Un usuario para el nuevo ecosistema de la información

Five different data sources are incorporated in the study as summarized in Table 4.1. The 2007 HGAC Regional Household Activity and Travel Survey data was provided by the Texas Department of Transportation (TxDOT) and the Texas Transportation Institute (TTI). Other data were obtained from the HGAC, the regional association of local governments in the Gulf Coast Planning region of Texas.

Table 4.1 Data Sources and Applications.

Data Source Applied Measures Characteristics 2007 HGAC

Regional Household Activity and Travel Survey

- Travel outcomes: trip mode, trip frequency and VMT

- Vehicle information: travel cost

- 84% initially planned total samples for the HGAC survey area

- 54,672 trips in 61,731 trip records obtained from 4,775 sampled households

- 47,834 trips from 4,367 households collected for 6 counties in total 2007 Land Use

- Parcel-based GIS data prepared by County Appraisal District

- 2,074,341 parcels in 6,732 square miles in 6 counties

- Travel time, distance and transit fare

- Available for travel modes and time of day between TAZs 2008 Population

and Employment Forecasts

- Population and employment density

- Forecasts by many spatial units such as city, zip code and census tract

- Available from 2005 to 2040 on a yearly basis

2007 STAR Map - Design measures: connectivity and road length per 1,000 ft²

- Trademark for the Southeast Texas Addressing and Referencing Map - Including addresses, street name

and types and spatial information

First of all, the HGAC Regional Household Activity and Travel Survey intended to obtain the information on both individual and household travel characteristics in the metropolitan region. The survey was conducted for conventional 8 counties of the HGAC region including Brazoria, Chamber, Fort Bend, Galveston, Harris, Liberty, Montgomery and Waller counties. The random stratified household sampling method was introduced for the survey. The survey implementation was composed of three stages. First, randomly selected households were asked to participate in the survey by

telephone. If they agree, a packet of household activity and travel diary was sent to the household via mail. When the survey was collected after it was recorded for all household members, the survey data were retrieved by telephone.

Overall, four types of information were collected from the survey: household and individual characteristics, the information on vehicles owned by each household, and the information on every trip and activity made by each individual over 5 years old. The number of sampled households required for the HGAC survey area was 5,700 in total, which were randomly stratified by household size, the number of workers and household income. Due to incomplete survey at the time of the study, the information on 4,775 households (84%), 13,893 people and 54,672 trips was collected. Table 4.2 presents how the survey data has been processed while taking the study area and objectives, and trip purposes into consideration. Two datasets are finally prepared for different travel models. One is for individual mode choice models for 6,239 HBW trips and 10,413 HBO trips. Another dataset is prepared for both household trip generation and VMT models. They are estimated for 6,156 HBW trips by 2,539 households, 14,305 HBO trips by 3,461 households, and 29,858 total trips by 3,976 households.

Note in Table 4.2 that the number of trips and households are different between the mode choice models and other household travel models. The mode choice models are estimated only for HBW and HBO trips. They include return trips to home whose modes are not optional but significantly depend on the mode choice of departure trips from home. In terms of the theory of economic behavior, the inclusion of return trips results in biased estimation therefore, they are all removed from the final datasets. Many

distinct trip purposes are included in the HBO trips including school, pick-up and drop-off, personal, social and recreation, and shopping. The study pays main attention to personal, social and recreation and shopping trips because other trips are required for specific times at specific locations which are not appropriate for the study objectives.

Table 4.2 Result of Processing the Travel Survey Data for the Study Area.

Surveyed Data Arranged Data Studied Data Trip Purpose

Trips Households Trips Households Trips Households Total trips 47,834 4,367 42,275 4,170 29,729 Note: 1) Home-based work (HBW); home-based other (HBO), and non-home based (NHB)

trips.

2) Values are related to automobile modes (driving-alone and shared-ride). They are used in the household automobile trip generation model and household VMT model.

3) NHB trips are not analyzed in this study. So studied data are same as arranged data.

The 2007 land use GIS data which are made up of lots of parcels was obtained from the HGAC. The parcel-based land use GIS data has been prepared by each county appraisal distract for assessing property tax. They have been incorporated by the HGAC on a yearly basis, and used for forecasting socio-demographic data and providing regional GIS services. For 6 counties of the study area, over 2 million parcels in 6,729 square miles of total area are available. They are classified into 66 specific land use types along with specific spatial information. The data is useful for measuring dimensions of land use characteristics within specific boundaries.

Travel time and distance data extracted from the 2007 HGAC regional travel model were also obtained from the HGAC. The datasets were introduced to compute travel time and automobile operating cost between each pair of 2829 TAZs by different travel modes.The 2008 population and employment forecast data were downloaded from the HGAC website (HGAC 2009b). The number of population, employment and households were estimated in different spatial levels including counties, TAZs and census tracts. TAZ-level forecast data was used to measure the population and employment density in a quarter-mile boundary of every trip end. In addition, the 2007 STAR Map in GIS format was employed to measure land use design variables. It contains over 1.7 million address points, roadways, street names and types and other information (HGAC 2009c).

4.2 Variable Measurement