National Academies Press: OpenBook

A Guidebook for Using American Community Survey Data for Transportation Planning (2007)

Chapter: Appendix I - Comparison of ACS and Decennial Census Transportation Planning Estimates

« Previous: Appendix H - ACS Selected Population Profiles
Page 253
Suggested Citation:"Appendix I - Comparison of ACS and Decennial Census Transportation Planning Estimates." National Academies of Sciences, Engineering, and Medicine. 2007. A Guidebook for Using American Community Survey Data for Transportation Planning. Washington, DC: The National Academies Press. doi: 10.17226/13895.
×
Page 253
Page 254
Suggested Citation:"Appendix I - Comparison of ACS and Decennial Census Transportation Planning Estimates." National Academies of Sciences, Engineering, and Medicine. 2007. A Guidebook for Using American Community Survey Data for Transportation Planning. Washington, DC: The National Academies Press. doi: 10.17226/13895.
×
Page 254
Page 255
Suggested Citation:"Appendix I - Comparison of ACS and Decennial Census Transportation Planning Estimates." National Academies of Sciences, Engineering, and Medicine. 2007. A Guidebook for Using American Community Survey Data for Transportation Planning. Washington, DC: The National Academies Press. doi: 10.17226/13895.
×
Page 255
Page 256
Suggested Citation:"Appendix I - Comparison of ACS and Decennial Census Transportation Planning Estimates." National Academies of Sciences, Engineering, and Medicine. 2007. A Guidebook for Using American Community Survey Data for Transportation Planning. Washington, DC: The National Academies Press. doi: 10.17226/13895.
×
Page 256
Page 257
Suggested Citation:"Appendix I - Comparison of ACS and Decennial Census Transportation Planning Estimates." National Academies of Sciences, Engineering, and Medicine. 2007. A Guidebook for Using American Community Survey Data for Transportation Planning. Washington, DC: The National Academies Press. doi: 10.17226/13895.
×
Page 257
Page 258
Suggested Citation:"Appendix I - Comparison of ACS and Decennial Census Transportation Planning Estimates." National Academies of Sciences, Engineering, and Medicine. 2007. A Guidebook for Using American Community Survey Data for Transportation Planning. Washington, DC: The National Academies Press. doi: 10.17226/13895.
×
Page 258
Page 259
Suggested Citation:"Appendix I - Comparison of ACS and Decennial Census Transportation Planning Estimates." National Academies of Sciences, Engineering, and Medicine. 2007. A Guidebook for Using American Community Survey Data for Transportation Planning. Washington, DC: The National Academies Press. doi: 10.17226/13895.
×
Page 259
Page 260
Suggested Citation:"Appendix I - Comparison of ACS and Decennial Census Transportation Planning Estimates." National Academies of Sciences, Engineering, and Medicine. 2007. A Guidebook for Using American Community Survey Data for Transportation Planning. Washington, DC: The National Academies Press. doi: 10.17226/13895.
×
Page 260
Page 261
Suggested Citation:"Appendix I - Comparison of ACS and Decennial Census Transportation Planning Estimates." National Academies of Sciences, Engineering, and Medicine. 2007. A Guidebook for Using American Community Survey Data for Transportation Planning. Washington, DC: The National Academies Press. doi: 10.17226/13895.
×
Page 261
Page 262
Suggested Citation:"Appendix I - Comparison of ACS and Decennial Census Transportation Planning Estimates." National Academies of Sciences, Engineering, and Medicine. 2007. A Guidebook for Using American Community Survey Data for Transportation Planning. Washington, DC: The National Academies Press. doi: 10.17226/13895.
×
Page 262

