Impacts of Proxy Reporting in Household Surveys on Trip Rates Ed Hard | David Pearson 13th TRB Transportation Planning Applications Conference Reno, NV May 12, 2011

What We Did…. Analyzed difference in the number of trips reported by respondent, proxy, and diary Used data from 3 HH surveys All surveys used same methodology and instruments Person trips compared and evaluated by retrieval method

Evaluation of Person Trips Compiled and compared for respondent, proxy, and diary methods by Aggregate totals by urban area Per person by age cohort Per person by HH size and income Various categories of person and HH lifecycles HBW, HBNW, NHB by area and by age cohort, HH size and income, and lifecycle

Comparison of Person Trip Rates Calculated difference in rates to determine if statistically significant difference between Respondent and proxy Respondent and diary Proxy and diary Used test statistic

Summary of Findings Person trip rates for respondent 25 to 45 % higher than proxy; for diary 58-95% higher than proxy When stratified by age cohorts, rates for respondent and diary consistently higher than proxy No significant difference in male vs. female rates Significant under-reporting of adults represented by proxy

Comparison of Trip Rates by Retrieval Method RIO GRANDE VALLEY Comparison of Trip Rates by Retrieval Method AUSTIN AMARILLO

Summary of Findings Appears to be a tendency to over-report HBW trips and under-report HBNW and NHB Potential impact of this on TDMs and estimates of total travel is significant Trip rates essentially the same for the three areas for each method of data retrieval Implies raw survey data may be combined between urban areas and weighted to represent local conditions Analysis of Houston HH survey data reveals same general findings on person trip rates in relation to retrieval method

Comparison of Trip Rates by Purpose by Retrieval Method Results/Trends Similar for All Areas RIO GRANDE VALLEY RIO GRANDE VALLEY RIO GRANDE VALLEY

Recommendations For Texas Travel Survey Program Allow no more than 20 percent of individuals over age 15 to be represented by proxy Modify HH survey analyses to include development of adjustment rates by age cohort and purpose for proxy individuals Research to examine combining unweighted HH surveys from different areas to develop trip rates for areas without HH surveys

QUESTIONS Ed Hard (979) 845-8539 e-hard@tamu.edu David Pearson (979) 845-9933 d-pearson@tamu.edu