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
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