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SAE J2735-Draft-Rev28 [issued: 11-10-08]
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260 -
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 an hard braking situation would be equipped with a
DSRC unit. It is also assumed that the message from the vehicle would be sent to 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 0.3g for longer than 2 seconds) , and if an event message delivery is necessary. If
a vehicle determines that it is braking hard then it could. inform the surrounding vehicle through DSRC
communication. The sending vehicle could use the MSG_BasicSafetyMessageFrame, Part I and
MSG_BasicSafetyMessageFrame, Part II messages to issue this warning through the use of a higher
priority level than the routine broadcast of MSG_BasicSafetyMessageFrame, Part I and
MSG_BasicSafetyMessageFrame, Part II. The sending vehicle could also include an event flag to indicate
the type of the emergency event- Emergency Brake Event.
In order to determine if a hard braking message is relevant to the listening vehicle, 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
vehicles may not necessarily inform the driver of such 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 “emergency braking message” to see if an alert to the driver is
necessary.