Space Occupancy Index (SOI)¶
Description¶
The SOI defines a personal space for each actor and counts violations by other participants while setting them in relation to the analyzed period of time [Tsukaguchi1987] [Ogawa2007] [Johnsson2018]. For each actor \(A_i\) at time \(t\), a personal space \(\mathit{Sp}(A_i, t)\) is defined. At time \(t\), if there exists some \(A_j \neq A_i\) s.t. \(\mathit{Sp}(A_i, t) \cap \mathit{Sp}(A_j, t) \neq \emptyset\), a violation of the personal space of \(A_i\) is given. The number of conflicts is then given as \(C(A_1, \mathcal{A}, t) = \sum_{A_j \in \mathcal{A}\setminus\{A_1\}} [\mathit{Sp}(A_1) \cap \mathit{Sp}(A_j) \neq \emptyset]\), where \([\cdot]\) denotes the Iverson bracket. Thus, for a given scenario in the time interval \([t_0, t_e]\), the conflict index is defined as
SOI was introduced for bicycles and pedestrians, however, it is possible to formulate a similar concept for road vehicles.
Properties¶
Run-time capability¶
Yes, but only retrospectively
Target values¶
No
Subject type¶
Originally defined for VRUs, could be extended to road vehicles
Scenario type¶
Any scenario
Inputs¶
Actor type, size of safe space depending on type
Output scale¶
\([0,\infty)\), hertz (1/s), ratio scale
Reliability¶
Medium, due to the nominal nature of the conflict definition, which leads to fluctuations if vehicles exist close the boundaries of personal space
Validity¶
Medium, since temporal and dynamical aspects are ignored due to binary evaluation; no empirical analysis available
Sensitivity¶
Medium, as already a single safe space violation can lead to an accident
Specificity¶
Medium, as multiple safe space violations are associated but with but not necessarily causative for accidents
Prediction model¶
None, since a-posteriori