The paper concerns the travel activities and more specifically the urban travel time during a day. The daily TTB has been hypothesized by Zahavi (1980) as constant amount of time. First, the cities sprawl can easily be interpreted as a consequence of the increase in available speeds. And recently, Schafer and Victor (2000) have used the constant TTB concept to predict the future mobility of the world population. However, numerous critiques exist. The temporal and spatial dimensions of the stability are questioned and the apparent stability observed at aggregate levels may mask considerable variations at finer scale.Escaping unidimensional analysis limits and linear regression irrelevancy, the duration model incorporates impacts of covariates on the duration variable and permits to test the dependence of TTB on elapsed time. We apply the duration model to the TTB of Lyons (France), in the perspective of a discussion of Zahavi's hypothesis. The duration dependence estimation illustrates covariates effect on TTB and suggests a non-monotone hazard for their distribution, which conflicts with the TTB stability hypothesis and more generally with the classic travel time minimisation problem.
