Transport Demand - Trip Generation

Question 1

What is the 4 - Step Transport Model?

Answer 1

Inputs:
Land Use Data
Travel Data
Zones and Networks

---------
Process:
--->Trip Generation 
    --> Trip Distribution 
      --> Modal Splits 
         --> Assignment
          ---->Evaluation

Question 2

What is a trip?

Answer 2

One way movement from A to B

Question 3

What is a Home based trip?

Answer 3

A trip with one end at home

Question 4

What is a non-home based trip?

Answer 4

A trip with neither end at home

Question 5

What is trip purpose?

Answer 5

Determined by activity at the non-home end of a home based trip

Question 6

What percentage of trips start or end at home?

Answer 6

85%

Question 7

What is trip production?

Answer 7

The home end of the HB trip or the origin of a NHB trip

Question 8

What is trip attraction?

Answer 8

Non home end of a HB trip or the destination of a NHB trip

Question 9

What is trip generation?

Answer 9

The process of estimating productions and attractions for each zone in the model

Question 10

What factors affect trip generation?

Answer 10

Trip production:

• household size
• income and car ownership

Trip attractions:

• population
• employment
• enrolements

Question 11

What are the three types of model forms?

Answer 11

• Growth Factor Modelling
• Category Analysis
• Regression Analysis

Question 12

What is growth factor modelling?

Answer 12

Ti = Fi ti
Ti= future trips to/from zone i
ti = existing trips to/from zone i
Fi = growth factor (depends on population, income, car ownership)

Relies on a pre-existing estimate of productions and some measure of growth

Question 13

What is category analysis?

Answer 13

Estimates average trip rates as a function of household attributes (common on UK and US)

Categories should:

• be large enough for sufficient data
• minimise intra category variation in trip rates

Issues:

• no statistical goodness of fit
• cannot extrapolate
• no effective way of choosing variables

Question 14

What is regression analysis?

Answer 14

A dependent variable is estimated from a set of independent variables
Yi = ∑ bk Xki + c + ei

Where bk = the coefficient for the kth parameter
Xki = the kth independent variable for zone i
c= constant or intercept
ei = the error or disturbance term

Question 15

What are the three stats test that are important?

Answer 15

• t-test = significance of independent variables
• F -test - significance of the whole equation
• R^2 = proportion of variation explained

Question 16

What is zone based regression?

Answer 16

An equation that deals with zonal total trip ends - based on zonal attributes
- have a large constant term
- coefficients depend upon the zone system used
- often used for trip attraction modelling
e.g.
Trips = 1.23 X populationi + 1.10xEmploymenti + 750

Question 17

What is household based regression?

Answer 17

Deal with household trips ends
Trips = NumHHi ( … x Persons/HH + .. Workers /HH+ … Cars/HH + …)

Fewer independent variables gives better relationship forms
Relationships tend to be geographically and temporally stable
Greater variation between households

Question 18

What is dummy variable regression?

Answer 18

Dummy variables - take on a value of 0 or 1, depending on the absence or presences of pre-defined effect

• Capture non-linearity between trip rates and independent variables
• Developed at the household level but applied at the zonal level

Question 19

Must Productions and attractions equal? and if so why is this required?

If attractions dont equal productions what is the pragmatic solution?

Answer 19

Yes, there is no guarantee that they will but the ∑Ai = ∑Pi

Required because conservation of matter and for trip distribution

Pragmatic solution is to factor Attractions (Ai) by a factor f to equal productions

Question 20

What are the implementation issues for models?

Answer 20

• Assume that model parameters do not change with time ( once calibrated model coefficients remain constant)
• Assume geographically stable
• Challenges remains to forecast the various input variables
• Trip generation modes ignore the impact of transport supply, congestion and accessibility on trip making

Question 21

What are the stability parameters?

Answer 21

• Temporal Stability

- Geographic stability

Question 22

How are input variables forecasted?

Answer 22

• Production variables (number of households, average people, workers, dependents and cars per household)
• Attraction variables (employment, enrolments)

Question 23

True or False

Any errors in forecasting input variables will flow through the rest of the 4-step process

Answer 23

True

Question 24

Why is trip generation considered inelastic?

Answer 24

• the network has no effect on trip generation
• unlikely to be true for discretionary trips
• one possible solution
  
  • incorporate accessibility in trip generation model - but research has found that accessibility is not significant in models

Question 25

What is trip chaining?

Answer 25

Linking trips together

Challenge is to model the number and location of intermediate stops along the tour - traditional methods focus more on origin/destination (HB)

Question 26

What is activity modelling?

Answer 26

• Treat travel as part of set of wider household activities which are categorised by “need” or “function”

Question 27

What is trip generation?

Answer 27

How many trips start and end in a zone?