Field ElementsA number of different technologies can be utilized in the field to monitor traffic conditions， control traffic access and lane utilization， manage incidents， and communicate with Within certain elements， a variety of hardware technologies can be For example， vehicle detection within the surveillance function can be accomplished through inductive loop detection， microwave or radar sensors， video imaging， automatic vehicle identification or location， or other technologies， depending on the type of data Similar alternatives exist for information dissemination， lane use control， and incident management Communications Element Communications can be thought of as the backbone of freeway The communications element transfers information from the field elements back to the traffic control In some cases， instructions and other data are transferred out from the center to the field Reliability and performance are critical issued related to communications system The communications element consists of a number of hardware components and supporting Again， a number of hardware technologies are available upon which to base The two basic categories that exist are buried or aerial cable (fiberoptic， coaxial， twisted pair) or airwave transmission (microwave， radio (including narrow band or spread spectrum)， cellular telephone， and citizen-band radio)Communications infrastructures (and continuing system operational and maintenance costs) are typically the most expensive part of a freeway management FMS functional design must include the communications system concurrently with field devices and central control elements to ensure compatibility and economies of system Control Center Elements The traffic control center is the hub or nerve center of a freeway management It is where information about the freeway system is collected processed， and It can also be the location where decisions about control strategies are made， coordinated with other agencies， and Information dissemination is also typically coordinated and implemented from the The major elements of the control center are the display and control interfaces that link the center to the various field elements through the communications The other major elements of a center are the human operators who monitor conditions and make the adjustments in control and management strategies needed to maximize the efficiency of the freeway Ultimately， the degree to which a traffic control center meets the objectives of the freeway management system depends on how well the human operators are able to interface with the system Relation to National ITS ArchitectureGrowing out of the National ITS Architecture development is the concept of Intelligent Transportation System The term “Infrastructure” has been in common use for a number of years to describe the supporting roadways， bridges， water and sewer lines， and other public works structural items that allow the truck or car; it is the roadway and It is not the water; it is the pipes or conduits that carry the A logical extension of the infrastructure terminology is its application to flow and delivery of information in Intelligent Transportation SMany of the functions needed for ITS implementation are already being provided or supported by a broad variety of ITS infrastructure features， which can serve as the building blocks of a full ITS ITS infrastructure refers to those portions of ITS-related hardware， software， that today and increasingly in the future will manage and support the transportation-related This is typically happening first in the metropolitan areas， but is expanding to include commercial vehicle and rural Freeway management， along with traffic signal control， forms the hub of an integrated transportation The traffic signal control and freeway management components exchange data with each other， allowing the traffic management strategies on the freeways， the freeway entrance ramps， and the surface street network to act as an integrated These data define the actions to be taken by the system when a particular signal timing plan is in effect on the road network， and when a particular sign plan is in effect on the For example， ramp meter timings and traffic signal controls can be coordinated to ensure that queues do not back into When traffic is diverted off the freeway to bypass an incident， the traffic signals timings can be adjusted to handle the increased flow on the At the same time， dynamic message signs can be updated along the arterials to give directions on how to return to the freeway beyond the incident In addition， both the freeway management and traffic signal control components can provide critical information to other components of the transportation Both the freeway management and traffic signal control components are responsible for the surveillances， monitoring， device control and management of the road These components provide information on the status of the roadway system， including link travel times， traffic volumes and speeds currently flowing on the road and These data can be passed to the other components in the overall transportation system， such as incident management and transit management components， and information from these other systems can be channeled through the freeway management and traffic control Although it may be possible for some transportation management subsystems to affect and be affected by the other transportation subsystems to operate in an isolated or independent manner， their operation and functions will affect and be affected by the other transportation This will be particularly evident in an urban For optimal efficiency， the various transportation subsystems must operate in a cohesive， integrated Multiple agencies must maintain open communication and cooperation to achieve the goal of a truly integrated transportation HIGHWAY O2008
