6 alternative demand models

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Alternative demandmodels

CIVL1011/CIVL2111Transportation Engineering


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Trip interchangeusage model

Trip end model

Trip distribution

Trip generation

Modal choice

Trip assignment

Modal choice

Trip generation

Trip distribution

Trip assignment

Alternative demandforecasting model structure 1


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4.11d

(mode)


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Trip distribution

Trip generation

Modal choice

Trip assignment

Trip generationand

mode choice

Trip distribution

Trip assignment


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Trip interchange usage model

Trip distribution

Trip generation

Modal choice

Trip assignment

This approachfacilitates theinclusion of the

characteristics ofthe journey andthose of thealternatives modes

Trip ends

Trips-by-destination

Trips-by-mode-by-destination

Trip interchangeusage model


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Trip generationand

mode choice

Trip distribution

Trip assignment

Direct generation usage model

This approach is appropriate to

smaller urban areas withoutmajor transit service.

trips-by-mode

Trips-by-mode-by-destination

Direct generation

usage model

No indicationto where thosetrips might go.


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Combined trip generation andmode choice models

a. Cross-classification model


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Combined trip generation andmode choice models

b. Regression models Connecting trips-by-modeto population (POP), income

(INC), and automobiles (AUTO):

Mainly consider characteristics of trip makers. Can the model

capture trip length? capture fare of bus? Use to study fare reduction policy?

AUTOCPOPBAautoT

INCCPOPBAtransitT


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Mode anddestination

choices

Trip generation

Trip assignment

Trip distribution

Trip generation

Modal choice

Trip assignment



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Combined mode anddestination choice model

Multinomial Logit model

Example: utility function in Logit model

Vmd = Bo BTT + BAAwhere

Vmd = utility of an individual for selecting for the

combination of mode m and destination dT = travel time in minutes

A = commercial floor area in thousand ft2

BA, BT = positive parameters

,

md

ns

V

md V

n s

eP

e


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Example

Ajoint shopping-trip mode-destination choice logit model is estimated,giving the following coefficient:

a. determine the distribution of trips by destination and mode.

variable Auto coefficient Bus coefficient

Auto constant 0.6 0Travel time in minutes -0.3 -0.3

Commercial floor space (in

thousand of m2)

0.12 0.12

R

2

1Residential,1000 trips

Shopping area=25000 m2

8 min

10 min

14 min

20 min

Shopping area

=40000 m2

bus

car


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Example solution

a. Let Vmdbe the utility of going to shopping center d via mode m

1

1

2

2

0.6 0.3 8 0.12 25 1.2

0.3 14 0.12 25 1.2

0.6 0.3 10 0.12 40 2.4

0.3 20 0.12 40 1.2

A

B

A

B

V

V

V

V

m d Vmd Pmd Trips by m to shopping center d

Car 1 1.20 3.32 0.222 222bus 1 -1.20 0.30 0.020 20

Car 2 2.40 11.02 0.738 738

bus 2 -1.20 0.30 0.020 20

sum 14.95 1.000 1000

mdVe

-md o T AV B B T B A


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Example

To attract as many total trips as it did before the congestion,

how much commercial floor space must be added toshopping center 2?

R

2

1Residential,1000 trips

Shopping area= 25000 m2

8 min

10 + 4 min

14 min

20 + 4 min Shopping area= 40000 + ? m2

bus

Car


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Example

Solution

Let x be the increase in floor space.

To attract as many total trips as it did before the congestion, theproportions and hence the utilities of all modes to center 2 must be thesame as those before the congestion. Hence

x=10

Therefore, a commercial floor space of 10000 m2 must be added.

