A network design approach to the selection and programming of strategic route improvements to the u.S. National highway network of interstates, four-lane urban highways, and rural principal arterialsis described. Alternative route improvement strategies are defined as mutually exclusive sets of link improvements that can be programmed for construction within any decade of a multidecade planning horizon. Two improvement strategies considered for each route are (a) tomake every link median divided with controlled access and at least four lanes, or (b) to make every link at least four lanes, but without any changes to median division or access control. Route improvement strategies programmed for each decade are constrained by 10-yearfunding allocations. A trip distribution model is used to distribute commodity shipments forecasted for each decade among regions. The example evaluates 536 potential improvements to 289 major highway routes between adjacent bureau of economic analysis regions, or nearlytwo improvement strategies per route. Route improvement benefits are computed as changes in the value of the objective function, which is the total discounted interregional shipment cost for all years ofthe planning horizon. Because different routes and interregional shipments can share common links, a rank-add-and-swap heuristic solution procedure was developed and applied that accounts for the interdependent costs and benefits of route improvements. Implications of this network design approach for strategic planning of the national highway network are discussed. This paper appears in transportation research record no. 1305, Finance, planning, programming, economic analysis, and land development 1991.
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