1. Norman Washington Garrick CE 2710 Spring 2014 Lecture 07
Transportation Forecasting
Trip Generation
Norman Washington Garrick CE Spring Lecture 07

2. 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
Determines the specific route for each trip

3. 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 (TAZ) 1 2 3 4 5 6 8 7
The unit of analysis for traffic generation is the TAZ

4. Trip Generation Developing and Using the Model
Survey Base Year
Socio-economic, land use
and
Trip making
Calibrated
Model
Relating trip making
to socio-economic
and land use data
Estimated
Target year
socio-economic,
land use data
Predict
Target year
No. of Trips

5. Trip Generation Form of the Model
The trip generation model typically can take the form of
No. of trips = Function (population, income, auto ownership rates)
The model is developed and calibrated using the BASE year data

6. Trip Generation Travel Survey
Trip Generation models are often developed from travel surveys.
These surveys are used to determine the trip making pattern for a sampling of households in the area.
This trip making pattern is then related to land use and socioeconomic factors that are considered to affect travel patterns
Common socioeconomic factors considered include population, income, and auto ownership rates

7. 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
Recreational trips

8. Trip Generation Example of a Trip Generation Model
One way of presenting the trip generation model developed from a survey is as a cross-classification table

9. Trip Generation The Survey and The Model
Survey Base Year
Socio-economic, land use
And
Trip making
Calibrated
Model
Relating trip making
to socio-economic
and land use data

10. Trip Generation Trip Rates
Total Home-Based-Non-Work Trip Rates
Persons per Household
Type of Area
Vehicles per HH 1
2,3 4 5+
High Density 2+
Low Density

11. Trip Generation Trip Rates
Total Home-Based-Non-Work Trip Rates
Persons per Household
Type of Area
Vehicles per HH 1
2,3 4 5+
High Density
0.6
1.5 2+
1.8
Low Density

12. Trip Generation Trip Rates
Total Home-Based-Non-Work Trip Rates
Persons per Household
Type of Area
Vehicles per HH 1
2,3 4 5+
High Density
0.6
7.0
1.5
7.9 2+
1.8
8.3
Low Density

13. Trip Generation Trip Rates
Total Home-Based-Non-Work Trip Rates
Persons per Household
Type of Area
Vehicles per HH 1
2,3 4 5+
High Density
0.6
2.1
4.6
7.0
1.5
3.0
5.5
7.9 2+
1.8
3.4
5.9
8.3
Low Density

14. Trip Generation Trip Rates
Total Home-Based-Non-Work Trip Rates
Persons per Household
Type of Area
Vehicles per HH 1
2,3 4 5+
High Density
0.6
2.1
4.6
7.0
1.5
3.0
5.5
7.9 2+
1.8
3.4
5.9
8.3
Low Density
1.0
2.5
5.0
7.4
1.9
3.5
6.0
8.4
2.3
3.9
6.4
9.0

15. Trip Generation Estimating Target Year Data
Calibrated
Model
Relating trip making
to socio-economic
and land use data
Estimated
Target year
socio-economic,
land use data

16. Trip Generation Target Year Data
Number of Households in Target Year
Persons per Household
Type of Area
Vehicles per HH 1
2,3 4 5+
High Density 2+
Low Density

17. Trip Generation Target Year Data
Number of Households in Target Year
Persons per Household
Type of Area
Vehicles per HH 1
2,3 4 5+
High Density
100
200
300 2+
Low Density

18. Trip Generation Target Year Data
Number of Households in Target Year
Persons per Household
Type of Area
Vehicles per HH 1
2,3 4 5+
High Density
100
200
300 2+
Low Density 50 10

19. Trip Generation Predicting Number of Trips
Calibrated
Model
Relating trip making
to socio-economic
and land use data
Estimated
Target year
socio-economic,
land use data
Predict
Target year
No. of Trips

20. Trip Generation Predicting Number of Trips
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 2+
Low Density 60
Number of Trips = trip rate*no. of HH = 0.6 * 100 = 60

21. Trip Generation Predicting Number of Trips
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 60
420
460
700
300
900
1100
790 2+
180
680
590
1660
Low Density 50
250
500
740
190
600
840
230
390
640 90

22. Trip Generation Planning for the Future and Uncertainties
Earlier we talked 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
In considering the ‘trip generation’ process it is important to understand some potential sources of uncertainties

23. Trip Generation Sources of Uncertainties in Predicting Number of Trips
Significant errors can creep into the trip generation process in a number of places including
Errors in the survey
Who is surveyed, how well was the survey constructed, did we consider all important parameters?
Errors in the prediction of future demographics
Will the population grew, what will be the make up of the population
Errors in how well the model can actually reflect the future
Will the land use change, will transportation change, will technology change, will peoples attitudes change

24. Trip Generation Effect of Changes in Land Use
Changes in Land use and the type of transportation provided can have a huge impact on travel
But the trip generation process typically assume that this factor is constant over the period of the study

25. Trip Generation Demographics and Trip Making Factors affected by Land Use
The land use pattern and transportation type may affect
Car ownership rates
Household size and composition
Number of daily trips
Mode of trips
Length of trips