Pekol (Transport Demand Modelling - Trip Generation) Flashcards
What is the 4-Step transport model?
Land Use Data + Travel Data + Zones & Network >Trip generation >Trip distribution >Modal split >Assignment
What question does trip generation attempt to answer?
How many trips start and end in a zone
What is a Home Based (HB) trip?
A trip with one end at home
What is a Non Home-Based (NHB) trip?
A trip with neither end at home
How is the trip purpose found?
Determined by the activity at the non-home end of a home based trip
What percentage of trips start or end at home?
85%
What is trip generation?
The process of estimating productions and attractions for each zone in the model
What are some trip productions?
- Household size
- Income and car ownership
What are some trip attractions?
- Population
- Employment
- Enrolments
What are some forms of models?
- Growth factor modelling
- Category analysis
- Regression analysis
What is Category analysis?
- Not very popular in Aus.
- Estimates average trip rates as a function of household attributes (uses 3*3 matrix)
What does growth factor modelling rely on?
Pre-existing estimate of productions and some measures of growth
When is growth factor modelling appropriate?
- developed areas
- short term forecasts (<3years)
- external trips
What is the formula for Growth factor modelling?
Ti=Fi*ti Where: Ti=future trips to/from zone ti=existing trips to/from zone Fi=growth factor
What is Regression analysis?
A dependant variable (e.g attractions) is estimated from a set of independent variables (e.g population,employment)
What does a zonal based regression deal with?
Zonal total trip ends
>there is one regression equation per trip purpose
What does a Household based regression deal with?
Household trip ends
Attempts to find trips per individual household
Wht are the benefits of Household Based Regression?
- Fewer independent variables give better relationship forms
- Relationships tend to be geographically and temporally stable
What is a disadvantage of Household based regression?
Greater variation between households.
Due to huge variation in input data, lower R^2 values
What are the key components of Dummy Variable regression?
- Dummy variables take on value 0 or 1 (e.g smoker=1, non-smoker=0)
- Captures non-linearity between trip rates and independent variables
- Developed at the household level, but applied at the zonal level
Why do we need the attractions to equal productions?
- Conservation of matter (trips)
- Trip distribution (the next step)
How do we account for the fact that attractions do not always equal productions?
Pragmatic solution is to factor attractions by f.
What are some implementation issues?
- we assume that model parameters do not change with time (once calibrated, model coefficients remain constant)
- Often assumed to be geographically stable
- Challenge remains to forecast the various input variables
- Trip generation models ignore the impacts of transport supply, congestion and accessibility on tip makings (i.e. nothing relates to transport network itself)
What is a major disadvantage of the four-step process?
- the network has no effect on trip generation
- Unlikely to be true for discretionary trips
What is a possible solutions to change the four-step method from not having the network affect trip generation?
Incorporate accessibility into trip generation model.
research has found that accessibility is not significant in aggregate models
What is activity modelling?
- Treat travel as part of set of wider household activities
- Activities are categorised by “need” or “function”
Are production and attraction the same as origin and destination?
NO. No. No NO NO NO.
