Module 3.1: Transport Demand

Question 1

What is transport supply?

Answer 1

Transport supply:

• is a service
• requires number of fixed assets
• requires set rules for operation

Question 2

What is transport demand?

Answer 2

Transport demand:

• is a derived demand
• takes place over space
• is highly differentiated
• has strong dynamic elements

Question 3

What is transport planning?

Answer 3

Transport planning aims to achieve equilibrium between demand and supply

Question 4

What is a transport model?

Answer 4

Simplified representation of the real world transport network

Question 5

What are zones?

Answer 5

Aggregations of individual land parcels into manageable divisions

Question 6

What is a network?

Answer 6

Made up of nodes & links that represent roads & routes, lower order roads/routes may be ignored/aggregated

Question 7

What are the 3 main areas of land use data?

Answer 7

• Population (age, income, car ownership, activity status)
• Employment (occupation, industry)
• Education (enrolments by type or level)

Question 8

What areas does travel data involve?

Answer 8

• number of trips per day
• average trip length
• trip purpose
• mode
• time of day
• socio-demographic

Question 9

What are the types of travel surveys?

Answer 9

Observation: traffic count, boardings/alightings, number plate, bluetooth
Interview: roadside, on-board, household

Question 10

What info does a household travel survey involve?

Answer 10

• household: number of persons, vehicles
• vehicles: type, ownership, age
• persons: age, gender, disabilities
• trips: in a nominated travel day

Question 11

What is the 4-step transport model?

Answer 11

1. Trip generation
2. Trip distribution
3. Modal Split
4. Assignment

Question 12

What percentage of trips at home-based?

Answer 12

85%

Question 13

What is a trip production?

Answer 13

• home end of a HB trip

- origin of a NHB trip

Question 14

What is a trip attraction?

Answer 14

• non-home end of a HB trip

- destination of a NHB trip

Question 15

What factors affect trip productions & attractions?

Answer 15

Productions: household size, income & car ownership
Attractions: population, employment, enrolments

Question 16

What are the 3 model forms?

Answer 16

1. Growth factor modelling
2. Category analysis
3. Regression analysis

Question 17

What is growth factor modelling?

Answer 17

Crude but simple
Relies on pre-existing estimates & a measure of growth
Suitable for developed areas, short term (≤3 years), external trips
Ti = Fi.ti
Ti: future trips, ti: existing trips, Fi: growth factor

Question 18

What is category analysis?

Answer 18

Popular in US and UK

Estimates average trip rates as function of household attributes

Question 19

What is regression analysis?

Answer 19

Dependent variable (e.g. attractions) is estimated from independent variables (e.g. population, employment)
Yi = ∑bX + c + ei
b: coefficient
X: independent variable
c: constant, ei: error

Question 20

What is a dummy variable regression?

Answer 20

Variables take on a value of 0 or 1

e.g. male: 0, female: 1

Question 21

Describe how Productions & Attractions are equated?

Answer 21

No guarantee that ∑P = ∑A
Factor A’s by a factor: ƒ = ∑P / ∑A
This assumes that the production models are ‘better’

Question 22

What do Trip generation models ignore?

Answer 22

• impact of transport supply
• congestion
• accessibility on trip making

Question 23

What is doubly constrained growth factoring? What are the limitation?

Answer 23

Different growth rates for origin & destination, requires iterative solutions
Tij = tij x ai x bj
Limitations:
- needs a starting matrix & expected trip growth
- suitable only for short term 1-2years
- zero cells remain zero cells

Question 24

What is a gravity model?

Answer 24

• used when there are changes in a network
• doesn’t rely on existing trip matrix (synthetic)
  Tij = ai x bj x ƒ(cij)
  cij: generalised cost, ƒ(cij): deterrence function

Question 25

What are the 3 forms of deterrence functions?

Answer 25

Power: ƒ(c) = c^a
Exponential: ƒ(c) = e^(ßc)
Gamma: ƒ(c) = c^a x e^(ßc)

Question 26

What is matrix estimation? What are the pro’s & con’s?

Answer 26

Use traffic counts as ‘targets’ that are reproduced by changing the values in matrix cells
Pro’s: simple, good reproduction of traffic flows, minimal data required
Con’s: errors from inconsistency, over-estimates, single trip purpose only,

Question 27

Describe a model split curve (a.k.a. diversion curve).

Answer 27

Probability of using Mode 1 vs. Cost difference (C2-C1)
‘S’-shaped
Modal penalty: ∂ - some modes are preferred over others, even when the cost is equal

Question 28

What are the 3 types of trip assignment?

Answer 28

1. All or nothing (AON)
2. Stochastic
3. Capacity restraint

Question 29

What is the All-or-Nothing assignment?

Answer 29

Assumptions:
- route chosen that minimises cost of travel
Useful for:
- un-congested networks
Con's:
- ignores link capacity & congestion
- sensitive to small changes in cost

Question 30

What is Stochastic assignment?

Answer 30

- considers 2nd, 3rd, 4th best routes
Pro's:
- reasonable spread
- relatively simple
Con's:
- ignores congestion effects

Question 31

What is Wardrop’s Equilibrium?

Answer 31

Under equilibrium conditions, traffic arranges itself in congested networks such that all routes have equal and minimum costs
i.e. traffic arranges itself such that no individual can reduce their costs by switching route

Question 32

What is Capacity Restraint method?

Answer 32

• incremental assignment
• typical values: 40%, 30%, 20%, 10%
  Pro’s:
• good convergence
  Con’s
• cannot remove loading of flow