lec 14 demand forecasting 2008 ( transportation engineering dr.lina shbeeb )

Transportation Engineering

Transportation Planning Process

Transportation Planning

What are some examples of goals and

objectives for a transportation system?

Forecasting Travel

How do we know what travel behavior

will be like in 20 years?

Defining Study Area Delineate boundaries and subdivide into zones

Zones Should Have Following Characteristics

Homogeneous Socioeconomic Characteristics

Intrazonal Trips Should Be Minimized

Use Physical, Political, and Historical Boundaries if Possible

Zones Should Not Be Created Within Other Zones

The Zone System Should Generate and Attract Approximately Equal

Trips, Households, Population,or Area

Use Census Tract Boundaries Where Possible.

Example for TAZs

Forecasting Travel

Population and Economic Data

Transportation Inventories

Travel Surveys

Forecasting Travel

Calibration

Establishing a mathematical relationship to estimate future

travel demand

Trip Estimation Example A multiple regression analysis shows the following

relationship for the number of trips per household: T = 0.82 + 1.3P + 2.1A

T = Trips per household per day

P = persons per household

A = Autos per household

Zone contains 250 households with an average of 4 persons and 2 autos for each household, determine the average number of trips per day in that zone .


Environmental Impact Statements

Purpose and Need

Alternatives

Environmental Effects

Highway Engineering

Forecasting Travel Demand

Growth Rate Methods (Rural)

Urban and Intercity Travel Forecasting


Factors Influencing Travel Demand

Location and intensity of land use

Socioeconomic Characteristics of the

population

Extent, Cost, and Quality of the available

transportation


What are some factors that affect

how much you travel?


Trip generation

Process for determining the number of trips that will begin and

end in each traffic zone.

Trip Generation

Trip End

Trip Production

Trip Attraction

Trip Generation

Classification of Trips

Home-Based Work (HBW)

Home-Based Other (HBO)

Non Home Based (NHB)

Trip Generation

Two functions of trip generation

Develop a relationship between trip end production or

attraction and land use

Use the relationship developed to estimate the number of trips

generated at some future date under a new set of land-use

conditions

Trip Generation

Cross classification method of trip

generation

Develop relationship between socioeconomic

measures and trip generation

Trip Generation Example

Develop a set of curves showing the number of trips per

household versus income and auto ownership.

Trip Generation Example Household # Trips Produced Income ($1000) Autos

1 2 16 0 2 4 24 0 3 10 68 2 4 5 44 0 5 5 18 1 6 15 68 3 7 7 38 1 8 4 36 0 9 6 28 1

10 13 76 3 11 8 72 1 12 6 32 1 13 9 28 2 14 11 44 2 15 10 44 2 16 11 52 2 17 12 60 2 18 8 44 1 19 8 52 1 20 6 28 1


Income ($1000)

Autos Owned Total

0 1 2+

24 2 (67) 1 (33) 0 (0) 3 (100)

24 – 36 1 (20) 3 (60) 1 (20) 5 (100)

36 – 48 1 (20) 2 (40) 2 (40) 5 (100)

48 – 60 0 (0) 1 (33) 2 (67) 3 (100)

> 60 0 (0) 1 (25) 3 (75) 4 (100)

Total 4 8 8 20

Number & Percent of Household in Each Income Category Versus Car Ownership


Income ($1000)

Autos Owned

0 1 2 +

<24 3 5 --

24 – 36 4 6 9

36 – 48 5 7.5 10.5

48 – 60 -- 8.5 11.5

>60 -- 8.5 12.7

Average Trips per Household Versus Income and Car Ownership


Trips per Household per Day by Auto Ownership and Income Category


Trips by Purpose and Income Category


Determine the number of trips per day generated for each

trip purpose.

