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Paul St-Aubin added Methodology - Measurements - TTC.tex
almost 10 years ago
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\subsubsection{Time-to-collision}
\subsubsection{Post-encroachment time}
While TTC and motion prediction model collision potential, other surrogate safety measures aim to measure collision proximity from crossing, but not necesarily colliding movements. Trajectory data is detailed enough to provide gap acceptance time (GT) and post-encroachment times (PET). These are measures that broadly characterise how aggresively merging and crossing tasks are performed, respectively. As such, there is generally only one of these measures for the entire common time interval of a pair of road users.
For the crossing zone defined by the intersection of the two trajectories of a pair of road users, the post-ecnrochment time measure the time between complete departure of the first arriving vehicle, and first arrival of the last arriving vehicle. If PET < 0, a collision ensues. As such, higher PETs demonstrate safer behaviour.
Gap acceptance time similarly measures arrival and departure of a road user at a common crossing zone, but in this case, the crossing zone occurs inline during a merging task, usually followed by following behaviour.
