Transport Modelling– An
overview of the
four modeling stages
Prof. Dr. Mir Shabbar Ali
Lecture covers
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•
•
•
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Travel demand modeling concepts
Four stage TDM
Explanation
Data requirements
Forecasting
TRAVEL DEMAND ANALYSIS; MODELLING AND FORECASTING
The Four Stage TDM
The fours
step
process
Key Concepts in transportation
planning Model
Interaction
• Long-run decrease in friction of distance
t1
t2
t3
Distance
Due to innovations in transportation methods
and improvements in media themselves
Result: Lowered average ton-mile costs of transportation
and decreased importance of transport costs as a
factor cost  AND other costs rise in importance
Four basic elements of the urban
transportation forecasting process
Data collection
(population, land
use, etc.)
Economic activity (employment, sales volume, income,
etc.), land use (type, intensity), travel characteristics (trip
and traveler profile), and transportation facilities (capacity,
travel speed, etc.), population and demography, Origindestination trip data.
Analysis of existing
conditions and
calibration
Analyze the data collected in the data collection stage. You
may build mathematical models describe the existing
conditions and then use the relationships you have found
in the existing parameters to forecast future values.
Forecast of future
travel demand
4-step transportation demand forecasting process
Analysis of the
results
Analyze what you get from the 4-stop demand forecasting
process
Comprehensive Transportation
Planning Dimensions
• Economic
• Social
• Environmental
Why Use Travel Demand Models
• A relationship between transport system and
indicators
– Access
– Purpose
– Frequency
– Use
Land use
Travel behavior
T
TRAVEL
DEMAND
MODEL
System performance
Economic, Social, and Environmental
Dimensions
• Where do they come in to this process?
TRAVEL
DEMAND
MODEL
System performance
Other data
Indicators
Evaluate
progress to
goal
…through performance indicators
• For example:
– Commute speed
– Land use mix
– Transport diversity
– Transport equity
Residential
Employmen
t
Residential Employmen
t
Service
Service
Example
• Model output = travel times between all
points
• Indicator: Commute speed
• Indicator: Land use mix
• Indicator: Transport diversity
• Indicator: Equity
Introduction to Travel Demand
Modeling
• What is a travel demand model
• Assignment: Discuss your knowledge
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–
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Input data
Trip generation
Trip distribution
Mode choice
Traffic/trip assignment
Land use
Travel behavior
T
TRAVEL
DEMAND
MODEL
System performance
Four Step Travel Demand Model
(FSTDM)
Demographic
Data
Step 1: Trip
Generation
Transportation
Network
Step 2: Trip
Distribution
Step 3: Mode
Choice
Step 4: Trip/ Traffic
Assignment
Trip Generation Questions
• How much do people use the transport
system?
• Why do people use the transport system?
• Where can different types of activities be
satisfied?
Productions and Attractions
Types of Urban Movements
Movement
Type
Pendular
Pattern
Dominant Time Destination
Structured
Professional
Varied
Morning and
afternoon
Workdays
Localized
(employment)
Localized
Personal
Structured
Evening
Touristic
Seasonal
Day
Varied with
some foci
Highly localized
Distribution
Structured
Nighttime
Localized
Cross Classification Model
Number of trips by household classifications or
grouping
Trip Distribution Questions
• Given a location, where do people go to
satisfy demand for an activity type?
Trip Distribution Models
• Gravity Model
– Tij = Ti
•
•
•
•
•
a
Aj / Cij
a
Sum (Ax / Cix)
You can consider this as the
probability spatial distribution
P(Tj)
Tij = trips from zone i to zone j
Ti = total trips originating at zone i
Aj = attraction factor at j
Ax = attraction factor at any zone x
Cij = travel friction from i to j expressed as a generalized cost
function
• Cix = travel friction from i to any zone x expressed as a
generalized cost function
• a = friction exponent or restraining influence
O - D Matrix Example:
Origins
1
2
3
4
5
6
Sum
1
T11
T21
T31
T41
T51
T61
D1
2
T12
T22
T32
T42
T52
T62
D2
Destinations
3 4 5
6
T13 T14 T15 T16
T23 T24 T25 T26
T33 T34 T35 T36
T43 T44 T45 T46
T53 T54 T55 T56
T63 T64 T65 T66
D3 D4 D5 D6
Sum
O1
O2
O3
O4
O5
O6
What is modal split?
