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Track: Transportation, Logistics Planning
Dale Hamilton
University of Montana
Social Science Building Room 401
Missoula, MT 59812-1008
Telephone: 406-273-2815
Fax: (406) 273-5425
E-mail: hamilton@cs.umt.edu
Ray Ford
Analysis of Road Network Accessibility
Many interesting problems in natural resource management involve the assessment of the impact of vehicle traffic moving into, through, and out of a designated area via a road network. In order to exactly determine the extent of the influence of the road network, it is necessary to determine which segments of the network are accessible to vehicle traffic, when they are accessible, and to what classes of vehicles they are accessible. These determinations can be made using a derivative of a classical "connected components" graph algorithm, taking as inputs the road network represented as a graph and an associated set of "barriers" that constrain travel across the network. In practice, barriers are real constraints such as gates, kelly humps, revegetation, and so forth. Algorithmically, barriers are represented as nodes on the graph, attributed with values that define the nature of the constraint. The algorithm groups together "connected arcs" as those that are accessible to each other without passing
through any barriers. The algorithm next determines the effects of the restrictions imposed by the barriers on each set of connected arcs. Algorithm output is the road network represented as a graph with arcs attributed according to the nature of the travel restriction imposed by the set of barriers. The presentation will focus on the algorithm and explain how it complements the analysis available using only the facilities embedded in a typical commercial GIS such as Esri's ArcInfo. Examples will be provided to show how the algorithm can be used to record the arc restriction attributes for use with other types of analyses. The examples will also show how the algorithm can be utilized to display which portions of the road network are restricted for a given set of dates. Additional types of analyses that will utilize arc restriction attributes as input data will be discussed. These include various metrics such as road density by date, total accessible road distance by date, nonaccessible or roadless
area identification, and the moving window analysis from the grizzly bear recovery program.
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