Basic Transportation Model - Transportation Engineering - Lecture Slides, Slides of Transportation Engineering

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The Four-Step Model

The Basic Transportation Model…

1) Study Area Zones

2) Attributes of Zones

 Socioeconomic Data

 Land Use Data

 “Cost” of Travel btw. Zones

3) The Road Network

 Traffic Volume by Road Link  Mode Splits  Emissions Inputs Outputs

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The Four-Step Modeling Process… I. Trip Generation II. Trip Distribution III. Mode Choice IV. Trip Assignment

Overview of the Four-Step Model

P/A versus O/D Trip Production Home end of the trip (where the need to make a trip is generated) Trip Attraction Non-home end of the trip (where the need to make a trip is satisfied) Trip Origin # of trips that begin in a zone Trip Destination # of trips the end in a zone

Zone 1 Residential Zone 2 Non-Residential

Zone 1 = Production & Origin

Zone 2 = Attraction

Destination

Zone 2 = Attraction & Origin

Zone 1 = Production

Destination

Some General Problems with the Conventional Methodology

• Pedestrians and bicyclists are rarely included - Level of geography is difficult for non-motorized modes - Network scale is insignificant - Input variables are too limited

Four-Step Model Problem

F Factor vs. Travel Time 0 10 20 30 40 50 60 70 80 90 0 2 4 6 8 10 Travel Time (min) F Factor 4 - Step Model Problem % of HH in Each Income Category Versus Auto Ownership Autos/HH 0 1 2+ Income Low 50 40 10 Medium 10 50 40 High 10 30 60 # of Trips per Household per Day Autos/HH 0 1 2+ Income Low 2 4 8 Medium 4 5 10 High 4 5 8 Trip Attraction Rates Attraction per per HH 1. Retail Employee 5. Non-Retail Employee 2. Travel Time Between Zones Zone 1 2 3 4 1 2 2 4 8 2 2 4 2 6 3 4 2 1 5 4 8 6 5 2 Alternative Modes vs. Density of Attraction Zone 0 5 10 15 20 25 30 35 40 45 0 200 400 600 800 1000 Household Density (HH / sq. mi.) of Attraction Zone % Walking & Biking

Basic Step-By-Step Process

• Trip Generation
  • Using the socioeconomic & land use data along with the cross-

classification tables, come up with the number of trip productions &

attractions for each zone…

• Trip Distribution
  • Create trip interchange table based upon “friction” between zones

using the travel time matrix, the F-Factor graph, and the Gravity

Model…

 Mode Choice

 Create a separate trip interchange table for each mode based upon, in

this case, the relationship of land use household density the

percentage of people walking & biking…

 Trip Assignment

 Distribute the vehicle trips to the street network using “all-or-

nothing” traffic assignment by assuming that all trips are

accommodated on the shortest possible path between zones…

Gravity Model T ij = P i A j Fij ΣA j Fij (Productions)(Attractions)(Friction Factor) Sum of the (Attractions x Friction Factors) of the Zones =

Travel Time = 2

1 3 4 2

Travel Time = 5 Travel Time = 6

Travel Time = 5

1 3 4 2