Split trips to different available
transportation modes, by
analyzing people’s decisions
regarding mode of travel they
use.
Trip-end models
vs.
Trip-interchange models
Can be
done
here
Mode choice Questions
• How do people use the transport system?
– What modes do they choose?
– How do they react to varying transport service
quality?
What affects people’s mode choice?
Characteristics of the trip: trip
distance, time of day, trip purpose
Characteristics of the trip
maker: Income, # of autos
Characteristics of the
transportation system:
riding time, waiting
time, transfers, out-ofpocket cost
available, family size,
residential density, gender
Direct-generation usage models
(Trip-end models)
Generate trips for transit and
highway users separately 
meaning transit users use
only transit (“captive” users).
Used for small
communities or in
developing countries
where ridership is primarily
a function of
socioeconomic variables
Direct-generation usage models
(Trip-end models) (cont)
Same categories but different
trip rates
Or, use separate models, like:
P(T) = A + B(POP) – C(INC)
P(A) = A + B (POP) – C(AUTO)
Advantage: Simplicity
Disadvantage: Cannot reflect
“change of mind” of trip
makers responding to policy
and service changes
Trip-interchange models
Influencing all
three phases.
Trip-interchange models are used AFTER the trip distribution phase.
Trip-interchange models (cont)
Because trip-interchange models are used after trip
distribution, they can utilize the service characteristics
of the modes available for the given trip, along with
any relevant socioeconomic characteristics to
determine the modal splits. This is the preferred and
overwhelmingly typical approach for urban areas in
which significant transit service exists and in which
the “competition” between auto, transit, and other
modes of travel must be explicitly considered.
Trip-interchange models (cont)
Let’s see how service and trip makers characteristics can
affect the trip maker’s decision using Fig. 11-11.
1. In-vehicle time (Auto
– Transit) = -15 min
2. Out of pocket cost
(Auto – Transit) = 25
cents
3. Excess time (Auto –
Transit) = 3 min
4. If so, 37% of trips will
be made by transit.
Looks like a logit
curve…
Use of logit
models for
modal choice
(“Disaggregate, random utility
modal choice model”)
The logit model trades off the
relative utilities of various
modes.
“The better a mode is,
the more utility it has
for the potential user”
(See Examples
11& 12)
Trip / Traffic Assignment Questions
• How do people use the transport system?
– Given a mode, which route do they choose?
– Do they satisfy multiple activities in one tour?
– Which parts of the transport system do they use?
– How do they react to varying transport service
quality?
Network Level of Service
 Highway
 Travel distance ij
 Travel time ij
 Travel Cost
 Transit
 Walk time ij
 First wait ij
 In-vehicle time ij
 Transfer time ij
 Fare ij
 Number of transfers
 Drive access areas
 Walk access areas
Road Sections with more than
100,000 Vehicles/Day
Top 20 Road Sections in terms of
Traffic Volume
Demographic Data
• Autos per household
• Income level
• Household size
Network Data
• Highway network
• Transit network
• Graph
Representing a Network
Explanations and working
Transit Access Coding
AM Peak Period Bus Travel Time
Factor
SERVICE
AREA TYPE
FACILITY TYPE
TRAVEL TIME
FACTOR
EXPRESS
1-5
FREEWAYS
1.44
EXPRESS
1-3
SURFACE ROADS
1.53
EXPRESS
4-5
SURFACE ROADS
1.83
LOCAL
1-3
ALL
1.66
LOCAL
4-5
ALL
1.90
SHUTTLE
1-5
ALL
3.00
Carbon Monoxide Concentrations
Projected for December 1995
Thanks