where
£c=cost of travel by bus
£(c +2) =cost of travel by car
t=travel time by car (in minutes)
(t +10) =travel time by bus (in minutes)
We can now calculate the probability of the journey being made by car using
Equation 2.16:
So just over 80% of all trips made will be by car. If we assume that each car
has, on average, 1.2 occupants, multiplying each cell within Table 2.22 by 0.802
and dividing by 1.2 will deliver a final matrix of car trips between the seven
zones as shown in Table 2.23.
P
P
BUS UU
CAR UU
CAR BUS
BUS CAR
=∏ +()
=∏ +()
=
=∏ +()
=∏ +()
=
()-
()
()-
()-
11
11
0 198
11
11
0 802
14
14
e
e
e
e
.
.
.
.
Ucctt()CAR BUS- =-()-+()()- --+()()
=-+
=
25 00 06 2 001 10
25 12 01
14
....
...
.
Forecasting Future Traffic Flows 41
Destination zone
Origin zone A B C D E F G
A0 8213 1412 2241 1037 1190 614
B 1117 0 1203 3743 770 613 241
C 940 5895 0 2771 744 1022 327
D 422 5187 784 0 1820 1174 306
E 817 4461 880 7607 0 1578 2372
F 667 2529 860 3494 1123 0 3025
G 366 1056 292 968 1792 3213 0
Table 2.23Interzonal
trips by car
2.8.4 Trip assignment
The final stage involves assigning all the car trips in the matrix within Table 2.23
to the various links within the highway network shown in Fig. 2.3. Taking the
information on the interzonal travel times in Table 2.17 and using the ‘all-or-
nothing’ method of traffic assignment, the zone pairs contributing to the flow
along each link can be established (Table 2.24). The addition of the flows from
each pair along a given link allows its 2-way flow to be estimated. These are
shown in Fig. 2.4.
