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SAE J2735-Draft-Rev29 [issued: 12-11-08]
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277 -
This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
etc). The second is identification of where the vehicle is and what to do to avoid interference with its path.
It should also be noted that many times police will respond to a service call with lights flashing but without
sirens being active (an event which is also covered
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).
When an emergency vehicle and other surrounding vehicles are equipped with PSOBU’s and OBU's, the
vehicles can establish communication when they are within range of each other and share information
relative to their location and direction. A PSOBU is required in emergency vehicles as this is a special
application that is not available to standard OBU's. This application should be implemented as a high
powered application to extend range. It is expected that the surrounding OBUs will receive this message
from the PSOBU well before they begin to receive the normal BSM transmission from the same vehicle.
From calculations resulting from this information, the private vehicle can first notify its driver of the
situation then may offer suggestions to avoid path interference. While difficult to make this function
robust and precise, enough information can be made available to the driver that improvements over a non-
equipped system can be significant.
2. Preconditions for operation:
The following general conditions are presumed to prevail in this application:
1.
The private vehicles are equipped with active OBU.
2.
The emergency vehicles are equipped with active PSOBU
and can issue SRM and EVA messages.
3.
The emergency vehicles has previously received a MAP message for the target intersection which
contains “zone” data [RS42]to relate specific priority or preemption values to specific service zones
in the intersection.
4.
The intersection is equipped with an RSU and ASC[RS43].
5.
The intersection [RS44] equipment can handle the intersection control messages
(SPAT, MAP, SRM, SSM).
6.
All systems are active and functional.[RS45]
7.
Emergency vehicles can provide location, speed, and direction of travel. This is required for the
EVA message and optional for the SRM message. The messages can be used when the direction
of travel is unknown (often the case when a vehicle is pulling out into traffic). ITIS codes and
speed./heading denote when a vehicle is stopped (indicating at scene).
8.
Private vehicles have available thier location, speed, direction of travel.
3. Flow of Events
The first two messages are handled in the initial use case to control the intersection. The 3rd messages is
then handled in another use case. In actual practice, the flow of events of these two use cases would be
interspersed in time.
Flow of events, Typical Intersection use
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Alerting others to the presence of the siren or flashing lights is optional and the standard allows for
“silent running” response as well. Police officials differ in opinion on the utility of this aspect of the
message, so its use is optional.