TRANSPORTATION MODELING

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TRANSPORTATIONMODELING


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QUOTABLEQUOTES

"After I'm dead I'd rather have people ask why I

have no monument than why I have one.- Cato the Elder

(234-149 BC, AKA Marcus Porcius Cato)


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TRANSPORTATION MODELING

Transportation Modeling orTransportation Forecasting isthe process of estimating the number of vehicles orpeople that will use a specific transportation facility in thefuture. For instance, a forecast may estimate;

a) number of vehicles on a planned road or bridge

b) ridership on a railway line

c) number of passengers visiting an airport

d) number of ships calling on a seaport

What does itmean?


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Traffic forecasting begins with the collection of data oncurrent traffic. This traffic data is combined with otherknown data, such as population, employment, trip rates,travel costs, etc., to develop a traffic demand model for

the current situation.

Feeding it with predicted data for population,employment, etc. results in estimates of future traffic,typically estimated for each segment of thetransportation infrastructure in question, e.g., for each

roadway segment or railway station.

How is itdone?


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Traffic forecasts are used for several key purposes intransportation policy, planning, and engineering:

a) to calculate the capacity of infrastructure, e.g.,how many lanes a bridge should have;

b) to estimate the financial and social viability ofprojects, e.g., using cost-benefit analysis andsocial impact assessment; and

c) to calculate environmental impacts, e.g., airpollution and noise

Why is itimportant?


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Within the rational planning framework,transportation forecasts have traditionallyfollowed the sequential four-step model or

Urban Transportation Planning (UTP) procedure,first implemented on mainframe computers inthe 1950s at the Detroit Area TransportationStudy and Chicago Area Transportation Study(CATS).

Four-step Model


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Trip Generation. Determines the frequencyof origins or destinations of trips in each zone by

trip purpose, as a function of land uses andhousehold demographics, and other socio-

economic factors.

Four-step Model: The 1st Step


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Trip Distribution. Determines the originor destination of trips that are generated at a

given activity.

Four-step Model: The 2nd Step


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Modal Split. Determines which mode oftransportation will be used to make the trip.

Four-step Model: The 3rd Step


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Traffic Assignment. Determines whichroute on the transportation network will be

used when making the trip.

Four-step Model: The 4th Step


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Four-step Model: Diagram


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Procedural Summary

1

Data collection (population, land use,

etc.)

2

Analysis of existing conditions andcalibration

3

Forecast of future travel demand (the

Four-step Model)

4 Analysis of the results


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a) for nine out of ten railway projects the studyfound that passenger forecasts wereoverestimated, with an average overestimate of106%

b) for half (50%+) of all road projects, includingbridges and tunnels, the study found that thedifference between actual and forecast trafficwas more than 20%, while for 25% of road

projects the difference was more than 40%

InaccuracyIssues?!

-Flyvbjerg, Holm, and Buhl (January 2006). "Inaccuracy in Traffic

Forecasts". Vol. 26, No. 1, 124. Transport Reviews.


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FUN FACTS & TRIVIAS

Longest Bridge? The DanyangKunshan

Grand Bridge, in China, is the world's

longest bridge. It is a 164.8 kilometers

(102.4 mi) long.

Widest Highway? With 26 lanes in certain parts,

the Katy Freeway or Interstate 10, in USA, is the

widest highway in the world. It serves more than

219,000 vehicles daily in Texas.


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The EndProDeo, Familiaet Patria

TRANSPORTATION MODELING

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