Survey Data
Table 1 presents race/ethnicity, income, and travel mode distributions of the survey sample. It also compares the sample with the 2005 American Community Survey (ACS) data representing the general population in the Tarrant, Denton, Collin and Dallas counties for the Dallas area and Harris, Montgomery and Fort Bend counties for the Houston area.
The results show that the survey sample consists of a large proportion of white and high-income survey respondents as compared to the 2005 ACS population for the two areas. The distribution of travel mode is close to the 2005 ACS, with a slightly high proportion for the non-single occupancy vehicle (SOV) groups. Approximately 31 percent of Houston respondents and 43 percent of Dallas respondents were currently using a toll road.
Table 1: Comparison of Survey Sample and the 2005 ACS
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In order to more accurately represent the general population in each metropolitan area, weights were developed to adjust the survey sample for analysis of interest in managed lanes. Procedures for weighting the survey data include three major steps:
- create data weighting parameters according to census data;
- adjust the percentage of interest in managed lanes based on the weighting parameters created at step 1; and
- adjust scores for given reasons using the weighting parameters.
Data for carpool analysis were not weighted due to three reasons: (1) the sample size of carpoolers was too small to yield significant observations for carpool questions by race/ethnicity and income; (2) the carpool sample catches the population that is most likely to be affected by managed lane policies because middle- or high-income users are choice carpoolers; and (3) research on carpool decisions and formation of this specific population will provide useful information for managed lane policy-making.