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SAE J2735-Draft-Rev29 [issued: 12-11-08]
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This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
8. Developer Notes
Vehicle Class Compatibility
Cooperative Cruise Control systems utilizing this message set aim to increase mobility, safety, and fuel –
efficiency through enabling low-latency communications between vehicles. Such communications provide
information which allow shorter distances or separation between two vehicles traveling in the same
direction, in the same lane, and at the same speed. A team shall be made up of similar or compatible
vehicle types in order to achieve the same operational characteristics and safety between team vehicles.
Different vehicle platforms have significantly different operational characteristics and therefore make the
benefits to safety and mobility unachievable. For instance, a passenger vehicle and a freight truck have
different acceleration, braking, turning, and reaction characteristics. It would be extremely unlikely if not
feasible at all to implement a system where the two could co-exist in the system environment envisioned
for Cooperative Cruise Control.
Leader to Team Communications
The purpose of the Cooperative Cruise Control message set is to provide a mechanism to improve the
mobility throughput, fuel efficiency and vehicular safety of the roadway through the use of a team or
collective of vehicles. Industry expert experience involved with committee brought to bear during the
development of this message set deem communications between the team leader and team members must
be direct. Direct communications is defined as receiving the message packets directly from the sender of
the packets themselves and not being relayed those packets through an intermediary or other mechanism.
The side effect of in-direct communications proves to undermine the intent of the message set. Even
through the use of low-latent communications, a lag or latency exists between the time a team leader sends
a message and when a team member receives the message directly. Should an intermediary have to receive
the message and relay to following team members the benefit of the information contained in the message
is reduced or lost. In some cases, the effect may be increased. Thus, instead of improving vehicular
reaction time in response to external variables, vehicle reaction times may decrease. The result may
increase the traffic caterpillar or slinky effect. This is also known as adversely affecting the string stability
of the vehicle team.
Reducing the caterpillar effect is the overarching goal of the message set. This is achieved or accomplished
by maintaining team size limits, vehicle class compatibility within teams, and direct communications with
the team leader. These factors may change given the type of low latent communications utilized.
Alterations are left to the implementation of the system.
Broadcast Strategy
The cooperative Cruise Control message set as defined in this document follows a broadcast or non-
acknowledgment response strategy. A broadcast strategy is one in which the communications
infrastructure necessitates a handshaking mechanism which includes dedicated or verified connection.
There is no intent to provide a sense of ad-hoc mobile network functionality through the use of this
message set. That said, vehicle networks based on ad-hoc networking or some other strategy may still use
this message set without needing to modify the message set structure.
Teaming Speed Limit
The teaming concept provides a strategy for vehicles traveling with similar goals, such as speed, heading,
and roadway lane. The strategy is intended to improve mobility, roadway throughput, reduce roadway