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SAE J2735-Draft-Rev28 [issued: 11-10-08]
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This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
operator. The warning can advise the driver to be prepared to take actions to stay out of the path of the
responding vehicle. The warning could include information about:
The type of emergency vehicle
The location or proximity of the emergency vehicle
Instructions on action that the driver may want to take
The warning presented to the driver may be different depending upon the proximity of the emergency
vehicle to their vehicle. The closer the emergency vehicle is, the more severe the warning. If pre
determined emergency route information is available from a public safety vehicle, the information may be
sent via other applications.
In general, private vehicles are expected to ignore signal request and signal status messages. When a
preemption or priority event does occur in an intersection, they are informed of this by way of the
SPAT[RS32] message.
Other emergency vehicles that are responding, receiving the Emergency Vehicle Approaching message,
may use the data to analyze if they may encounter the responding vehicle. The warning can advise the
driver to be prepared to take actions to stay out of the path of the responding vehicle. The warning includes
information about:
The type of emergency vehicle
The location or proximity of the emergency vehicle
Instructions on action that the driver may want to take
The warning presented to the drivers may vary depending upon the proximity of other emergency vehicle
to their vehicle and the use of sirens by one or more responding vehicles. The closer the emergency vehicle
is, the more severe the warning that will be communicated to the operator.
In general, other emergency vehicles may also be sending signal requests and receiving signal status
messages at the same time (often in ad hoc convoys proceeding through the same intersection). The signal
state message may list their own signal requests as pending when another vehicle (ideally one ahead of
them) has been granted the preemption or priority first. When a preemption or priority event is occurring in
an intersection, they are also informed of this by way of the SPAT message, like private vehicles.
5. Application use with DSRC
The two messages transmitted by vehicles in this application are transmitted using the Wave Short Message
protocol (WSM) stack in a periodic broadcast mode on a high power channel to other devices (typically
other mobile OBUs) who have determined to receive this type of message (based on ACID (what is the
correct term for “ACID” now?) value and running a suitable application). Upon reception of such
messages they are examined for message content and relevance regardless of the ACM of the sender. The
message transmitted by the RSU in this application, is sent over the WSM stack with a normal power level.
Therefore, this is a provider application that does not employ a Wave Basic Service Set (WBSS) as per
IEEE 1609.4 Clause 5.3 and there is no confirm and join operations. Receivers of these messages are
expected to process all such message regardless of the ACM found (typically each vehicle running a
provider application will have its own ACM for its transmissions).
This application shall transmit its messages using an ACID value of “19” [the “emergency-warning”
service] as defined by IEEE 1609.4 or its successors. The Application Context Mark (ACM) shall be a 2
byte unique value for each instance of the application. Multiple applications, each with their own ACM,
are expected to be found operating in overlapping local coverage areas. Based on the data exchanged in
this application, devices may determine the need to initiate other services or applications using other ACID
values. The message priority of this application shall be set, as per Annex A of this document, to the value
determined for devices found on vehicles defined as emergency responders who are actively engaged in a