines:
80 (approx)
Rail Link Length:
Approx 2400 km

19. Sydney Strategic Travel Model (STM)
Rail Line Example

20. Sydney Strategic Travel Model (STM)
Rail Lines (Entire Network)

21. STM Network - Rail Assignments
Fixed Demand: 3.5-hr rail AM demand
Network: Rail Network with walk and bus access/egress
Assignment Methods:
Travel zone to Travel zone assignments
Standard Assignment – Optimal Strategies
Strategies with Variants
– Path Saved
– Distribution of flows based on frequency and transit time
– Scale Parameter = 0.5

22. Rail Assigned Volumes
Method 1: Optimal strategies (standard)

23. Rail Assigned Volumes
Method 2: Strategies with variants (new)

24. Rail Assigned Volume Differences
Green =
Less volumes in new method
Red =
More volumes in new method
-6 %
+4 %
+1 %
+4 %

25. Conclusions: Rail Assignment
Rail assignment differences up to +/– 6%
Minimise back-tracking
Retain fast assignment run time
Standard = 1 minute, New = 2 minutes
Increase attractiveness of express services