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The following discusses how the National ITS Architecture provides the transportation service described by this service package. Each numbered item describes the operation of that portion of the service package identified with the corresponding number on the transaction set diagram.
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Intersection safety warnings can be provided by a combination of infrastructure-based and vehicle-based systems. Some implementations rely on the vehicle's ability to determine its precise location on the road network. Map updates ensure that the vehicle has current map data as an intersection is approached. Map data may be requested by the vehicle (map update request) for an entire region or dynamically as it moves through the network, depending on implementation.
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The driver controls the on-board systems that provide safety warnings (driver inputs). The vehicle monitors its current position relative to the intersection (position fix), detects vehicles, pedestrians, and other objects in the vehicle's path (physical presence) and monitors the driver's current control of the vehicle including basic vehicle measures such as vehicle speed, acceleration, anti-lock brake status, traction control status, acceleration, and turning movement.
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The Vehicle monitors its approach to the intersection and detects potential hazards. It uses short range communications to send it's current position, motion, and anticipated path through the intersection to other vehicles approaching the intersection and to field equipment at the intersection (vehicle intersection safety data).
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For implementations that allocate intelligence to the intersection, vehicle intersection safety data is collected from approaching vehicles and sensors are used to monitor approaching traffic that may include unequipped vehicles (traffic characteristics). The intersection uses short range communications to send intersection status to the approaching vehicles that includes signal phase and timing information, intersection geometry, warnings of potential violations and hazardous conditions, and approaching vehicle information.
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The vehicle processes data collected from on-board systems and/or information received from the intersection and provides safety warnings to the driver, notifying the driver of potential hazards or violations (driver updates).
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The intersection may also use signs and signals to warn approaching vehicles of hazardous situations. In this case, the intelligent intersection activates the signal or sign (roadway equipment coordination, which provides the warning to approaching traffic (driver information).
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