TRIP DISTRIBUTION
CHAPTER 8. TRIP DISTRIBUTION
NPTEL May 3, 2007
Chapter 8
Trip distribution
8.1
Overview
The decision to travel for a given purpose is called trip generation. These generated trips from each zone is then distributed to all other zones based on the choice of destination. This is called trip distribution which forms the second stage of travel demand modeling. There are a number of methods to distribute trips among destinations; and two such methods are growth factor model and gravity model. Growth factor model is a method which respond only to relative growth rates at origins and destinations and this is suitable for shortterm trend extrapolation. In gravity model, we start from assumptions about trip making behavior and the way it is influenced by external factors. An important aspect of the use of gravity models is their calibration, that is the task of fixing their parameters so that the base year travel pattern is well represented by the model.
8.2
8.2.1
Definitions and notations
Trip matrix
The trip pattern in a study area can be represented by means of a trip matrix or origin-destination (O-D)matrix.
This is a two dimensional array of cells where rows and columns represent each of the zones in the study area.
The notation of the trip matrix is given in figure 8:1.
The cells of each row i contain the trips originating in that zone which have as destinations the zones in the corresponding columns. Tij is the number of trips between origin i and destination j. Oi is the total number
Zones
1
2
.
.
.
.
.
. n Dj
1
T11
T21
2
T12
T22
...
...
...
j
T1j
T2j
...
...
...
n
T1n
T2n
...
Ti1
...
Ti2
...
...
...
Tij
...
...
...
Tin
...
Tni
D1
...
Tn2
D2
...
...
...
...
Tnj
Dj
...
...
...
...
Tnn
Dn
Oi
O1
O2
.
.
.
where Dj = Σi Tij , Oi = Σj Tij , and T = Σij Tij .
Oi
.
.
.
On
T
Figure 8:1: Notation of a trip matrix
Introduction
NPTEL May 3, 2007
Chapter 8
Trip distribution
8.1
Overview
The decision to travel for a given purpose is called trip generation. These generated trips from each zone is then distributed to all other zones based on the choice of destination. This is called trip distribution which forms the second stage of travel demand modeling. There are a number of methods to distribute trips among destinations; and two such methods are growth factor model and gravity model. Growth factor model is a method which respond only to relative growth rates at origins and destinations and this is suitable for shortterm trend extrapolation. In gravity model, we start from assumptions about trip making behavior and the way it is influenced by external factors. An important aspect of the use of gravity models is their calibration, that is the task of fixing their parameters so that the base year travel pattern is well represented by the model.
8.2
8.2.1
Definitions and notations
Trip matrix
The trip pattern in a study area can be represented by means of a trip matrix or origin-destination (O-D)matrix.
This is a two dimensional array of cells where rows and columns represent each of the zones in the study area.
The notation of the trip matrix is given in figure 8:1.
The cells of each row i contain the trips originating in that zone which have as destinations the zones in the corresponding columns. Tij is the number of trips between origin i and destination j. Oi is the total number
Zones
1
2
.
.
.
.
.
. n Dj
1
T11
T21
2
T12
T22
...
...
...
j
T1j
T2j
...
...
...
n
T1n
T2n
...
Ti1
...
Ti2
...
...
...
Tij
...
...
...
Tin
...
Tni
D1
...
Tn2
D2
...
...
...
...
Tnj
Dj
...
...
...
...
Tnn
Dn
Oi
O1
O2
.
.
.
where Dj = Σi Tij , Oi = Σj Tij , and T = Σij Tij .
Oi
.
.
.
On
T
Figure 8:1: Notation of a trip matrix
Introduction