[CTPP] Question on trend in average commute time

The following question was referred to me for comment and help, and I don't recall seeing any discussion of this on the CTPP listserver. If you have any thoughts on this, I will pass them along to the questioner. Thanks in advance for any insight you may have. Ed Hillsman ______________________________________________________ Edward L. Hillsman, Ph.D. Washington State DOT TDM Lead Researcher Public Transportation/Rail tel 360.705.7887 310 Maple Park Avenue SE fax 360.705.6862 P.O. Box 47387 hillsme(a)wsdot.wa.gov Olympia, WA 98504-7387 USA My colleague and I have been analyzing 2000 Census data and 2002 ACS data on commuting patterns, here in King County, WA with comparisons across the nation. The average 2002 commute time to work, reported in ACS for King County, was 25.0 minutes, down 1.5 minutes (5.7%) in the two years since the 2000 Census. Several comparable cities / counties across the US reported a similar pattern. St Louis, Houston, Boston, Oakland, Atlanta, and Washington DC all showed significant declines in average commute times over the two year period (10% decline in Washington DC). San Diego and New York City declined slightly. Of the ten metro counties we examined, only Cook County (Chicago) went up (by 3.8%). Our question is: Is the widespread reduction in commute time a function of the nationwide recession and decreasing employment levels, differences in the statistical instruments used, or something else? It's hard to believe the recession alone shows up that profoundly in commute times. The ACS question appears to be worded the same as the decennial Census question, but of course the sample is much smaller. We used the midpoint of the range the ACS provides. Can anyone think of an intervening variable we may have overlooked? Thank you for any insight you can provide!