Traffic Analysis - Trip Generation

8/12/2019 Traffic Analysis - Trip Generation

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Lec 26: Ch3.(T&LD): Traffic AnalysisTrip generation

Know the definition of site-oriented and non-site traffic

Understand the phases of site impact trafficevaluation (S.I.T.E.)

Learn how to estimate trips generated by adevelopment

Know how to use ITE Trip GenerationHandbook


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Site-oriented traffic vs. Non-site traffic

Without thedevelopment

With thedevelopment(new orexisting)

Site-orientedtraffic (tripshaving an ODon the site

Non-site traffic (noOD on the site)


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SITE Methodology

Phase I:Establish existing traffic conditionswithout the site (proposed)

Phase II:Forecast future traffic conditionswithout the site

Phase III:Forecast future site-only trafficconditions

Phase IV:Determine total future trafficconditions (II + III)

Phase V:Evaluate alternative improvements

Phase VI:Negotiations

Phase VII:Implementation


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Flow chart of SITE process

Existing BackgroundTraffic

CalculateLOS

Phase I

Phase IITraffic growthfactors

Input fromMPO andlocal/stateagencies

Future backgroundtraffic w/o site

Forecast trafficfor other newadjacent sites

Combine

CalculateLOS Compare


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Flow chart of SITE process (cont)

Forecast traffic for sitedevelopment

Phase III

Phase IVCombine

Total traffic

CalculateLOS

Compare


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Flow chart of SITE process (cont)

Develop alternativesolutions

Phase V

Phase VI

Begin negotiations betweenlocal officials and developers

Documentfindings

Evaluatesolutions

Feedback

Perform supplementaltechnical analyses

Feedback

Phase VII

Assist in preparingconstruction plans

Implementation


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Site-oriented traffic (site-generated trips): mucheasier to estimate because

The land use activities are known

The number of trips expected to be generated by theproposed development can be determined using the ITE TripGeneration 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 thepeak hours of the adjacent street

The number of trips to and from the site during thepeak(s) of the generator

Daily variation

Monthly variation

5 Primarycharacteristics


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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 peroccupied dwelling unit)

Be relatively easy to establish/measure (meaning easy tomeasure the size, like size of an household, size of a store)

Provide consistent and transferable rates (Althoughvariations exist, establishments of similar characteristics havesimilar trip generation rates.

(See the handout)


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Issues (pp. 29, 39, 40)

Age of data baseNot much difference between old and new data

Daily variationsPeaking of traffic varies depending on the type ofdevelopment

Location variationITE trip generation data came from suburban areas(for vehicular trips)

Pass-by trafficSome generators attract traffic from the passing trafficstream

Mixed-use developmentMixed-use land may produce less trips thanthe sum total of individual land uses (many rates are derived from stand-

alone developments)Vehicular tripsThe generation rates are vehicular trips for average

vehicle occupancy

Variability in ratesvariation in data

Sample sizeSome 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 residentialdevelopment generate traffic which intends to have a tripend at the particular site and therefore constitute newtraffic on the street system.

However, a sizable portion of the traffic generated byfast-food restaurants and gas stations is already on theadjacent street and merely stops at the establishment inpassing by I.e. pass-by traffic. They are NOT newtraffic. They were there but because a new establishmentwas developed, they just decided to make a detour.

See Table 3-4 for variation of theamount of pass-by traffic bygenerator 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 landuses (e.g., retail and office), there are fewer trips on and off thesite than if the retail and office activities are developed onseparate sites. In a mixed-use development, some individuals willcomplete two or more purposes without leaving the site.

(See Table 3-7 and 3-8)

Shopping center


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Satellite development

Regional shopping centers attract other commercial retaildevelopments to property surrounding the center. Theinteraction (shared trips) may be 10% or more of the trafficgenerated by a satellite development. The number ofshared trips will be subtracted when it is loaded to the

external roadway. Note: this is not a chained-trip. Achained trip is a trip that combines different trip purposes(work, shop, day-care drop off, etc.).

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Traffic Analysis - Trip Generation