deletions | additions       diff --git a/subsection_Merging_Zone_The_reasoning__.tex b/subsection_Merging_Zone_The_reasoning__.tex  index 999ff97..1b68034 100644  --- a/subsection_Merging_Zone_The_reasoning__.tex  +++ b/subsection_Merging_Zone_The_reasoning__.tex 
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Speed and yPET are measured directly from the road user trajectories as they occur. TTC, however, requires the modeling of potential collisions. Typically, potential collisions are defined as collision courses of constant velocity, i.e. ``with movement remaining unchanged'' \citep{Amundsen_1977}. Given the non-linear environment of roundabouts, a more sophisticated motion prediction collision course model is used instead. For this work, the discretised motion pattern developped specifically as a result of motion prediction needs in roundabouts \citep{St_Aubin_2014} is used. It is be no means specific to roundabouts however.  Speed is widely regarded in the literature as a predictor of collision severity \citep[e.g.][]{Fildes_1993, elvik2004speed}. Meanwhile, TTC is one of the most popular surrogate safety measuresin the literature  intended as a predictor of collision probability (as it models near-misses). yPET is of interest as a model of yielding behaviour and merging aggressivity (it is related to gap time and gap acceptance).\subsection{Beahavoural Measures}