# Four Step Model - Transportation Engineering - Lecture Slides, Slides for Transportation Engineering. Allahabad University

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Some concept of Transportation Engineering are Basic Transportation Model, Classification of Urban Streets, Example of Shock Wave, Geometric Design of Highways, Route Choice, Trip Assignment, Time-Distance Diagrams. Main...
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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 step model’

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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

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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

8 7

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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

And Trip making

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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) The model is developed and calibrated using BASE year data

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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

Common socioeconomic factors considered include

population, income, and auto ownership rates

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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

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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

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Trip Generation Survey and Model

Calibrated Model

Relating trip making to socio-economic and land use data

Survey Base Year Socio-economic, land use

And Trip making

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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 9.0

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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

And Trip making

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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

1 100 200 100 100

2+ 100 100 100 10

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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

And Trip making

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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 1100 790

2+ 180 680 590 1660

Low Density 0 50 250 500 740

1 190 700 600 840

2+ 230 390 640 90

Number of Trips = trip rate*no. of HH = 0.6 * 100 = 60 Total trip = 13,080 Docsity.com

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

In considering the ‘trip generation’ process it is important

to understand some potential sources of uncertainties

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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 The use of the model for predicting the future

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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

relationship between the number of trips and the socio- economic factors.But the trip generation process typically assume that this relationship is constant over the period of the study

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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 Mode of trips Length of trips

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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 The two sets of terms sound similar but there is a technical difference

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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 Zone 1: 2 Trip Ends (1 O, 1 D) Zone 8: 2 Trip Ends (1 O, 1 D)

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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 Zone 1: 2 Trip Ends (2 Productions) Zone 8: 2 Trip Ends (2 Attractions)

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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 This is a useful distinction because of how trip generation models are

typically developed

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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

This approach works for home based trips (HB). But falls apart when we start to consider non-home based trips (NHB). Special techniques are developed to deal with the relatively small number of NHB that occurs.

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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

This method of trip generation is often used to do site impact studies

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