One other point. The travel times in 1990 and 2000 had slightly different top codes. This
can affect direct comparisons and local research on effects would be welcome. The top
coding differences are covered in the "Electronic Guidebook" which was mentioned
on this list serve last week.
"Srinivasan, Nanda" wrote:
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
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.
Sent: Monday, September 29, 2003 4:53 PM
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
Federal Highway Administration
19900 Governors Drive
Olympia Fields, Illinois 60461
708-283-3534 (V) 708-574-8131 (cell)