Turbulence in traffic at motorway ramps and its impact on traffic operations and safety

In the vicinity of motorway ramps, multiple manoeuvres are performed by drivers that are entering or exiting the motorway, and by drivers that anticipate on, or cooperate with, the other entering and exiting vehicles. These manoeuvres involve lane-changes, changes in speed, and changes in headways. This results in changes in lane flow distribution, greater speed variability and changes in headway distribution on the different lanes, with presumably a greater share of small gaps on the outside lane. In literature and motorway design guidelines, this phenomenon is referred to as turbulence. Currently, an explicit definition for turbulence is unavailable. In this thesis, therefore, an explicit definition for turbulence is introduced: “individual changes in speed, headways, and lanes (i.e. lane-changes) in a certain road segment, regardless of the cause of change”. Turbulence is expected to be present in the traffic stream at any given time, and therefore a second definition is introduced: the level of turbulence, which is defined as: “the frequency and intensity of individual changes in speed, headways and lane-changes in a certain road segment, over a certain period of time”...SWOV-Dissertatiereeks SWOV – Instituut voor Wetenschappelijk Onderzoek VerkeersveiligheidTransport and Plannin