Editing Trip distribution (section)

=== Stability of travel times ===
A key point in analyzing feedback is the finding in earlier research<ref> Levinson, D. and A. Kumar 1994 The Rational Locator: Why Travel Times Have Remained Stable, Journal of the American Planning Association, 60:3 319&ndash;332</ref> that commuting times have remained stable over the past thirty years in the Washington Metropolitan Region, despite significant changes in household income, land use pattern, family structure, and labor force participation. Similar results have been found in the Twin Cities<ref>Barnes, G. and Davis, G. 2000. ''Understanding Urban Travel Demand: Problems, Solutions, and the Role of Forecasting'', University of Minnesota Center for Transportation Studies: Transportation and Regional Growth Study</ref>

The stability of travel times and distribution curves over the past three decades{{When|date=May 2016}} gives a good basis for the application of aggregate trip distribution models for relatively long term forecasting. This is not to suggest that there exists a constant [[Marchetti's constant|travel time budget]].