Lec 26: Ch3.(T

1
Lec 26 Ch3.(TLD) Traffic Analysis Trip
generation

• Know the definition of site-oriented and non-site
  traffic
• Understand the phases of site impact traffic
  evaluation (S.I.T.E.)
• Learn how to estimate trips generated by a
  development
• Know how to use ITE Trip Generation Handbook

2
Site-oriented traffic vs. Non-site traffic
With the development (new or existing)
Site-oriented traffic (trips having an OD on the
site
Non-site traffic (no OD on the site)
Without the development
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SITE Methodology

• Phase I Establish existing traffic conditions
  without the site (proposed)
• Phase II Forecast future traffic conditions
  without the site
• Phase III Forecast future site-only traffic
  conditions
• Phase IV Determine total future traffic
  conditions (II III)
• Phase V Evaluate alternative improvements
• Phase VI Negotiations
• Phase VII Implementation

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Flow chart of SITE process
Phase I
Existing Background Traffic
Calculate LOS
Phase II
Traffic growth factors
Input from MPO and local/state agencies
Forecast traffic for other new adjacent sites
Future background traffic w/o site
Combine
Calculate LOS
Compare
5
Flow chart of SITE process (cont)
Phase III
Forecast traffic for site development
Phase IV
Combine
Total traffic
Calculate LOS
Compare
6
Flow chart of SITE process (cont)
Phase V
Document findings
Evaluate solutions
Develop alternative solutions
Feedback
Phase VI
Begin negotiations between local officials and
developers
Perform supplemental technical analyses
Feedback
Phase VII
Assist in preparing construction plans
Implementation
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Site-oriented traffic (site-generated trips)
much easier to estimate because

• The land use activities are known
• The number of trips expected to be generated by
  the proposed development can be determined using
  the ITE Trip Generation Handbook
• The present and future directional distribution
  can be estimated

• The total number of trips generated
• The number of trips to and from the site during
  the peak hours of the adjacent street
• The number of trips to and from the site during
  the peak(s) of the generator
• Daily variation
• Monthly variation

5 Primary characteristics
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Unit used as the base variable for
trip-generation rates

• Be functionally related to the volume of traffic
  generated (e.g. 48 trip ends per 1000 sq.ft floor
  area, 5.7 trip ends per occupied dwelling unit)
• Be relatively easy to establish/measure (meaning
  easy to measure the size, like size of an
  household, size of a store)
• Provide consistent and transferable rates
  (Although variations exist, establishments of
  similar characteristics have similar trip
  generation rates.

ITE Trip Generation Handbook
(See the handout)
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Issues (pp. 29, 39, 40)

• Age of data base Not much difference between
  old and new data
• Daily variations Peaking of traffic varies
  depending on the type of development
• Location variation ITE trip generation data
  came from suburban areas (for vehicular trips)
• Pass-by traffic Some generators attract
  traffic from the passing traffic stream
• Mixed-use development Mixed-use land may
  produce less trips than the sum total of
  individual land uses (many rates are derived from
  stand-alone developments)
• Vehicular trips The generation rates are
  vehicular trips for average vehicle occupancy
• Variability in rates variation in data
• Sample size Some have only a small number of
  samples

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Pass-by Traffic

• Land use activities such as offices, industrial
  parks, hotels, high-quality restaurants, and
  residential development generate traffic which
  intends to have a trip end at the particular site
  and therefore constitute new traffic on the
  street system.
• However, a sizable portion of the traffic
  generated by fast-food restaurants and gas
  stations is already on the adjacent street and
  merely stops at the establishment in passing by ?
  I.e. pass-by traffic. They are NOT new traffic.
  They were there but because a new establishment
  was developed, they just decided to make a detour.

See Table 3-4 for variation of the amount of
pass-by traffic by generator type and size, and
Table 3-5 for daily variation, and Table 3-6 for
weekly variation
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Mixed-use development

• When an activity center is developed with a mix
  of different land uses (e.g., retail and office),
  there are fewer trips on and off the site than if
  the retail and office activities are developed on
  separate sites. In a mixed-use development, some
  individuals will complete two or more purposes
  without leaving the site.

Shopping center
(See Table 3-7 and 3-8)
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Satellite development

• Regional shopping centers attract other
  commercial retail developments to property
  surrounding the center. The interaction (shared
  trips) may be 10 or more of the traffic
  generated by a satellite development. The number
  of shared trips will be subtracted when it is
  loaded to the external roadway. Note this is
  not a chained-trip. A chained trip is a trip that
  combines different trip purposes (work, shop,
  day-care drop off, etc.).