Development of a Lifestyle Trip Generation Model for Volusia County, FL, USA

Institute of Transportation Engineers. ITE Journal, May 2004 by Diaz, Luis E, Neidhart, Mike

ALTHOUGH THE DEMOGRAPHIC CHARACTERISTICS OF VOLUSIA COUNTY, FL, USA, SHOW A SIGNIFICANT PROPORTION OF RETIRED PERSONS, USERS OF TRANSPORTATION DEMAND MODELS IN FLORIDA HAVE RECOGNIZED THAT THE STANDARD TRIP GENERATION MODEL OVERESTIMATES THE NUMBER OF WORK TRIPS MADE BY THESE HOUSEHOLDS.

INTRODUCTION

Urban transportation planning plays a major role in the decision-making process for future policies, plans and programs. This decision-making process relies heavily on travel demand forecasts, which involve predicting the impacts that various policies and transportation improvements, such as new highways or bus routes, will have on travel in an urban area.

The standard travel demand model employs a four-step process that includes trip generation, trip distribution, mode choice and traffic assignment. Although each step in the model is important, trip generation is the first and, in many respects, the most influential stage in simulating travel behavior. Due to the fact that trip generation is the first step, the development of inaccuracies at this stage is compounded in the remaining trip distribution, mode choice and traffic assignment phases.

In an effort to ensure quality input data for its trip generation model, the Volusia County, FL, USA, metropolitan planning organization (MPO) began an investigation into the assumptions used in its trip generation travel demand model.

The Florida Department of Transportation (FDOT) developed the Florida Standard Urban Transportation Modeling Structure (FSUTMS), which provides a standard trip generation model to be used in any urban area in Florida. This standard trip generation model predicts urban trip-making behavior by translating urban activity characteristics into numbers of person-trips. The model typically incorporates three attributes of land use: intensity, location and character.

Intensity determines the amount of activity in a given zone and usually is stated as the number of households or employees. Location suggests the spatial distribution of activities. Characteristics of land use subsequently are divided into nonresidential and residential. Nonresidential land use is characterized by the type of activity (such as industrial, commercial, or service employment); residential land use typically is defined by the type of dwelling unit (such as single-family, transient, or multi-family).

Trip-making characteristics usually are divided into family attributes and family assets. Family attributes are defined as characteristics (such as family size) that are not a direct result of economic or spatial factors. Family assets, on the other hand, are defined as the economic resources of a family (such as income or automobile ownership). The existing standard trip generation model relates trip-making behavior between family attributes and assets of household size and automobile ownership and assumes that households of similar size generate similar amounts of trips.

Users of the standard FSUTMS trip generation model have recognized that some of the characteristics of Florida-such as the large proportion of retired persons-are not sufficiently considered in the standard trip generation model. As a result, the standard model often overestimates the number of work trips for these households while underestimating trips for other purposes.

Therefore, modeling professionals have recommended that a lifestyle trip generation model be substituted for the standard trip generation model. Depending on the lifestyle of a community, multiple independent variables can be used to develop a lifestyle trip generation model. The lifestyle trip generation model proposed for Volusia County takes into account the following three household lifestyles: retired households, working households without children and working households with children.

This proposed enhancement would better reflect the demographic characteristics of Volusia County, where there is a significant proportion of retired persons. This feature details the process of developing the input data for a lifestyle trip generation model that could be applied to a standard four-step travel demand analysis procedure.

In an effort to rely less on statewide assumptions, the Volusia County MPO undertook an extensive household travel survey, jointly funded by FDOT, Volusia County and the Volusia County MPO. One of the major purposes of the Volusia County Travel Survey project was to collect information that would allow for a better understanding of the travel habits and patterns of residents within the urban area. The collected data helped characterize the demographics of households as well as the travel patterns of corresponding household members.

Although the household survey was designed to produce data to estimate parameters for the MPOs trip generation, trip distribution and mode split modules, this feature focuses on the development of a new trip generation model. This research project used statistical methods to ensure the best use of resources for the development of accurate transportation models.