Empirical Analysis of Merging Behavior at Freeway On-Ramp

The ability of microscopic (simulation) models to represent lane-changing behavior according to reality has recently been questioned. In this paper the merging maneuver (a specific type of lane changing) is analyzed with empirical data. First, a conceptual model is composed; it includes the factors influencing merging behavior, namely the merge location and its relation to prevailing driving conditions, gap acceptance, and the relaxation phenomenon. The empirical data set consists of 35 min of vehicle maneuvers on 400 m of freeway, collected by a camera mounted underneath a helicopter. This process results in a data set of 3,459 vehicle trajectories, from which 704 trajectories describe merging vehicles. It is found that different merge locations are used under congested and freeflow traffic conditions. During free-flow, most vehicles merge at the first half of the acceleration lane. Under congested traffic conditions, relatively more merges are registered at the end of the acceleration lane. The smallest accepted gap observed in the data set lies between 0.75 and 1.0 s. Net headways between the merging vehicle and the new leader and new follower of less than 0.25 s are recorded. These short accepted gaps are growing over time and indicate relaxation behavior. From the data analysis it can be concluded that gap acceptance theories, as they are used in current models and theories to model merge behavior, are not able to model the observed behavior accurately.