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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.
3.73 reference point: A reference point is a complete latitude – longitude – and vertical point on the
reference surface which is used as an initial starting point for subsequent orthogonal offset X, Y, Z values
from that point. All roadway geometry, maps of intersections, lane and curve descriptions, and other
geometrical data that is encoded in this standard uses a systems of local reference points to index and offset
the data that follows.
3.74 registration: One of three modes, or states, of operation known as Registration, Initialization, and
Operations which DSRC systems operate in. The Registration mode is the process by which critical
parameters pertaining to the device and applications using it are entered into the device's Management
Information Base (MIB). Registration must be completed before a DSRC device can be ready for
operations. The registration process is defined in IEEE P1609.3 and is controlled by the WAVE
Management Entity (WME).
3.75 road side unit: A Road Side Unit (RSU) is a DSRC device used to transmit to, and receive from,
DSRC equipped moving vehicles (OBUs). The RSU transmits from a fixed position on the roadside
(which may in fact be a permanent installation or from "temporary" equipment brought on-site for a period
of time associated with an incident, road construction, or other event). RSUs have the ability to transmit
signals with greater power than OBUs and may have TCIP/IP connectivity to other nodes or the Internet.
3.76 semi-actuated operation: A type of traffic control signal operation in which at least one, but not all,
signal phases function on the basis of actuation.
3.77 service channel: Secondary channels used for application-specific information exchanges.
3.78 service table: A data store containing the pertinent information about applications available through
the WAVE device.
3.79 signal head: An assembly of one or more signal lamps. One or more signal heads maybe used to
provide complementary indications to one of more approaches, which may cover multiple lanes. The
definitive mapping to specific lanes can be determined by examining the SPAT and MAP fragment
messages.
3.80 signal phase: The right-of-way, yellow change, and red clearance intervals in a cycle that are assigned
to an independent traffic movement, or combination of movements. Each of these cycles are reflected in
the SPAT message for the lanes that are part of the movement(s), along with its expected timing interval
(which may be updated in signal systems that vary the time interval based on actuation or other methods).
3.81 signal section: Two or more traffic control signals operating in signal coordination.
3.82 signal system: Two or more traffic control signals operating in signal coordination.
3.83 signal timing: The amount of time allocated for the display of a signal indication, slang.
3.84 SPAT: In the context of this standard, Signal Phase And Timing (SPAT), is a message type which
describes the current state of a signal system and its phases and relates this to the specific lanes (and
therefore to movements and approaches) in the intersection. It is used along with the MAP message to
allow describing an intersection and its current control state.