Norman W. Garrick CTUP

Norman W. Garrick Transportation Forecasting What is it? Transportation Forecasting is used to estimate the number of travelers or vehicles that will use a given transportation facility in the future The conventional approach to transportation forecasting is based on what is commonly know as the ‘four step model’

Norman W. Garrick The Four Step Model Trip Generation Estimates the number of trips from given origins and destinations Trip Distribution Determines the destination for each trip from a given origin Mode Choice Determines the mode choice for each trip Route Assignment Determines the specific route for each trip

Norman W. Garrick Trip Generation Trip Generation model is used to estimate the number of person-trips that will begin or end in a given traffic analysis zone The unit of analysis for traffic generation is the TAZ

Norman W. Garrick Trip Generation Model Calibrated Model Estimated Target year socio-economic, land use data Predicted Target year No. of Trips

Norman W. Garrick Trip Generation What is Predicted? Trip generation models predict so called TRIP ENDS for each zone The trip ends maybe classified as either ORIGINS and DESTINATIONS (O-D) or PRODUCTIONS and ATTRACTIONS The two sets of terms sound similar but there is a technical difference

Norman W. Garrick Origins and Destinations A worker leaves Zone 1 in the morning to go to work in Zone 8 This results in 2 trip ends: One Origin for Zone 1 One Destination for Zone Residential Non-residential Residential Non-residential When that same worker leaves Zone 8 in the evening to go to home to Zone 1 This results in another 2 trip ends: One Destination for Zone 1 One Origin for Zone 8 Total Number of Trip Ends Zone 1: 2 Trip Ends (1 O, 1 D) Zone 8: 2 Trip Ends (1 O, 1 D)

Norman W. Garrick Productions and Attractions A worker leaves Zone 1 in the morning to go to work in Zone 8 This results in 2 trip ends: One Production for Zone 1 One Attraction for Zone Residential Non-residential Residential Non-residential When that same worker leaves Zone 8 in the evening to go to home to Zone 1 This results in another 2 trip ends: One Production for Zone 1 One Attraction for Zone 8 Total Number of Trip Ends Zone 1: 2 Trip Ends (2 Productions) Zone 8: 2 Trip Ends (2 Attractions)

Norman W. Garrick Origins and Destinations?? Productions and Attractions?? Based on the convention of trip generation models Origins and Destinations are defined in terms of the direction of the trip Productions and Attractions are defined by the land use Residential Land use PRODUCES trip ends Non-residential land use ATTRACTS trip ends This is a useful distinction because of how trip generation models are typically developed

Norman W. Garrick Modeling Productions and Attractions Trip generation models typically model separately, i) residential trip production, ii) non- residential trip attractions 1 Non-residential Residential For example, Trip Ends for Zone 1 would be reported as Production Trip Ends Attraction Trip Ends This approach works for home based trips (HB). But falls apart when we start to consider non-home based trips (NHB). Special techniques are developed to deal with the relatively small number of NHB that occurs.

Norman W. Garrick Zonal Based Trip Generation Models Zonal Based Models use zonal averages to estimate trip making. One problem with this approach is that zonal averages may be deceptive depending on the distribution of a given parameter. For example, two zones with the same average income could have very different income distribution and presumable different travel performances. These models are referred to as AGGREGATE Models

Norman W. Garrick Household Based Trip Generation Models Household Based Models use the household as the unit for estimating trip making. The underlying assumption of household based models is the assumption that household with the same characteristics (for example, same number of adults and cars, and same income) tend to have the same travel tendencies As we have discussed, this assumption might or might not be true depending on the characteristic of the land use in which the household is located Based on this assumption average trip making is determined for each household category These models are called DISAGGREGATE Models

Norman W. Garrick Forms of Trip Generation Models Three Forms of Trip Generation Models are featured in the text 1.Regression Models A regression model is used to estimate the trip rate based on characteristics of the zone 2.Trip-Rate Analysis Trip rate is estimated on characteristics of the trip generators with in the zone. Production rates are determined using the characteristics of the residential land uses and attraction rates using the characteristics of the nonresidential land uses 3.Cross-classification Models This is a variation of the trip-rate analysis from above. The difference is that the trip generation models (for the residential land uses) are disaggregate models

Norman W. Garrick Trip Rate Analysis Trip-Rate Analysis Trip rate is estimated on characteristics of the trip generators with in the zone. Production rates are determined using the characteristics of the residential land uses and attraction rates using the characteristics of the nonresidential land uses Example from Text, Page 355, Table The characteristics of the trip generator is given in 1000 SQ. FT. And the trip generation rate for each generator is given as TRIPS PER 1000 SQ. FT. For example Residential: Total 1000 Sq. Ft. = sq. ft., Trip Gen. Rate = 2.4 trips/1000 sq.ft TOTAL NO. of TRIP from residential land use = 2744*2.4 = 6586 Trips