Question

BOY 1) The Department of Transportation of a Municipality is planning to construct an additional bridge to speed up evacuation in case of an emergency. Two solutions are considered, both with a 50 years life span: Suspension Bridge 600 120 2.5 Cantilever Bridge 550 100 Construction Cost Land Acquisition Annual O&M Annual O&M increase Major Maintenance (at 25 yrs) Decommissioning cost 0.4 0.3 210 190 25 30 (NOTE: all costs are in Million $) The Department uses an interest rate of 8%. Which solution should the Department choose?

Answer 1

NPW of suspension bridge = -600m - 120m - 2.5m *(P/A, 8%,50) - 0.4m *(P/G, 8%,50) - 190m *(P/F, 8%,25) - 25m *(P/F, 8%,50)

= -600m - 120m - 2.5m *12.233485 - 0.4m * 139.592790 - 190m * 0.146018 - 25m * 0.021321

= -834.70 m

NPW of cantilever bridge = -550m - 100m - 3m *(P/A, 8%,50) - 0.3m *(P/G, 8%,50) - 210m *(P/F, 8%,25) - 30m *(P/F, 8%,50)

= -550m - 100m - 3m *12.233485 - 0.3m * 139.592790 - 210m * 0.146018 - 30m * 0.021321

= -759.88 m

As the Present cost of cantilever system is less, it should be selected