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

We evaluated the general quality and validity of three-year accumulations (1999–2001) of ACS residence-, workplace-, and flow-based transportation-related data for nine test counties by comparing them to Census 2000 data that correspond to CTPP Part 1, Part 2, and Part 3 data. The ACS and Census data tables were provided to the project team by FHWA, who had received them for evaluation from the Census Bureau. This appendix summarizes the analyses that were conducted. The database included tract-level tabulations for nine counties and transportation analysis zone (TAZ)-level tabulations for the five counties for which TAZ data had been specified. Table I.1 shows the geographic areas covered. The comparison tables that were provided included those CTPP-type tables that are listed in Tables I.2, I.3, and I.4 for the residence-, workplace-, and flow-based estimates. Residence-Based Evaluation For the residence-based estimates, we computed the differences in estimates between the ACS and CTPP, tried to identify statistically significant differences, and looked for factors that might contribute to those differences through regression analysis. The estimates available in the Part 1 datasets are counts (e.g., number of people/house- holds/housing units with a certain characteristic). To compare the estimates, we converted the individual table cell estimates to percentages of the table totals. This means that differences due to slightly different weighted populations were accounted for. We then graphically examined the differences in the percentages between the CTPP data and ACS data at the tract and TAZ levels. For the most part, the two datasets appear to show the same patterns for the transportation- related tables. Only a small number of tracts and TAZs show significant variance between the two datasets. However, it should be noted that for some tracts and for many TAZs, ACS sample sizes were too small to show values. Next, we tested the significance of the observed differences. The standard errors of the ACS esti- mates were calculated by the Census Bureau and provided in the datasets used for this analysis. Since the CTPP standard errors were unavailable, we computed them using the methods described in the SF3 documentation, Section 8, “Accuracy of the Data.” For the purpose of statistical signif- icance testing, the difference in estimates is defined as the ACS count minus the CTPP count (note that for several of the tables provided, the ACS and CTPP estimates are means and medians). It is difficult to find any statistically significant differences at the 95 percent level of confi- dence, especially for smaller geographies. Examining those standard errors further, we note that 253 A P P E N D I X I Comparison of ACS and Decennial Census Transportation Planning Estimates

in most cases the ACS standard errors are much higher than the CTPP standard errors, ren- dering the t-statistic of the difference small enough as to be statistically insignificant. Figures I.1 through I.9 show the ACS and CTPP 95 percent confidence intervals for randomly selected tracts within each test county for an example variable. Note that the ACS confidence intervals are in general much wider than the CTPP confidence intervals because of the larger ACS stan- dard errors. The estimates for the variables appear to be largely in line with one another, but the sampling error for the three-year ACS data is too large to allow us to statistically confirm that this is the case or to determine if certain variables are more prone to be different. Although it was difficult to draw any meaningful conclusions about the statistical significance of the differences in estimates, we could examine the data to see whether the estimate differences were correlated with other tract characteristics. If this were the case, future comparisons between ACS and year 2000 CTPP data would be biased. We modeled these differences as a function of various population and household character- istics to check whether any particular variable is likely to bias the ACS estimates. We tested for the presence of systematic biases through regression analysis. For population estimates, we regressed the difference between the ACS and CTPP percentages as a function of the following population characteristics: • Total tract population, • Percent of population that are non-Hispanic white, • Percent of population that are Hispanic, • Percent of population that are 75 years or older, • Percent of population without a high school diploma, • Percent of population with an income below poverty line, and • Percent of workers in households with a disability. For household estimates, we regressed the difference between the ACS and CTPP percentages as a function of the following household characteristics: • Total households, • Percent of householders that are non-Hispanic, • Percent of householders that are Hispanic, • Percent of householders that are 75 years or older, • Percent of households with six or more people, • Percent of households with income below poverty line, and • Percent of households with single female head and kids. 254 A Guidebook for Using American Community Survey Data for Transportation Planning County Census Tract-Level Data Census TAZ-Level Data Pima County, Arizona San Francisco County, California Broward County, Florida Lake County, Illinois Hampden County, Massachusetts Douglas County, Nebraska Franklin County, Ohio Multnomah County, Oregon Bronx County, New York Source: Federal Highway Administration, 2004. Table I.1. Geographic areas represented in evaluation dataset.