Number of dwelling units: 60

Average income per dwelling unit: $44,000

Income ($) Households

Low (under 32,000) 9

Medium (32,000 – 48,000) 40

High (over 48,000) 51


Income Cars / Household

0 1 2 +

Low 54 42 4

Medium 4 58 38

High 2 30 68

Percentage of Households in Each Income Category Versus Auto Ownership


Income Autos / Household

0 1 2 +

Low 1 6 7

Medium 2 8 13

High 3 11 15

Number of Trips per Household per Day


Pgh = number of trips per day generated by householders with income level g and auto ownership h

HH = number of households

Ig = Percentage of households with income level g

Agh = Percentage of household in income level g with h autos per household

(PH)gh = Number of trips per day produced in household at income level g and auto ownership h

Pgh=HH X Ig X Agh X (PH)gh


Income, # of Autos Trips Total by Group

L, 0 3

19 L, 1 14

L, 2+ 2

M, 0 2

232 M, 1 111

M, 2+ 119

H, 0 2

415 H, 1 101

H, 2+ 312

Number of Trips per Day Generated

Trip Generation

Rates Based on Activity (Attraction Rates)

Attractions per

Household

Attractions per

Non-Retail Employee

Attractions per Downtown

Retail Employee

Attractions per Other

Retail Employee

HBW -- 1.7 1.7 1.7

HBO 1.0 2.0 5.0 10.0

NHB 1.0 1.0 3.0 5.0

Trip Attraction Example

Employed at a downtown commercial center are 220 retail

and 650 non-retail workers. Determine the number of trips

per day attracted to this zone.

Process by which trips generated in one

zone are allocated to other zones

Trip Distribution

Basic Methods

Gravity Models

Growth Factor

Trip Distribution

Trip Distribution

A study area consist

of three zones.

Assume Kij is the

same for all zones.

Trip Distribution Example

Trip Productions and Attractions

Zone 1 2 3 Total

Productions 140 330 280 750

Attractions 300 270 180 750

Travel Time Between Zones

Zone 1 2 3

1 5 2 3

2 2 6 6

3 3 6 5


Time (min) F 1 82 2 52 3 50 4 41 5 39 6 26 7 20 8 13

Travel Time Versus Friction Factor


Zone 1 2 3 P

1 47 57 36 140

2 188 85 57 330

3 144 68 68 280

Computed A 379 210 161 750

Given A 300 270 180 750

Zone to Zone Trips: First Iteration


Ajk = Adjusted attraction factor for zone j, iteration k

Cjk = Actual attraction total for zone j, iteration k

Aj = Desired attraction total for attraction zone j


Zone 1 2 3 P

1 34 68 38 140

2 153 112 65 330

3 116 88 76 280

Computed A 303 268 179 750

Given A 300 270 180 750

Zone to Zone Trips: Second Iteration

Trip Distribution Growth Factor Model

Tij = number of trips estimated from zone i to zone j ti = present trip generation in zone i Gx = growth factor of zone x Ti = tiGi = future trip generation in zone i tix = number of trips between zone i and other zones x tij = present trips between zone i and zones j Gj = growth factor of zone j

A study area consists of four zones. The number of trips

between each zone and growth factor for 5 years is shown.

Determine the number of trips between each zone for future

conditions.


Zone Present Trip Generation (trips/day)

Growth Factor

Trip Generation in 5 years

A 600 1.2 720

B 700 1.1 770

C 700 1.4 980

D 400 1.3 520


Zone A B C D

A -- 400 100 100

B 400 -- 300 --

C 100 300 -- 300

D 100 -- 300 --

Total 600 700 700 400

Present Trips Between Zones


Zone A B C D Estimated Total Trip Generation

Actual Trip Generation

A -- 428 141 124 693 720

B 428 -- 372 -- 800 770

C 141 372 -- 430 943 980

D 124 -- 430 -- 554 520

Totals 693 800 943 554

First Estimate of Trips Between Zones

Process to determine the number (or percentage) of trips

between zones that are made by various modes (auto,

carpool, transit, bike/walk)

Mode Choice

Mode Choice

Determine the number of transit trips per day in a zone

which has 5000 people living on 50 acres. The auto

ownership is 40% with zero autos per household and 60%

with one auto per household.

Mode Choice Example

Process to determine the actual routes that travelers will use

Traffic Assignment

Basic Methods

Diversion Curves

Minimum Time Path

Minimum Time Path with Capacity Restraint

Traffic Assignment

Traffic Assignment

Dr. Lina Shbeeb 53

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