FSUTMS Comprehensive Modeling Workshop - Cambridge ...

Overview – Equilibrium Assignment Process
Equilibrium Sample – 3 paths between zones A and B
FSUTMS--CUBE MODELING TRAINING SERIES
A
A
A
100
0
0
Iteration 0
0
100
0
25
75
0
Iteration 1
B
► First all-or
or-nothing assignment, all
100 trips from A to B are assigned
to the top path.
► The first iteration of capacity
restraint adjusts the link time on
that path based upon the BPR
curve and reloads the network,
again using an all-or
or-nothing
assignment. This results in 100
trips on the center path which is
now the minimum path.
► Program computes a combining
factor using a non-linear algorithm.
In this example the factor is 0.75,
or .75 x 100 to center path and .25
x 100 to top path.
7
Overview – Equilibrium Assignment Process
Equilibrium Sample (Cont'd)
A
0
0
100
B
A
19
58
23
B
Iteration 2
► Second iteration, again using an
all-or
or-nothing assignment, results
in 100 trips on the bottom path
which is now the minimum path.
► Program then computes a
combining factor using a non-linear
algorithm. In this example the
factor is 0.23, or 0.23 x 100 to
bottom path. This leaves 0.77 for
the other paths - 0.77 x 25 to the
top path and 0.77 x 75 to the
bottom path. Note that 19 + 58 +
23 = 100 trips.
FSUTMS--CUBE MODELING TRAINING SERIES
8
9-4