Comparison of ACS and Decennial Census Transportation Planning Estimates 255 Table Universe Content 1 Total Population 2 Number of People Sampled 3 Sex by Age 4 All persons Hispanic Origin by Race 5 Persons 16 and over Employment Status 6 Total Workers 7 Mode to Work 8 Travel Time to Work 9 Time Leaving Home for Work 11 Household Income 12 Disability Status 13 Poverty Status 14 Disability Status by Mode to Work 15 Industry 16 Mode to Work by Time Leaving Home for Work 17 Mode to work by Travel Time to Work 18 Hispanic Origin 19 Hispanic Origin by Race 20 Hispanic Origin by Race by Mode to Work 21 Number of Workers in Household 22 Means of Transportation 23 Median Travel Time by Mode to Work 24 Mean travel Time by Mode to Work 26 Workers in households Average Number of Workers per Vehicles 28 Vehicles Available 29 Tenure 30 Number of Persons in Household 31 Number of Persons in Household by Number of Workers in Household 32 Number of Persons in Household by Vehicles Available 33 Number of Persons in Household by Household Income 34 Number of Workers in Household by Vehicles Available 35 Number of Workers in Household by Household Income 36 Telephone Availability 37 Number of Workers in Household by Vehicles Available by Household Income 38 Mean Household Income 39 Households Median Household Income 40 Aggregate Number of Vehicles 41 Total Housing Units 42 Number of Housing Units Sampled 43 Percent of Housing Units Sampled 44 Quarter 45 Housing units Occupancy Status Source: Federal Highway Administration, 2004. Table I.2. Residence-based evaluation dataset tables.

256 A Guidebook for Using American Community Survey Data for Transportation Planning Table Universe Content 1 Time of arrival at work 2 Worker earnings by Mode to work 3 Mode to work by Time of arrival at work 4 Mode to work by Travel time to work 5 Hispanic origin by Race by mode to work 6 Household income 7 Household income by Mode to work 8 Vehicles available by Mode to work 9 Median earnings by Mode to work 10 Mean earnings by Mode to work 12 Aggregate number of vehicles by Time Leaving Home for Work 13 Average Number of workers per vehicles by Time Leaving Home for Work 14 Number of workers per carpool by Time Leaving Home for Work 15 Median travel time by Mode to work 16 Mean travel time by Mode to work 17 Mean travel time by Mode to work 18 Mode to Work 19 Median travel time by Mode to work by Time arriving at work 20 Workers in Households Mean travel time by Mode to work by Time arriving at work 22 Aggregate number of carpools by Time Leaving Home for Work Source: Federal Highway Administration, 2004. Table I.3. Workplace-based evaluation dataset tables. 1 2 3 4 5 6 7 8 9 10 11 Table Universe Content Total Workers Vehicles Available per Household by Mode to work Means of Transportation Household Income by Means of Transportation Mean Travel Time by mode to work by Time Leaving Home Median Travel Time by mode to work and Time Leaving Home Aggregate Number of Vehicles by Time Leaving Home for Work Average Number of Workers per Vehicle by Time Leaving Home Aggregate Number of Carpools by Time Leaving Home for Work Number of Workers per Carpool by Time Leaving Home for Work Workers in Households Aggregate travel time by mode to work and Time Leaving Home Source: Federal Highway Administration, 2004. Table I.4. Flow-based evaluation dataset tables. The results of this analysis would answer questions such as: does the presence of minorities, low-income populations, or hard-to-reach communities in a certain area systematically bias the ACS estimates for that area? Would the ACS estimates be systematically larger or smaller than the CTPP estimates in seasonal areas? The regressions are ordinary least squares regressions that were estimated for most of the population and household variables listed in Table I.2. The analy- sis was done at the tract level. Systematic biases were measured to varying degrees in each of the Part 1 tables. For cer- tain tables, the bias is structural and is likely to be related to the differences in the survey instruments. For other tables, the measured differences seem to be related to sample size and would decrease as sample size increases. The residence-based tables with relatively large biases were • Disability status, • Disability status by mode to work,

