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Enhancing Internal Trip Capture Estimation for Mixed-Use Developments (2011) / Chapter Skim
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Appendix F - Validation of Estimation Procedure
Pages 148-154

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From page 148...
... . The validation test compared four different estimation methods to determine which method produced the results closest to the cordon counts: • the estimator described in this report, • the estimator, but without the proximity adjustment, • the existing ITE estimation method, and • unadjusted ITE trip generation.
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From page 149...
... In Figure F-1, it is evident that for the A.M. peak hour inbound vehicle trips, the NCHRP estimation methods -- both with and without the proximity adjustment -- produce the best results for three of the five developments; the current ITE method is closest for one site and slightly better than the NCHRP method for another site.
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From page 150...
... Center Counted at cordon 488 219 281 532 Estimator output 525 189 342 461 13% 26% 32% 31% From survey No data No data No data No data Estimator/counted 1.08 0.86 1.22 0.87 Without proximity adjustment Estimator output Same Same 342 461 Same Same 32% 31% Estimator/counted Same Same 1.22 0.87 With ITE Trip Gen Handbook data Estimator output 617 271 385 502 No data No data 26% 33% Estimator/counted 1.26 1.24 1.37 0.94 Unadjusted ITE Trip Generation report 655 295 566 678 0% 0% 0% 0% Unadjusted/counted 1.34 1.35 2.01 1.27 Table F-2. Summary of estimator validation comparisons.
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From page 151...
... P.M. Development/data In Out In Out In Out In Out Mizner Center Counted at cordon 220 145 547 328 Estimator output 239 99 417 388 13% 25% 29% 35% From survey No data No data No data No data Estimator/counted 1.09 0.68 0.76 1.18 Without proximity adjustment Estimator output Same Same 412 383 Same Same 30% 35% Estimator/counted Same Same 0.75 1.17 With ITE Trip Gen Handbook data Estimator output 267 134 425 402 No data No data 27% 32% Estimator/counted 1.21 0.99 0.78 1.23 Unadjusted ITE Trip Generation report 272 137 613 585 0% 0% 0% 0% Unadjusted/counted 1.24 0.94 1.12 1.78 Boca del Mar With proximity adjustment Counted at cordon - - 2187 2-way Estimator output - - 915 895 - - 26% 28% From survey No data No data 7% 8% Estimator/counted - - 0.83 2-way Without proximity adjustment Estimator output - - 689 676 - - 44% 47% Estimator/counted - - 0.62 2-way With ITE Trip Gen Handbook data Estimator output - - 839 831 - - 33% 35% Estimator/counted - - 0.76 2-way Unadjusted ITE Trip Generation report - - 1241 1209 - - 0% 0% Unadjusted/counted - - 1.12 2-way Southern Village Counted at cordon - - 1336 2-way Estimator output - - 546 438 Additional trips for non MXD uses - - 97 290 Total estimated - - 645 731 - - 11% 13% From survey No data No data No data No data Estimator/counted - - 1.03 2-way Without proximity adjustment Estimator output - - 537 429 No data No data N/Aa N/Aa Additional trips for non MXD uses - - 97 290 Total estimated - - 637 722 Estimator/counted 1.01 2-way With ITE Trip Gen Handbook data Estimator output 574 466 - - 6% 8% Additional trips for non MXD uses - - 97 290 Total estimated - - 671 756 Estimator/counted 0.99 2-way Unadjusted ITE Trip Generation report 633 512 - - 0% 0% Additional trips for non MXD uses - - 97 290 Total estimated - - 730 802 Unadjusted/counted 1.15 2-way a Person trips not known for non-MXD uses Table F-2.
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From page 152...
... Clearly, by examining the figures and Table F-3, it is easy to determine that the raw trip generation greatly overestimates external vehicle trip generation for the validation sites. The existing ITE method is a major improvement from raw trip generation.
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From page 153...
... The standard deviations for the recommended method, both with and without proximity adjustment, are about 20 percent of the actual external inbound and outbound volumes. This is less than the variations in the raw ITE nondirectional trip generation rates for the component land uses.
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From page 154...
... Addition of several more could possibly provide the basis for confirming the value of the proximity adjustment. F-7 Recommended NCHRP Method Error Type Raw ITE Trip Generation Existing ITE Method With Proximity Adjustment No Proximity Adjustment Explanation Average error +55% +26% -4% 7% Average error for sum of all sites Absolute average error 55 28 17 17 Average magnitude of error per site Standard deviation 68 34 20 19 Expect two-thirds of site estimates within this error range Table F-3.
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Key Terms

  • estimator output
  • ite trip
  • proximity adjustment
  • unadjusted ite
  • ite method

  • generation report
  • recommended method
  • raw trip
  • trip gen
  • raw ite

  • existing ite
  • gen handbook
  • handbook data
  • data estimator
  • vehicle trip

  • current ite
  • proximity adjustments
  • percent internal
  • peak hour
  • southern village

  • atlantic station
  • del mar
  • independent site
  • internal trips
  • component land

  • boca raton
  • estimation procedure
  • standard deviations
  • nchrp method
  • center counted


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