Module 3.1: Transport Demand Flashcards by Amy Magnani

What is transport supply?

Transport supply:

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

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What is transport demand?

Transport demand:

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

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What is transport planning?

Transport planning aims to achieve equilibrium between demand and supply

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What is a transport model?

Simplified representation of the real world transport network

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What are zones?

Aggregations of individual land parcels into manageable divisions

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What is a network?

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

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What are the 3 main areas of land use data?

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

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What areas does travel data involve?

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

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What are the types of travel surveys?

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

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What info does a household travel survey involve?

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

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What is the 4-step transport model?

Trip generation
Trip distribution
Modal Split
Assignment

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What percentage of trips at home-based?

85%

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What is a trip production?

home end of a HB trip

- origin of a NHB trip

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What is a trip attraction?

non-home end of a HB trip

- destination of a NHB trip

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What factors affect trip productions & attractions?

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

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What are the 3 model forms?

Growth factor modelling
Category analysis
Regression analysis

What is growth factor modelling?

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

What is category analysis?

Popular in US and UK

Estimates average trip rates as function of household attributes

What is regression analysis?

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

What is a dummy variable regression?

Variables take on a value of 0 or 1

e.g. male: 0, female: 1

Describe how Productions & Attractions are equated?

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

What do Trip generation models ignore?

impact of transport supply
congestion
accessibility on trip making

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

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

What is a gravity model?

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

What are the 3 forms of deterrence functions?

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

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

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,

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

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

What are the 3 types of trip assignment?

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

What is the All-or-Nothing assignment?

``` 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 ```

What is Stochastic assignment?

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

What is Wardrop's Equilibrium?

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

What is Capacity Restraint method?

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