Trip generation
Trip generation modeling is to develop an expression that predicts exactly when a trip is
to be made.
Trip generation is a first stage of classical first generation aggregate demand model
• Aim of trip generation is to predict a number generated or attracted to each zone of the
study area
• There is two main modeling of trip generation
• Growth Factor Modeling
• Regression Modeling
Types Of Trips
• Trips are Classified Into Home-Based Trips And Non-home based Trips
Factors Affecting Trip Generation
• The Main Factors affecting trip generation Include
• Income
• Vehicle Ownership
• House Hold Structure
• Family Size
Trip distribution
Trip distribution is a process by which the trips generated in one zone are allocated to other zones in
the study area.
These trips may be within the study area (internal-internal) or between the study area and areas
outside the study area (internalexternal).
For example, if the trip generation analysis results in an estimate of 200 HBW trips in zone 10, Then
the trip distribution analysis would determine how many of these trips would be made between
zone 10 and all the other internal zones.In addition, the trip distribution process considers internal-
external trips (or vice versa) where one end of the trip is within the study area and the other end is
outside the area.
Several basic methods are used for trip distribution. Among these are:
- Gravity model
- Growth factor models
- Intervening opportunities model.
Mode choice
Mode Choice is aspect of demand analysis process that determines the number (or %) of trips
between zones made by modes (auto, bus..)
✔ Selection of a mode is a complex process that depends on factors such as the income,
availability of transit/auto ownership, and the relative advantages of modes (tt, cost, safety,..)
Types of mode choice model.
✓ Auto
✓ Transit
Depending on the level of detail required, three types of transit estimating procedures are
used:
(1) direct generation of transit trips,
(2) use of trip end models, and
(3) trip interchange modal split models.
Factors influencing the choice of modeThe factors may be listed under three groups:
1. Characteristics of the trip maker
The following features are found to be important:
(a) car availability and/or ownership;
(b) possession of a driving license;
(c) household structure (young couple, couple with children, retired people etc.);
(d) income .
e) decisions made elsewhere, for example the need to use a car at work, take children to school, etc;
(f) residential density.
2. Characteristics of the journey:
Mode choice is strongly influenced by:
(a) The trip purpose; for example, the journey to work is normally easier to undertake by public
transport than other journeys because of its regularity and the adjustment possible in the long run;
(b) Time of the day when the journey is undertaken.
(c) Late trips are more difficult to accommodate by public transport.
3. Characteristics of the transport facility
There are two types of factors.One is quantitative and theother is qualitative.
Quantitative factors are:
(a) relative travel time: in-vehicle, waiting and walking times by each mode;
(b) relative monetary costs (fares, fuel and direct costs);
(c) availability and cost of parking
Qualitative factors which are less easy to measure are:
(a) comfort and convenience
(b) reliability and regularity
(c) protection, security.
Trip End Models
The procedure is as follows:
1. Generate total person trip productions and
attractions by trip purpose.
2. Compute the urban travel factor.
3. Determine the percentage of these trips by
transit using a mode choice curve.
4. Apply auto occupancy factors.
5. Distribute transit and auto trips separately.
Trip Interchange Models
(1) distance between zones by auto and transit,
(2) transit fare,
(3) out-of-pocket auto cost,
(4) parking cost,
(5) highway and transit speed,
(6) exponent values, b,
(7) median income, and
(8) excess time (inc. time to walk to a transit vehicle and time waiting or transferring).
Compare trip end models and direct generation models
Direct Generation Models
This method assumes that the attributes of the system are not relevant.
✓ Factors such as travel time, cost, and convenience are not considered.
✓ These so-called “pre-trip distribution” models apply when transit service is poor and riders
are “captive,” or when transit service is excellent and “choice” clearly favors transit.
✓ When highway and transit modes “compete” for
auto riders, then system factors are considered.
Trip End models
✓ To determine the no. or % of persons trips that will use transit, estimates are made
prior to the trip distribution phase based on land-use or socioeconomic
characteristics of the zone.
✓ This method does not include quality of service.
✓ The model of Figure 12.9, is based on factors: households/auto and persons/mile 2
✓ The product of these factors is the urban travel
factor (UTF).
✓ %of transit trips increase as UTF increases
Binary logit model is the simplest form of mode choice, where the travel choice between two modes
is made.
Traffic assignment
✓ The basic approaches that can be used for
traffic assignment purposes are:
(1) diversion curves,
(2) minimum time path (all-or-nothing)
assignment, and
(3) minimum time path with capacity restraint,
and
(4) equilibrium approach, which is divided into
System Optimal, or User Equilibrium.
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