Comparison of ACS and Decennial Census Transportation Planning Estimates 257 0 1,000 2,000 3,000 4,000 5,000 6,000 AC S- 00 02 00 CT PP -0 00 20 0 AC S- 00 12 00 CT PP -0 01 20 0 AC S- 00 21 00 CT PP -0 02 10 0 AC S- 00 26 02 CT PP -0 02 60 2 AC S- 00 30 02 CT PP -0 03 00 2 AC S- 00 35 04 CT PP -0 03 50 4 AC S- 00 39 03 CT PP -0 03 90 3 AC S- 00 40 30 CT PP -0 04 03 0 AC S- 00 40 40 CT PP -0 04 04 0 AC S- 00 40 50 CT PP -0 04 05 0 AC S- 00 40 60 CT PP -0 04 06 0 AC S- 00 41 12 CT PP -0 04 11 2 AC S- 00 43 18 CT PP -0 04 31 8 AC S- 00 44 12 CT PP -0 04 41 2 AC S- 00 45 05 CT PP -0 04 50 5 AC S- 00 46 16 CT PP -0 04 61 6 AC S- 00 46 26 CT PP -0 04 62 6 AC S- 00 46 36 CT PP -0 04 63 6 AC S- 00 47 15 CT PP -0 04 71 5 AC S- 00 49 00 CT PP -0 04 90 0 Tract Number N um be r o f W or ke rs High Estimate Low Figure I.1. Estimate of Workers Driving Alone-95 Percent Confidence Intervals (Pima County, Arizona). ACS versus CTPP for Selected Tracts AC S- 01 01 00 CT PP -0 10 10 0 AC S- 01 09 00 CT PP -0 10 90 0 AC S- 01 18 00 CT PP -0 11 80 0 AC S- 01 26 00 CT PP -0 12 60 0 AC S- 01 34 00 CT PP -0 13 40 0 AC S- 01 57 00 CT PP -0 15 70 0 AC S- 01 65 00 CT PP -0 16 50 0 AC S- 01 76 02 CT PP -0 17 60 2 AC S- 02 03 00 CT PP -0 20 30 0 AC S- 02 11 00 CT PP -0 21 10 0 AC S- 02 26 00 CT PP -0 22 60 0 AC S- 02 29 02 CT PP -0 22 90 2 AC S- 02 32 00 CT PP -0 23 20 0 AC S- 02 54 03 CT PP -0 25 40 3 AC S- 02 60 03 CT PP -0 26 00 3 AC S- 02 64 02 CT PP -0 26 40 2 AC S- 03 11 00 CT PP -0 31 10 0 AC S- 03 30 00 CT PP -0 33 00 0 AC S- 03 54 00 CT PP -0 35 40 0 AC S- 06 10 00 CT PP -0 61 00 0 Tract Number High Estimate Low 0 1,000 2,000 3,000 4,000 5,000 6,000 N um be r o f W or ke rs Figure I.2. Estimate of Workers Driving Alone-95 Percent Confidence Intervals (San Francisco County, California). ACS versus CTPP for Selected Tracts

