Deviations in pedestrian itineraries in urban areas: a method to assess the role of environmental factors

Walking has long been neglected in urban-mobility research, but it is now making its way into numerous studies using various approaches. Empirical data are often processed in well-known models of flow allocation to study the behaviour of pedestrians and to identify their preferences. However, these models assume that route choices are predetermined at the start of each trip and do not admit any possible intervening decision along these trips. We propose to overcome this limitation through a new method for the analysis of pedestrian behaviour. This method, which we call 'deviation analysis' consists of (I) identifying the intersections from which a pedestrian has chosen a route longer than the shortest path; (2) defining the segments of the network which diverge from each deviation; (3) testing the influence of the environmental variables of these segments on the choice of route by using a discrete choice model. Deviations are compared with the cases where pedestrians follow the shortest path (called 'continuations), which are assumed to be less strongly linked to environmental variables due to the 'natural' choice for minimising the distance travelled. This method is applied to a series of pedestrian trips recorded in the French city of Lille. Results show that the environmental variables used in this study contribute to explaining the route choices with more strength when the deviations involve a trip lengthening of at least 50 m. They also show that the influence of variables describing the visual aspect of urban landscape may influence the route choices and outline the positive role of the urban atmosphere linked to the commercial function of streets.