2

2

0.6 0.3 10 4 0.12 40 2.4,and

0.3 20 4 0.12 40 1.2

A

B

V x

V x


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Trip distribution

Trip generation

Modal choice

Trip assignment


Direct demand

Trip assignment


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Direct demand model example 1

4 6 8

2 3 5 7 91

0

between zonestravel volum and via mode

of zone ( )

between zon

landuse v

least c

pop

ost

ariaulation b

e

e

e

l

a a a

a a a a aa ijk ijk ijk

ijk i j ij ij ij ijij ij ij

ijk

i

ij

C H D

T a P P C H D Y C H D

T i j k

P i

C

s andbetween zones and via mode

between zone

travel time

s and

between zones and via mode

be

shortest travel tim

departure frequency of most frequency t

co

mod

s

e

e

e w

tijk

ij

ijk

ij

i jC i j k

H i j

H i j k

D

en zones and

between zones and via m

weighted average inc

d

o

ode

of and ( )

param

socioeconomic variablm

eparture fr

e

equency

s

t

e

er

e

ijk

ij

l

i j

D i j k

Y i j

a l

interzonal

impedence

variables


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4 6 8

2 3 5 7 9

4 6 8

2 3 5 71 9

1

0

0

1

1

a a aa a a a aijk ijk ijk

j ij ij ij ij

ij ij ij

a a a

a a a a aijk ijk ijk

j ij ij ij ijij ij ij

ijk i

i ijk

ii

i

a

a

T Pe

P T

P

P

C H DP C H D Y

C H D

C H DP C H D Y

aa

aH

P

C D

Example

Determine the elasticity of demand with respect to population i,

of the direct demand model

Solution

4 6 8

2 3 5 7 91

0

a a a

a a a a aa ijk ijk ijk

ijk i j ij ij ij ij

ij ij ij

C H DT a P P C H D Y

C H D

The exponent!

ijk i

i ijk

T Pe

P T

1a


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Example Using the direct demand model shown before to determine the

percentage change in the patronage of mode k serving between zone iand j if the travel time between zone i and j by mode k is reduced by20%. Assume a6=-2

Solution Let beforeand afterbe the subscripts before and after reduction

respectively.

Let also

4 6 8

2 3 5 7 91

0

1a a a

a a a a aa ijk ijk

i j ij ij ij ij

ij ij ij

C Da P P C H D Y

C H D

, , ,(1 0.2) 0.8ijk after ijk before ijk beforeH H H

, , ,

, ,

100% 1 100%ijk after ijk before ijk after

ijk before ijk before

T T T

T T

= 56.25% increase

2

,,

2

, ,

after ijk after ijk after

ijk before before ijk before

HTT H

20.8 1.56251


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Direct demand model example 2

peak

Destination 1

Off-peak

Choice

No tripTrip

Mode 1

Destination N

Mode KMode 1 Mode K

Destination 1

Mode 1

Destination N

Mode KMode 1 Mode K

How many levels?How many nests?

How many choices?

A combined trip-generation, time-of-day, destinationand mode choicenested logit model


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Direct demand model -example 3

Elastic demand model

TAC: travel time

VAC: travel demand

248 4AC AC

T v


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Demand supply equilibrium

At demand-supply equilibrium, the travel time spent byeach traveler is equal to the travel time provided by thenetwork.

Travel timebetween originand destination

Traveldemand

Supply

functionDemandfunction

Equilibriumtravel time

Equilibrium demand

Direct demand

Trip assignment


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Example

Given the network and performance functions below, find the

equilibrium travel demand and travel times if the demand function is

.

Solution

8 6 248 4AC ACv v

8 6 24 152ACT

A B C

Link 1:T1= 4 + 2v1

Link2:T2 = 4 +4 v2

(Demand = supply)

8

TAC

vAC

152

24

6

248 4AC ACT v

8 6AC ACT v

248 4AC ACT v

1 2 1 24 2 4 4

8 6

AC

AC

T T T v v

v

1 2ACv v v

1 1

2 2

4 2 4 2(24) 52

4 4 4 4(24) 100

T v

T v

1 210 240 24AC ACv v v v


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Trip distribution

Trip generation

Modal choice

Trip assignment


Trip distribution

Trip generation

Modal choice

Trip assignment

6 alternative demand models

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