Transportation Forecasting
What is it?
Transportation Forecasting is used to
estimate the number of travelers or
vehicles that will use a given
transportation facility in the future
The conventional approach to
transportation forecasting is based
on what is commonly know as the
‘four
The Four Step Model
• Trip Generation
Estimates the number of trips from given
origins and destinations
• Trip Distribution
Determines the destination for each trip
from a given origin
• Mode Choice
Determines the mode choice for each trip
• Route Assignment
Trip Generation
Trip Generation model is used to estimate the number of
person-trips that will begin or end in a given traffic analysis zone
The unit of analysis for traffic generation is the TAZ
1
2
3
4
5
6
Trip Generation
Developing and Using the Model
Calibrated
Model
Relating trip making to socio-economic
and land use data
Estimated
Target year
socio-economic,
land use data
Predicted
Target year
No. of Trips
Survey Base Year Socio-economic, land use
Trip Generation
Developing and Using the Model
The trip generation model typically can take the form of
No. of trips = Function (pop, income, auto ownership
rates)
Trip Generation
Developing the Model
Trip Generation models are often developed
from travel surveys. These surveys are
used to determine the trip making pattern
for a sampling of house holds in the area.
This trip making pattern is then related to
land use (nominally) and socioeconomic
factors that are considered to affect
travel patterns
Trip Generation
Trip Purpose
Often separate predictions are mode for different
type of trips since travel behavior depends on trip
purpose
In other words different models must be developed for
each trip type
The category of trip types commonly used include
• Work trips
• School trips
• Shopping trips
Trip Generation
Example of a Trip Generation Model
One way of presenting the trip generation
model developed from a survey is as a
Trip Generation
Survey and Model
Calibrated
Model
Relating trip making to socio-economic
and land use data Survey Base Year Socio-economic, land use
Trip Generation
Cross-classification Model
Total Home-Based-Non-Work Trip Rates
Persons per
Household
Type of
Area
Vehicles per
HH
1
2,3
4
5+
High
Density
0
0.6
2.1
4.6
7.
0
1
1.5
3.0
5.5
7.
9
2+
1.8
3.4
5.9
8.
3
Low
Density
0
1.0
2.5
5.0
7.
4
1
1.9
3.5
6.0
8.
4
2+
2.3
3.9
6.4
9.
Trip Generation
Developing and Using the Model
Calibrated
Model
Relating trip making to socio-economic
and land use data
Estimated
Target year
socio-economic,
land use data
Survey Base Year Socio-economic, land use
Trip Generation
Base Year Demographics
Number of Households in Target Year
Persons per
Household
Type of
Area
Vehicles per
HH
1
2,3
4
5+
High
Density
0
100
200
100
100
1
200
300
200
100
2+
100
200
100
200
Low
Density
0
50
100
100
100
Trip Generation
Developing and Using the Model
Calibrated
Model
Relating trip making to socio-economic
and land use data
Estimated
Target year
socio-economic,
land use data
Predicted
Target year
No. of Trips
Survey Base Year Socio-economic, land use
Norman W. Garrick
Trip Generation
Base Year Demographics
Number of Trips in Target Year for Each HH
Type
Persons per
Household
Type of
Area
Vehicles per
HH
1
2,3
4
5+
High
Density
0
60
420
460
700
1
300
900
110
0
790
2+
180
680
590
166
0
Low
Density
0
50
250
500
740
1
190
700
600
840
2+
230
390
640
90
Trip Generation
Planning for the Future and
Uncertainties
In an earlier lecture we talk about the
uncertainties associated with making prediction
for the future and the importance of not treating
predictions as if they are set in stone but rather
as a guide to help in decision making
Trip Generation
Sources of Uncertainties in
Predicting Number of Trips
Significant errors can creep into the trip
generation process in another of places
including
The model development
The Prediction of future demographics
Trip Generation
Modeling Land Use is one Major Source
of Uncertainty
•
The modeling of the different types of land use
and their effect on travel pattern is usually
relatively weak
•
Land use and transportation changes alter the
Trip Generation
Demographics and Trip Making Factors
affected by Land Use
The land use pattern may affect
Car ownership rates
Household size and composition
Number of daily trips
Trip Generation
What is Predicted?
Trip generation models predict so called TRIP ENDS
for each zone
The trip ends maybe classified as either
• ORIGINS and DESTINATIONS (O-D)
or
• PRODUCTIONS and ATTRACTIONS
Origins and Destinations
A worker leaves Zone 1 in the morning to go to work in Zone 8
This results in 2 trip ends:
• One Origin for Zone 1 • One Destination for Zone 8
1
8
Residential Non-residential
Residential
Non-residential
When that same worker leaves Zone 8 in the evening to go to home to Zone 1 This results in another 2 trip ends:
• One Destination for Zone 1 • One Origin for Zone 8
Total Number of Trip Ends
Productions and Attractions
A worker leaves Zone 1 in the morning to go to work in Zone 8
This results in 2 trip ends:
• One Production for Zone 1 • One Attraction for Zone 8
1
8
Residential Non-residential
Residential
Non-residential
When that same worker leaves Zone 8 in the evening to go to home to Zone 1 This results in another 2 trip ends:
• One Production for Zone 1 • One Attraction for Zone 8
Total Number of Trip Ends
Origins and Destinations??
Productions and Attractions??
Based on the convention of trip generation models
Origins
and
Destinations
are defined in terms of the direction of the trip
Productions
and
Attractions
are defined by the land use
Residential Land use
PRODUCES
trip ends
Non-residential land use
ATTRACTS
trip ends
Modeling Productions and
Attractions
Trip generation models typically model separately, i) residential trip production, ii)
non-residential trip attractions
1
Non-residential
Residential
For example, Trip Ends for Zone 1 would be
reported as
1.
1000 Production Trip Ends
2.
500 Attraction Trip Ends
Trip Rate Analysis Method of Trip
Generation
Trip-Rate Analysis
Trip rate is estimated on characteristics of the trip
generators with in the zone. Production rates are
determined using the characteristics of the residential
land uses and attraction rates using the characteristics of
the nonresidential land uses
Example
The characteristics of the trip generator is given in 1000 SQ. FT.
And the trip generation rate for each generator is given as TRIPS PER 1000 SQ. FT.
For example
Residential: Total 1000 Sq. Ft. = 2744 1000 sq. ft., Trip Gen. Rate = 2.4 trips/1000 sq.ft
TOTAL NO. of TRIP from residential land use = 2744*2.4 = 6586 Trips