258 A Guidebook for Using American Community Survey Data for Transportation Planning AC S- 86 03 02 CT PP -8 60 30 2 AC S- 86 08 06 CT PP -8 60 80 6 AC S- 86 09 04 CT PP -8 60 90 4 AC S- 86 10 11 CT PP -8 61 01 1 AC S- 86 12 01 CT PP -8 61 20 1 AC S- 86 14 04 CT PP -8 61 40 4 AC S- 86 15 10 CT PP -8 61 51 0 AC S- 86 17 02 CT PP -8 61 70 2 AC S- 86 20 00 CT PP -8 62 00 0 AC S- 86 25 02 CT PP -8 62 50 2 AC S- 86 29 02 CT PP -8 62 90 2 AC S- 86 34 00 CT PP -8 63 40 0 AC S- 86 38 01 CT PP -8 63 80 1 AC S- 86 41 01 CT PP -8 64 10 1 AC S- 86 42 05 CT PP -8 64 20 5 AC S- 86 44 02 CT PP -8 64 40 2 AC S- 86 44 12 CT PP -8 64 41 2 AC S- 86 45 14 CT PP -8 64 51 4 AC S- 86 45 21 CT PP -8 64 52 1 AC S- 86 55 01 CT PP -8 65 50 1 Tract Number High Estimate Low 0 1,000 2,000 3,000 4,000 5,000 6,000 N um be r o f W or ke rs Figure I.4. Estimate of Workers Driving Alone-95 Percent Confidence Intervals (Lake County, Illinois). ACS versus CTPP for Selected Tracts AC S- 01 03 01 CT PP -0 10 30 1 AC S- 01 06 05 CT PP -0 10 60 5 AC S- 02 02 06 CT PP -0 20 20 6 AC S- 02 03 17 CT PP -0 20 31 7 AC S- 02 05 01 CT PP -0 20 50 1 AC S- 03 08 01 CT PP -0 30 80 1 AC S- 04 05 02 CT PP -0 40 50 2 AC S- 04 17 00 CT PP -0 41 70 0 AC S- 04 31 00 CT PP -0 43 10 0 AC S- 05 05 00 CT PP -0 50 50 0 AC S- 06 01 12 CT PP -0 60 11 2 AC S- 06 02 06 CT PP -0 60 20 6 AC S- 06 05 05 CT PP -0 60 50 5 AC S- 07 02 04 CT PP -0 70 20 4 AC S- 07 03 14 CT PP -0 70 31 4 AC S- 08 04 02 CT PP -0 80 40 2 AC S- 09 09 00 CT PP -0 90 90 0 AC S- 10 01 02 CT PP -1 00 10 2 AC S- 11 03 04 CT PP -1 10 30 4 AC S- 11 03 18 CT PP -1 10 31 8 Tract Number High Estimate Low 0 1,000 2,000 3,000 4,000 5,000 6,000 N um be r o f W or ke rs Figure I.3. Estimate of Workers Driving Alone-95 Percent Confidence Intervals (Broward County, Florida). ACS versus CTPP for Selected Tracts

Comparison of ACS and Decennial Census Transportation Planning Estimates 259 AC S- 80 01 00 CT PP -8 00 10 0 AC S- 80 05 00 CT PP -8 00 50 0 AC S- 80 11 01 CT PP -8 01 10 1 AC S- 80 14 02 CT PP -8 01 40 2 AC S- 80 16 02 CT PP -8 01 60 2 AC S- 80 18 00 CT PP -8 01 80 0 AC S- 80 23 00 CT PP -8 02 30 0 AC S- 81 01 00 CT PP -8 10 10 0 AC S- 81 04 12 CT PP -8 10 41 2 AC S- 81 06 02 CT PP -8 10 60 2 AC S- 81 08 00 CT PP -8 10 80 0 AC S- 81 11 02 CT PP -8 11 10 2 AC S- 81 15 00 CT PP -8 11 50 0 AC S- 81 20 00 CT PP -8 12 00 0 AC S- 81 24 01 CT PP -8 12 40 1 AC S- 81 27 02 CT PP -8 12 70 2 AC S- 81 30 00 CT PP -8 13 00 0 AC S- 81 32 06 CT PP -8 13 20 6 AC S- 81 34 03 CT PP -8 13 40 3 AC S- 81 37 00 CT PP -8 13 70 0 Tract Number High Estimate Low 0 1,000 2,000 3,000 4,000 5,000 6,000 N um be r o f W or ke rs Figure I.5. Estimate of Workers Driving Alone-95 Percent Confidence Intervals (Hampden County, Massachusetts). ACS versus CTPP for Selected Tracts AC S- 00 06 00 CT PP -0 00 60 0 AC S- 00 19 00 CT PP -0 01 90 0 AC S- 00 26 00 CT PP -0 02 60 0 AC S- 00 33 00 CT PP -0 03 30 0 AC S- 00 39 00 CT PP -0 03 90 0 AC S- 00 47 00 CT PP -0 04 70 0 AC S- 00 54 00 CT PP -0 05 40 0 AC S- 00 60 00 CT PP -0 06 00 0 AC S- 00 64 00 CT PP -0 06 40 0 AC S- 00 66 04 CT PP -0 06 60 4 AC S- 00 68 06 CT PP -0 06 80 6 AC S- 00 70 03 CT PP -0 07 00 3 AC S- 00 73 09 CT PP -0 07 30 9 AC S- 00 74 07 CT PP -0 07 40 7 AC S- 00 74 32 CT PP -0 07 43 2 AC S- 00 74 39 CT PP -0 07 43 9 AC S- 00 74 46 CT PP -0 07 44 6 AC S- 00 74 53 CT PP -0 07 45 3 AC S- 00 74 60 CT PP -0 07 46 0 AC S- 00 75 09 CT PP -0 07 50 9 Tract Number High Estimate Low 0 1,000 2,000 3,000 4,000 5,000 6,000 N um be r o f W or ke rs Figure I.6. Estimate of Workers Driving Alone-95 Percent Confidence Intervals (Douglas County, Nebraska). ACS versus CTPP for Selected Tracts

