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Conducting a Trip Generation Study

Conducting a Trip Generation Study. When to Collect Data. Not covered by the ITE land use classification Location is in CBD Significant multi-modal component Size of site is not within ITE data range Insufficient sample size Inadequate statistical confidence

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Conducting a Trip Generation Study

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  1. Conducting a Trip Generation Study

  2. When to Collect Data • Not covered by the ITE land use classification • Location is in CBD • Significant multi-modal component • Size of site is not within ITE data range • Insufficient sample size • Inadequate statistical confidence • Inconsistent from sites included in existing database (age of res., worker shifts, diff. ind. Var.) • Multi-use development • Questioned by professionals or local officials

  3. Sample Size Determination • Establish local trip generation rateat least 3 sites preferably 5 • Validate ITE trip generation rateat least 3 sites • Combine local data with ITE dataat least 2 sites • Submit data to ITEat least on site

  4. Site Selection • Transferrable (dev. Size, development mix, location w/r to network and dev. Patterns) • At least 85% occupancyAt least 2 yrs old • Independent variable data available • Can isolate site for counting (no shared parking, no shared driveways, limited ped traffic from nearby, limited transit, no through traffic) • Security • Single land use activity • No construction • Owner permission

  5. Independent Variable Selection • Available • Variable size would affect trip generation • Should be accurate not estimated or derived • Currently used in manual

  6. Development Data Requirements • Site description • Square footage/units • Percent occupancy • Site acreage • Location (CBD, suburban, rural) • Name and description of principal use • Site plan • Adjacent street traffic volumes

  7. Survey Periods • Automatic count • 7-day period ideal • 1-day period at a minimum • 2-day preferable • Manual counts • 2-hours for each peak • Season • No-variation then pick average day • Variation then pick 30th or 50th highest hour • Time of survey should represent typical activity (good weather, no big sale, etc.)

  8. Conducting the Study • Directional volumes • 15-minute periods • Two or more days of peak period counts • Adjacent street hourly traffic counts for establishing peak period time • Concurrent counts • Site data from owners • Verify automatic counts with short-period manual counts • If needed, vehicle classification and vehicle occupancy

  9. Establishing a Local Trip Generation Rate of Equation • Hypothesis for why local conditions are unique • Confirm that local data justify local trip generation rate/equation • 3 sites (5 preferable) • Difference of average greater than +/- 15% • Local data consistent • Rate or equation satisfies statistical standards • For ave: • At least 3 data points • Std/ave <= 1.10 • For Equation: • At least 4 data points • R2 >=0.75

  10. Validation of Trip Generation Rates/Equations for Local Use • STEP 1: Collect data at 3 sites or more • STEP 2: Analysis of the local data, comparing to ITE • ITE data valid if… • Criteria 1: trip generation rate for local site within +/- std • Criteria 2: at least one site rate higher and one lower OR all with 15% • Criteria 3: local data generally fall within ITE scatter • Criteria 4: common sense • If all of the criteria of STEP 2 are not met then consider local rate or equation

  11. Combining Trip Generation and Local Data • Combine if ITE and local rates within 15% • Does not give precise std or regression equation • Sum trip ends(ITE) = weighted average * average X * number of studies • Sum independent variable units (ITE) = average X * number of studies

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