Conflict Severity (CS)¶
Description¶
CS is concerned with solely estimating the severity of a potential collision in a scenario [Bagdadi2013]. It thus presents as a suitable factor that can enhance various collision probability metrics in ensuring a more accurate representation of criticality. From the perspective of an actor \(A_1\) performing a braking maneuver at time \(t_\mathit{evasive}\), it is defined as
Thus, it compares the (extended) \(\Delta v\) at time of the evasive maneuver against the \(\Delta v\) at the potential collision point as predicted by TTA if \(A_1\) conducts an emergency braking, assuming \(v_2(t_\mathit{evasive} + \mathit{TTA}(A_1, A_2)) = 0\). CS factors in the relative mass difference due to the correlation between severe injuries and fatality outcome, measured on the Abbreviated Injury Scale, and the mass ratio of the involved actors [Evans1994].
Properties¶
Run-time capability¶
No, as TTA can only be computed once evasive maneuver has been identified
Target values¶
Case study on manually labeled critical scenarios identified a mean CS of \(3.19 \pm 3.7\) m/s, but severity is dependent on speed and type of actors [Bagdadi2013]
Subject type¶
Any two actors, also suitable for VRUs
Scenario type¶
Any scenario for which a TTA can be determined
Inputs¶
\(v_1(t_\mathit{evasive})\), \(v_2(t_\mathit{evasive})\), \(m_1, m_2\), \(\mathit{TTA}(A_1, A_2)\), \(a_{1,\mathit{min}}(t_\mathit{evasive})\)
Output scale¶
\((-\infty,\infty)\), velocity (m/s), ratio scale
Reliability¶
Comparable to TTA
Validity¶
High validity for severity estimation inside scenario type of TTA, as indicated by empirical analysis against a traffic conflict technique, specifically for actors with different masses [Bagdadi2013]
Sensitivity¶
Medium, as for critical scenarios where no evasive maneuver is identified, CS returns no value
Specificity¶
Comparable to TTA, but increased due to consideration of severity
Prediction model¶
Depends on prediction model of TTA