Phone: 304-523-7434
Fax: 304-529-7229
400 Third Avenue
P.O. Box 939
Huntington, West Virginia 25712
TRIP GENERATION
The objective of the trip generation phase is to forecast the number of the motorized persons-trips that will begin from or end in each Traffic Analysis Zone (TAZ) within the study area for a typical day of the target year. In this step of travel forecasting process, the socioeconomic data are used to estimate the number of daily motorized person trips within the study area (internal-internal ) and those with origins (external-internal) or destination (internal-external) outside the study area. The trip generation models used by KYOVA for forecasting were developed based on travel surveys done in 1971. The procedure used to develop them have been documented in the report, "HIAIATS Existing Demands Transportation Facilities and Development Factors" prepared in May, 1970 (reference 6). These models forecast HBW, HBNW and NHB motorized person trips from each TAZ. In addition, the truck trips and the external-internal trips can also be forecasted using separate models. These models depend on the socioeconomic variables that are maintained by KYOVA such as dwelling units, population, employment, labor force and elementary high school attendance (2000). The output of these models are the trips produced and attracted from each TAZ.
The terms production and attraction, on the hand, are not defined in terms of the directions of trips but in terms of the land use associated with each trip end. A trip production is defined as a trip end connected with a residential land use in a TAZ, and trip attraction is defined as trip end connected to a nonresidential land use in a TAZ. On the basis of these definitions, TAZ "I" has produced two trips and TAZ"J" has attracted two trips. This distinction is made because the zonal trip productions can be more easily estimated from socioeconomic characteristics of the zone's population and the related travel needs of the population for various purposes, whereas, the zonal trip attractions depend on the availability and intensity of nonresidential opportunities found within the zone.
Huntington Ironton Area transportation Study (HIATS) original trip generation models were developed in the late 1960's. The procedures used to develop them have been document in the report," Huntington Ashland Ironton Area Transportation Study Phase II Future Travel and Highway Needs" prepared in May 1971(reference 7). Productions and attractions were calculated by purpose from zonal trip generation.
KYOVA has developed a dBASE program that utilized the socioeconomic to calculate productions and attractions for each TAZ. These trip ends are calculated for the following trip purposes: HBW, HBNW, NHBW and External-Internal. KYOVA developed another dBASE program to balance the productions and attractions.
Trip Generation Regression Equations
PRODUCTION EQUATIONS
WRK PAM = -8.25 + 1.74 TOT LF
OTH PAM = 3.42 + 3.61 CARS
SCH PAM = 3.36 + 1.82 SCH EN
ATTRACTION EQUATIONS
WRK AAM = 7.58 + 1.77 TOT EM
OTH AAM = 65.10 + 10.58 RETAIL EM + 1.48 DU + 0.44 OTHER EM
SCH AAM = 7.08 + 1.50 TOT AT
TOT AAM = 224.18 + 9.18 RETAIL EM + 1.64 TOT AT + 2.10 OTHER EM
OTHER EQUATIONS
NHB AM = -14.68 + 4.70 RETAIL EM + 0.81 OTHER EM + 0.81 DU + 0.20 TOT AT
TRUCKS = 12.32 + 0.52 RETAIL EM + 0.23 OTHER EM + 0.28 DU
EXTERNAL = 31.93 + 1.19 RETAIL EM + 0.26 OTHER EM + 0.10 DU + 0.05TOTAL AT
Trip Generation Regression Equations Variable Definitions
| VARIABLE NAME | DEFINITIONS | |
| 1 | DU | Dwelling Units |
| 2 | CARS | Automobiles Garaged in the Zone of Residence |
| 3 | POP | Population |
| 4 | TOT LF | Total Resident Labor Force |
| 5 | TOT EN | Total Resident Students |
| 6 | SCH EN | Primary and Secondary Resident Students |
| 7 | TOT EM | Total Employment within Analysis Zone |
| 8 | TOT AT | Total School Attendance within Analysis Zone |
| 9 | SCH AT | Primary and Secondary Attendant Students |
| 10 | RETAIL EM | Retail Employment within Analysis Zone |
| 11 | OTHER EM | Non-retail Employment within Analysis Zone |
| 12 | WRK PAM | Work Trip Productions All Modes |
| 13 | OTH PAM | Non-work Trip Productions All Modes |
| 14 | SCH PAM | School Trip Productions All Modes |
| 15 | TOTAL PAM | Total Home-Based Productions All Modes |
| 16 | WRK AAM | Work Trip Attractions All Modes |
| 17 | OTH AAM | Non-work Trip Attractions All Modes |
| 18 | SCH AAM | School Trip Attractions All Modes |
| 19 | TOTAL AAM | Total Home-Based Attractions All Modes |
| 20 | NHB | Non-home Based Trips |
| 21 | EXTERNAL | External-Internal Trips |
| 22 | TRUCKS | Light and Heavy Truck Trips |
BALANCING TRIP PRODUCTION AND ATTRACTIONS
The last step in trip generation modeling is the balancing of regional trip production and attractions. The estimated total trips produced at the household level should be equal to the total trips attracted at the activity centers. Each trip must have two ends a production and an attraction . In reality, the estimation of trip productions and attractions using the models will not the estimation of trip productions and attractions using the models will not be exactly equal. While trip production and attraction rates may contribute to the imbalance, the majority of the difference can be explained by estimation of the number of households socioeconomic characteristics of households, number of employees by type, and school attendance . To bring the regional totals into balance, the zonal attractions are scaled to equal regional trip production control totals. Control totals are set equal to the trip productions because we generally have a greater degree of confidence in household data than we do in employment data. This is particularly true when the 100% decennial census data are used to develop the number of households by zone.
Regional control totals were calculated to balance productions and attractions. This was done for each trip purpose HBW, HBO, and NHB. Regional productions and attractions consist of productions and attractions from traffic analysis zones, and productions and attractions from external stations. Productions and attractions at external stations are a function of observed and forecasted traffic volumes at the stations, and are considered fixed and are therefore not factored. Productions and attractions at external stations will not be balanced across zonal trips. Zonal trips include I-I, I-E, and E-I trips ends. The following equation is used to obtain the control total of trip productions:
CTp = Pz +Pe -Ae
Where
Ctp = control total of productions
Pz =control productions for each zone
Pe = trip productions at each external station, and
Ae =Trip attraction at each external station
Control totals are computer for each trip purpose. The next step is to compute the balancing factor for each trip purpose, using the following equation:
F = CTp / Az
where:
F= balancing factor (computed for each purpose)
Az= trip attractions at each zone
Each internal zone's trip attractions are then multiplied by balancing factor (by purpose) to arrive at the final balanced trip attractions. External station attractions are not factored.
A final summation of productions and attractions by purpose for all zones and external stations should be made, and they should be equal.
