Lec 11 TDPart 4: 5.4.3

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Lec 11 TD-Part 4 5.4.3 5.5.1, H/O pp.491 Mode
Usage (modal split) and Intro to trip assignment
Lecture Objectives

• Understand why modal split needs to be done
  (5.4.3)
• Understand the difference between
  Direct-generation usage models (Trip-end models)
  and Trip-interchange mode usage models (H/O, pp.
  491 -)
• Understand the meaning of the logit formulation
  (5.5.1)
• Learn how to use these models (H/O, pp. 491 -)

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What is modal split?

• Split trips to different available
  transportation modes, by analyzing peoples
  decisions regarding mode of travel they use.

Can be done here
Trip-end models vs. Trip-interchange models
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What affects peoples mode choice?
Characteristics of the trip trip distance, time
of day, trip purpose
Characteristics of the trip maker Income, of
autos available, family size, residential
density, gender
Characteristics of the transportation system
riding time, waiting time, transfers,
out-of-pocket cost
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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
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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
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Trip-interchange models
Influencing all three phases.
Trip-interchange models are used AFTER the trip
distribution phase.
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Trip-interchange models (cont)
Competing modes
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.
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Trip-interchange models (cont)
Lets see how service and trip makers
characteristics can affect the trip makers
decision using Fig. 11-11.

• In-vehicle time (Auto Transit) -15 min
• Out of pocket cost (Auto Transit) 25 cents
• Excess time (Auto Transit) 3 min
• If so, 37 of trips will be made by transit.

Looks like a logit curve
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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)