Site-Based Video System Design and Development (2012) / Chapter Skim
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Pages 25-35
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From page 25... ...
25 C h a p t e r 5 As described in Chapter 2, the core use of the Site Observer is for addressing SHRP 2 Safety research questions via the use of crash surrogates (conflict measures that correlate with actual crashes) to provide a powerful tool to evaluate crash risk, factor dependencies, and the efficacy of any particular interventions.
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26 Table 5.1. Summary of Kinematic Conflict Metrics Surrogate Conflict Measure Description Gap time (Gettman and Head 2003)
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27 The implication is that, for LTAP/OD cases, the driver is waiting to make a turn and is under pressure to clear the intersection and might misinterpret the oncoming driver decision to stop at the red light. From this perspective, the research team attempted to organize the potential crash surrogates relative to the conflict type and proposed causal factors in Table 5.2, where the causal factor could be observed via a set of surrogate measures departing from baseline driving.
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28 LTIP A vehicle turning left at an intersection collides with a vehicle in the flow in which it is inserting. Run signal Did not see light status • Signal encroachment time • Signal transition deceleration time • Lateral encroachment time Vision obscured • Distance to intersection • Signal transition deceleration time Distraction • Distance to intersection • Signal transition deceleration time Tried to beat amber light • Signal transition acceleration time • Signal encroachment time Deliberately ran red light • Signal transition acceleration time • Signal encroachment time RTIP A vehicle turning right at an intersection collides with a vehicle in the flow in which it is inserting.
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29 accuracy requirements from Conflict Metric analysis Because the estimation of distributions of conflict metrics is a critical application for the system, these provide a significant test case for accuracy requirements: when errors occur in positions and velocities recorded in the trajectory record, these will induce errors in the relevant conflict metrics. To investigate this, one must have an unperturbed exact set of trajectories, which are here provided by simulation, together with an error model.
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30 0 2 4 6 8 10 12 14 16 18 20 0 10 20 30 time (s)
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31 POV subject vehicle Figure 5.5. Vehicle's paths.
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32 0 5 10 15 0 1 2 3 4 5 6 7 8 9 10 ti me (s )
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33 0 5 10 15 20 Meters M et er s 25 30 35 40 -20 -15 -10 -5 0 5 10 Figure 5.8. Effect of medium level spatial errors on the trajectory (blue: reference; black: perturbed)
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34 -4 -2 0 0 5 10 15 20 25 minimum gap -2 0 2 0 2 4 6 8 10 12 14 16 18 maximum gap -1 0 1 0 5 10 15 20 25 PET Figure 5.10. Frequency distribution of summary metrics (LTAP/OD: 100 simulations, medium-level error)
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35 0 0.5 1 1.5 0 5 10 15 20 25 minimum TTC 4 4.5 5 5.5 0 2 4 6 8 10 12 14 16 maximum AR Figure 5.12. Frequency distribution of summary metrics (LTIP: 100 simulations, medium-level error)
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