RE: [CTPP] CTPP Part 1: Mean Travel Time Calculations

Brian, In the Part 1 data for Oregon and California, we are aware that Mean, Median, and Standard Deviation tables for travel time to work were calculated incorrectly, as mentioned by you. Census Bureau fixed the error before they mailed out the CDs for all other states. Census Bureau also sent an errata sheet go out with all the Part 1 packages - the errata sheets show some of the errors that were observed by us in the LAST minute. For Oregon, and California, the mean travel time tables will be re-done for the final version. Most of the other issues mentioned on the errata sheet are related to the CTPP Access Tool software, and those errors will be fixed too. Nanda Srinivasan -----Original Message----- From: Brian.J.GREGOR(a)odot.state.or.us [mailto:Brian.J.GREGOR@odot.state.or.us] Sent: Monday, September 29, 2003 4:53 PM To: ctpp-news(a)chrispy.net Subject: [CTPP] CTPP Mean Travel Time Calculations Please excuse me if this observation has already been posted to the list. The mean travel times to work by county (for Oregon) reported on the CTPP disk are less than the times reported on the Census Bureau web site (QuickFacts). The CTPP numbers can be reproduced by dividing aggregate travel times reported in the CTPP by all workers reported in the CTPP. The Quick Facts numbers can also be reproduced using the CTPP data using the numbers of workers who do not work at home. This has been the standard approach to calculating mean travel times (including the 1990 CTPP). Was it intentional for the 2000 CTPP to use all workers in the calculation? If so, users should be made aware that the 2000 CTPP mean travel time numbers are not comparable to the 1990 CTPP mean travel time numbers. Brian Gregor, P.E. Transportation Planning Analysis Unit Oregon Department of Transportation Brian.J.GREGOR(a)odot.state.or.us (503) 986-4120