260 A Guidebook for Using American Community Survey Data for Transportation Planning AC S- 00 05 02 CT PP -0 00 50 2 AC S- 00 09 02 CT PP -0 00 90 2 AC S- 00 14 00 CT PP -0 01 40 0 AC S- 00 19 00 CT PP -0 01 90 0 AC S- 00 24 02 CT PP -0 02 40 2 AC S- 00 29 01 CT PP -0 02 90 1 AC S- 00 34 01 CT PP -0 03 40 1 AC S- 00 37 02 CT PP -0 03 70 2 AC S- 00 41 01 CT PP -0 04 10 1 AC S- 00 47 00 CT PP -0 04 70 0 AC S- 00 55 00 CT PP -0 05 50 0 AC S- 00 62 00 CT PP -0 06 20 0 AC S- 00 67 01 CT PP -0 06 70 1 AC S- 00 72 02 CT PP -0 07 20 2 AC S- 00 80 01 CT PP -0 08 00 1 AC S- 00 85 00 CT PP -0 08 50 0 AC S- 00 91 02 CT PP -0 09 10 2 AC S- 00 98 04 CT PP -0 09 80 4 AC S- 01 03 03 CT PP -0 10 30 3 AC S- 01 04 08 CT PP -0 10 40 8 Tract Number High Estimate Low 0 1,000 2,000 3,000 4,000 5,000 6,000 N um be r o f W or ke rs Figure I.8. Estimate of Workers Driving Alone-95 Percent Confidence Intervals (Multnomah County, Oregon). ACS versus CTPP for Selected Tracts AC S- 00 02 20 CT PP -0 00 22 0 AC S- 00 09 10 CT PP -0 00 91 0 AC S- 00 20 00 CT PP -0 02 00 0 AC S- 00 28 00 CT PP -0 02 80 0 AC S- 00 48 10 CT PP -0 04 81 0 AC S- 00 58 20 CT PP -0 05 82 0 AC S- 00 63 52 CT PP -0 06 35 2 AC S- 00 65 00 CT PP -0 06 50 0 AC S- 00 69 31 CT PP -0 06 93 1 AC S- 00 71 12 CT PP -0 07 11 2 AC S- 00 74 24 CT PP -0 07 42 4 AC S- 00 75 40 CT PP -0 07 54 0 AC S- 00 79 32 CT PP -0 07 93 2 AC S- 00 81 62 CT PP -0 08 16 2 AC S- 00 83 80 CT PP -0 08 38 0 AC S- 00 91 00 CT PP -0 09 10 0 AC S- 00 93 32 CT PP -0 09 33 2 AC S- 00 93 82 CT PP -0 09 38 2 AC S- 00 95 20 CT PP -0 09 52 0 AC S- 00 98 00 CT PP -0 09 80 0 Tract Number High Estimate Low 0 1,000 2,000 3,000 4,000 5,000 6,000 N um be r o f W or ke rs Figure I.7. Estimate of Workers Driving Alone-95 Percent Confidence Intervals (Franklin County, Ohio). ACS versus CTPP for Selected Tracts

