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SAE J2735-Draft-Rev15 [issued: 01-30-07]
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152 -
This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
ANNEX A-2 EMERGENCY ELECTRONIC BRAKE LIGHTS
Application Description
When a vehicle brakes hard, the Emergency Electronic Brake light application sends a message to following
vehicles. This application will help the driver of following vehicles by giving an early notification of lead vehicle
braking hard even when the driver’s visibility is limited (e.g. a large truck blocks the driver’s view, heavy fog, rain).
The current brake lamp goes on when the driver applies the brake. The Emergency Electronic Brake Light
application might not only enhance the range of a “hard” braking message but also might provide important
information such as acceleration/deceleration rate. At present, brake lamps do not differentiate level of deceleration
and are only useful as far rearward as line of sight allows.
Flow of Events
Flow of events
1. Vehicle “A” sends MSG_BasicSafetyMessageFrame, Part I
2. Vehicle “B” receives message
3. Vehicle “B” recognizes that Vehicle A’s message is relevant (similar heading in advance of
Vehicle B’s path) and a significant braking event is occurring per the message information (e.g.
deceleration, brake pressure).
4. Vehicle “B” alerts its driver to the braking event and provides some indication of braking
severity.
Hardware Devices:
DSRC radio
Positional Sensors
Human-Machine Interface
Occupant
Vehicle
System
Driver
Passenger
Service
Provider
Road
Department
Actors: (What entities
play an active role in use)
X
X
Support information:
CAMP-VSC Task 3 Report, 2003
Concept of Operation
For this application, it is assumed that the vehicle in an emergency 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 but do not have single hop communication with this vehicle.
The message sender needs to have an algorithm to decide if an “emergency braking” message delivery is
necessary (for example: deceleration greater than 0.6g). If a vehicle determines that it is braking hard then it could
use the On-Board Unit of DSRC to share that information with others. 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.