I want to thank everyone who commented on my memo about the 2004 ACS Data Release dated September 9, 2005. Also, I would like to respond and clarify some of the points raised by my colleagues throughout the country. As you know, the issues I raised in my September 9th post are not new; they were raised two years ago in Washington, DC at the TRB Annual Conference and at the Census Data for Transportation Conference in Irvine, CA, May 2005. Ed Christopher asked for help from the list server and census folks who produced the 2004 population estimates and 2004 ACS estimates. We got help from some of the list servers. But I don’t think we are going to have any response from the census folk because their evaluation of the ACS data indicated conclusions similar to mine (see for example Census Report No. 5 on the results of ACS). They may argue that the quality of the ACS product depends on the methodology, assumptions, and resources available. I think they are doing their best to obtain quality data from a small and unrepresentative sample. The “Guide to Using the ACS” and the “NCHRP Project” are probably not going to change the quality of ACS data much, which results from the current ACS assumptions, sample size, and content. Elaine Murakami - I completely agree with you that it is better to compare ACS results to ACS results rather than Census 2000. I also agree with you that the 2005 data will be more accurate than ACS 2004. The problem is that neither ACS 2004 nor ACS 2005 data are acceptable for transportation planning, especially for variables with small values such as walk and transit modes. The margin of error in these mode estimates is very large due to sample size and other factors. Your table for Mercer County is correct. But I think it is better to compare Census 2000 with ACS 2000 (apples to apples). Also, your conclusions on mode characteristics seems to be reasonable. As you know, we need TAZ level data for our studies. The current ACS program will produce larger errors than those estimated at the county level. Of all the things that you outlined for alternatives to replace the ACS, I would say bring back the long-form. I know it is not easy to reverse the decision that was made by the CB two years ago. Although not perfect, the responses to the long-form will be more reliable because it will be conducted with the decennial census, which is respected by almost everyone in the country. I think that FHWA should take the lead in promoting this effort and tell the country that the ACS data are not acceptable for the transportation community since the margin of error is very large. I really don’t know the effective channels of communication to have the long-form back in Census 2010. But I think the ACS issues should be brought to the attention of decision makers within AASHTO, APTA, NARC, TRB, Public Data Users, 2010 Census Advisory Committee, AMPO, 2010 Census Advisory Committee, AMPO, House Subcommittee on the Census, and other organizations. Of course political pressure is always needed. The other options you outlined are not really alternatives to the long-form. Improvements to the ACS county program will help a little but won’t solve the problem. Large surveys similar to the surveys conducted in the 1950's and 1960's are out of the question. Only the CB could implement a survey on group quarters population. Including group quarters population will improve the ACS quality but won’t solve the major problems in ACS data due to sample size. Home-to-Work flows is not the only data item we obtain from the long-form. I don’t think the CB will be able to improve its county population estimates significantly within the available resources. More than 10 years ago, I raised this question of quality with the CB and was told “We are only preparing county estimates, not a census”. Yet they are now using the county estimates instead of the census counts. I completely agree with Patty Becker that including group quarters population “won’t solve the whole problem” and the average of 2003-2007 in New Orleans will not be good. Also, I agree with Patty that it is good to have one year data for places of 65,000 or more population and 3-year data sets for places of 20,000 or more. Unfortunately, the current ACS program is not expected to produce accurate data for such areas because of sample size and many other factors. Tom Marchwinski gave excellent reasons for the error in ACS products. He questions the validity of aggregating five years of data and calling it a five-year average. He indicated that opening a major transit service, gas prices, major land use development, etc., can skew the ACS results and introduce additional errors in the ACD data. Grey Lipton stated incorrectly that Mercer County population “declined by 11,000 during between the two surveys (about 9,000 if you use the 2000 census population)”. According to census population estimates, Mercer County population grew by 13,693 persons between July 2000 and July 2004. Also, his conclusion about the number of walkers and the sample error is erroneous because it is based on the wrong numbers. In summery, the errors in the county ACS data for 2000-2004 are very large and the data cannot be used for transportation planning. Like 2004, the error in the 2005 ACS (Full Nationwide Implementation) for areas 65,000 plus population is expected to be large because of many reasons, including the ACS sample is smaller than decennial census, does not include group quarters population, and is weighted to an estimated population rather than census counts. The CB cannot do much to improve the quality of ACS because of limited resources. In order to obtain quality data for transportation planning, we have no option but to bring back the census long-form and include it in Census 2010. Although not perfect, decennial census data are the best estimates for all the variables that we need for transportation studies, including population, households, car ownership, travel modes including carpools, employed person by place of residence and place of work, Journey-to-Work, income, and travel time by mode of travel. FHWA is up to the challenge because it has been a leader in this area for the past 50 years.