Comparison of ACS and Decennial Census Transportation Planning Estimates 261 ACS versus CTPP for Selected Tracts AC S- 00 02 00 CT PP -0 00 20 0 AC S- 00 52 00 CT PP -0 05 20 0 AC S- 00 67 00 CT PP -0 06 70 0 AC S- 00 85 00 CT PP -0 08 50 0 AC S- 01 15 01 CT PP -0 11 50 1 AC S- 01 32 00 CT PP -0 13 20 0 AC S- 01 54 00 CT PP -0 15 40 0 AC S- 01 75 00 CT PP -0 17 50 0 AC S- 02 01 00 CT PP -0 20 10 0 AC S- 02 15 02 CT PP -0 21 50 2 AC S- 02 27 02 CT PP -0 22 70 2 AC S- 02 51 00 CT PP -0 25 10 0 AC S- 02 89 00 CT PP -0 28 90 0 AC S- 03 18 00 CT PP -0 31 80 0 AC S- 03 40 00 CT PP -0 34 00 0 AC S- 03 61 00 CT PP -0 36 10 0 AC S- 03 74 00 CT PP -0 37 40 0 AC S- 03 86 00 CT PP -0 38 60 0 AC S- 03 99 02 CT PP -0 39 90 2 AC S- 04 14 00 CT PP -0 41 40 0 Tract Number High Estimate Low 0 1,000 2,000 3,000 4,000 5,000 6,000 N um be r o f W or ke rs Figure I.9. Estimate of Workers Driving Alone-95 Percent Confidence Intervals (Bronx County, New York). • Tenure (owned with mortgage category), • Number of workers in household by vehicles available by household income, • Poverty status (category for incomes between 100 and less than 150 percent of poverty), and • Telephone availability. Workplace-Based Evaluation For the workplace-based estimates, the evaluation of the differences between ACS and Cen- sus place of work tables was complicated by: • The absence of the extended place of work allocation system for ACS, and • The difficulty of calculation of standard errors of place of work for Census 2000. Therefore, the evaluation of the workplace-based estimates was based on descriptive analysis of the difference between the ACS and Census estimates. We evaluated the following variables at the county and tract levels: mode to work, vehicles available by mode to work, mean travel time by mode to work, worker earnings, and mean earnings by mode to work. The general conclusions from the workplace-based evaluation are: • The differences in the estimates between ACS and Census tend to be larger as the geographic level becomes smaller due to the larger variances in the ACS estimates; and • Overall, the ACS estimates do not seem to be biased; the distributions of the differences between ACS and Census estimates are not skewed in a certain direction. However, the ACS estimates of the percentage of workers who carpooled to work and the ACS estimates of travel time to work seem to be consistently lower than the corresponding Census estimates on average.

262 A Guidebook for Using American Community Survey Data for Transportation Planning 05X1: Mean Travel Time 0 5 10 15 20 25 30 35 - 10 0 t o -50 - 50 to -2 5 - 25 to -1 5 - 15 to -1 0 - 10 to -5 - 5 t o 0 0 t o 5 5 t o 1 0 10 to 15 15 to 25 25 to 50 50 to 10 0 ACS estimate - Census estimate (minutes) Pe rc en ta ge o f T ra ct O -D P ai rs Figure I.10. Comparison of ACS and Census 2000 worker flow data for tracts in San Francisco County. Worker Flow-Based Evaluation The worker flow evaluation datasets did not allow for a meaningful comparison of the differ- ences between ACS and CTPP, because: • The test site data were only for isolated counties, so only the worker flows with both trip ends in the counties were available; and • The disclosure limitations placed on the ACS test data were probably different than will be employed for actual future releases of the data, so conclusions about the test data are not likely to be valid. Figure I.10 is representative of the comparisons that were conducted on the worker flow-based tables. In general, the pattern of differences for travel times by mode among the comparable origin-destination flows did not reveal systematic bias in one direction or the other.

Next: Appendix J - Seasonality Analyses Using ACS »
A Guidebook for Using American Community Survey Data for Transportation Planning Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

TRB's National Cooperative Highway Research Program (NCHRP) Report 588: A Guidebook for Using American Community Survey Data for Transportation Planning explores incorporating the U.S. Census Bureau's American Community Survey (ACS) data into the transportation planning processes at national, state, metropolitan, and local levels. The report examines ACS data and products and demonstrates their uses within a wide range of transportation planning applications.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!