1. Lec 26: Ch3.(T&LD): 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

3. “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

4. 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
Evaluate solutions
Document findings
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

7. 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
5 Primary characteristics
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

8. 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)

9. 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

10. 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

11. 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)

12. 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.).