The understanding and the characterisation of individual mobility patterns in urban environments is important in order to improve liveability and planning of big cities. In relatively recent times, the availability of data regarding human movements have fostered the emergence of a new branch of social studies, with the aim to unveil and study those patterns thanks to data collected by means of geolocalisation technologies. In this paper we analyse a large dataset of GPS tracks of cars collected in Rome (Italy). Dividing the drivers in classes according to the number of trips they perform in a day, we show that the sequence of the travelled space connecting two consecutive stops shows a precise behaviour so that the shortest trips are performed at the middle of the sequence, when the longest occur at the beginning and at the end when drivers head back home. We show that this behaviour is consistent with the idea of an optimisation process in which the total travel time is minimised, under the effect of spatial constraints so that the starting points is on the border of the space in which the dynamics takes place.
