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SAE J2735-Draft-Rev29 [issued: 12-11-08]
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242 -
This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
Concept of Operation
For this application, it is assumed that the vehicle in a hard braking situation would be equipped with a
DSRC unit. It is also assumed that the message from the vehicle would be received by the following
vehicles, including any that could have a collision with the braking vehicle.
The message sender needs to have an algorithm to decide if a hard brake was performed (for example:
deceleration greater than 0.4g), and if a non-routine event message transmission is advisable. If a vehicle
determines that it is braking hard then it could inform the surrounding vehicles by sending a
MSG_BasicSafetyMessage, possibly including an optional “hard-brake” event flag. The message could be
sent at the next scheduled transmission time, or earlier, and it could use a higher priority level than the
routine broadcast of a MSG_BasicSafetyMessage.
In order to determine if a hard braking message is relevant, the listening vehicle needs to know the relative
location from which the message originated (e.g., front, rear, left, right). This can be done based on its GPS
information and the GPS information of the braking vehicle. The listening vehicle may not necessarily
inform the driver of such an event if the braking vehicle is traveling in an adjacent lane.
Sensors and Other System Needs
A map database, where available, may help to provide specific, relevant information related to current road
segments. This could allow, for example, intersection geometry or road curvature to be taken into account
when an application host vehicle evaluates the received MSG_BasicSafetyMessage to see if an alert to the
driver is necessary.
Annex C-3 Pre-crash Sensing
Application Description
Pre-crash sensing can be used to prepare for imminent, unavoidable collisions. This application could use
DSRC communication in combination with other sensors to mitigate the severity of a crash.
Countermeasures may include pre-tightening of seatbelts, airbag pre-arming, front bumper extension, etc.
Flow of Events
Flow of events
1.
Vehicle “A” sends MSG_BasicSafetyMessage
2.
Vehicle “B” receives message
3.
Vehicle “B” processes the message from Vehicle A and determines that Vehicle A’s
message is relevant and, per the message information (e.g. location, speed, heading,
deceleration, brake pressure, etc.), that trajectories of Vehicles “A” and “B” will likely intersect
imminently.
4.
Vehicle “B” automatically initiates pre-crash countermeasure(s).
Hardware Devices:
DSRC radio
Positional and vehicle sensors
Human-Machine Interface
Actors: (What entities play an
active role in use)
Vehicle
Occupant
Service
Road
Department