193. Introduction to Safety Metrics

Safety metrics are part of the Evaluation V-Suite Library. They are available as methods on physical_object and vehicle actors and provide quantitative measurements of the safety properties of a driving scenario at runtime. Safety metrics can be used within evaluation scenarios, KPIs, and custom checkers to assess the behavior of the actors under evaluation.

Safety Metrics are organized into two categories:

Proximity Metrics measure the temporal and spatial closeness between road users. These include time-based measurements such as Time To Collision, Modified Time To Collision, Time Headway, Time Gap, and Deceleration Rate to Avoid a Crash (DRAC). These metrics quantify how close two actors are to each other and are commonly used in KPIs and coverage items.
Crash Severity Metrics quantify the severity of a collision event. These include Delta-V, the Principal Direction of Force (PDOF), and the crash severity classification. These metrics are used to evaluate the impact of a collision and are relevant for post-collision analysis and safety assessment.

193.1 Proximity Metrics

Name	Return type	Actors	Method	Description
Time To Collision (TTC)	`time`	Physical objects	`physical_object.get_ttc_to_object()`	Returns the time until a collision between two objects, assuming constant velocity. Returns `inf` if no collision is predicted within `ttc_calculation_limit`. For details, see get_ttc_to_object().
Modified Time To Collision (mTTC)	`time`	Physical objects	`physical_object.get_mttc_to_object()`	Returns the time until a collision between two objects, projected using constant global speed and acceleration. Returns `inf` if no collision is predicted within `ttc_calculation_limit`. For details, see get_mttc_to_object().
Minimum TTC	`time`	Physical objects	`physical_object.get_min_ttc_to_objects()`	Returns the minimum TTC between the current object and any object in a provided list. For details, see get_min_ttc_to_objects().
Minimum mTTC	`time`	Physical objects	`physical_object.get_min_mttc_to_objects()`	Returns the minimum mTTC between the current object and any object in a provided list. For details, see get_min_mttc_to_objects().
TTC Info	`collision_data`	Physical objects	`physical_object.get_ttc_info_to_object()`	Returns collision prediction data (including predicted collision position, side, and speeds) based on TTC projection. Returns `null` if no collision is predicted. For details, see get_ttc_info_to_object().
mTTC Info	`collision_data`	Physical objects	`physical_object.get_mttc_info_to_object()`	Returns collision prediction data based on mTTC projection. Returns `null` if no collision is predicted. For details, see get_mttc_info_to_object().
Time Headway (THW)	`time`	Physical objects	`physical_object.get_time_headway()`	Returns the time headway from the current object to another object, measured front-to-front along the planned path. For details, see get_time_headway().
Time Gap (TG)	`time`	Physical objects	`physical_object.get_time_gap()`	Returns the time gap from the current object to another object, measured front-to-back along the planned path. For details, see get_time_gap().
Deceleration Rate to Avoid a Crash (DRAC)	`acceleration`	Vehicles	`vehicle.get_drac()`	Returns the minimum deceleration required by the vehicle to avoid a collision with an object ahead in the same lane. Returns `math.max_acceleration()` when the object is out of range, or zero when the vehicle is not approaching. For details, see get_drac().

193.2 Crash Severity Metrics

Name	Return type	Actors	Method	Description
Delta-V and PDOF	`collision_dynamics_data`	Vehicles	`physical_object.get_delta_v_and_pdof()`	Returns the Delta-V magnitude and Principal Direction of Force (PDOF) angle for both objects involved in a collision, using a 2D inelastic collision model. For details, see get_delta_v_and_pdof().
Crash Severity	`crash_severity_data`	Physical objects	`physical_object.get_crash_severity_data()`	Returns a structured classification of the collision severity (`S0`–`S3`) for both objects involved, based on Delta-V for vehicle-to-vehicle collisions or vehicle speed for vehicle-to-VRU collisions. For details, see get_crash_severity_data().