1. Fuzzy Dynamic Traffic Assignment Model
Transportation Program, CEE
Xuegang Ban
Dec. 14, 2001

2. Introduction to Traffic Assignment
Assign Traffic Flow to Links of The Network Given OD
Assumption: Each Driver Tries to Minimize His Perceived Travel Time
Characteristics:
- Stochastic and Dynamic
- Fuzziness of Driver’s Perception Over Travel Time

3. Fuzzy Sets of Perceived Link Travel Time
Deterministic Link Travel Time
Actual Link Travel Time
Fuzzy Sets of Perceived Link Travel Time
NORMAL
CONGESTED
INCIDENT
CONSTRUCTION
SPECIAL EVENTS
Membership Functions for Fuzzy Sets of Perceived Link Travel Time

4. Fuzzy Sets of Perceived Path Travel Time
Fuzzy Number Addition Problem
Dubois and Prade’s method
- Flattening, Decomposition, Operation * and Union
Fuzzy Addition Illustration

5. Fuzzy Assignment S: Set of Shortest Paths
Use Fuzzy Shortest Path Algorithm to Find S (Blue and Bush’s Method)
S: Set of Shortest Paths
Membership:
: Traffic Flow from Origin O to Destination D
: Traffic Flow in Path

6. Results Test Network: Link Properties: Link Number Start Node End Node
Length
(miles)
Capacity
(# of Vehi.)
# of Lane 1 3
2.5
2200 2 4 5 6 7 8

7. Results (Cont.) — Scenario #1
Link #
Flow from FDTA
Flow from SDTA
Flow difference(%)
>3
36.35
37.57
3.25
>4
38.65
37.43
3.26
>5
>5
>6
40.91
41.86
2.27
>7
34.09
33.14
2.87
>2
>2
All Links Are NORMAL
Both SDTA/FDTA Can Solve
This Problem
Difference Is Less Than 4%

8. Results (Cont.) – Scenario #2
Link #
Flow from FDTA
>3
24.64
>4
50.36
>5
>5
>6
52.18
>7
22.82
>2
>2
Link 1 and 6 Are CONGESTED
All Other Links Are NORMAL
FDTA Can Solve This Problem
SDTA Cannot.
Most of Drivers(70%) Will Choose
1->4->5->6->2(Link 2, 4, 5, 7)