A contractor’s value-engineering suggestion shaved $2 million off Idaho’s first single-point urban interchange (SPUI), now nearing completion over Interstate 84 near the Boise airport.

Photo: Idaho DOT

Single-point urban design and value engineering saved money

Designer Stanley Consultants, Meridian, Idaho, recommended a SPUI instead of a diamond interchange because it requires less land, moves traffic more quickly and permits wider sidewalks and new bike lanes, says Bob Jacobs, Stanley’s chief transportation engineer. The smaller footprint saved $600,000 by eliminating the need to acquire two buildings.

The $17.8-million cost is funded by the federal stimulus bill. Stanley faced a tight timetable for design. “We had to complete the design in just nine months, and that included two one-month review periods,” says Jacobs. “This kind of project would normally take 18 to 24 months to design.”

A new, 180-ft-long, 192-ft-wide bridge will carry traffic over I-84. Original plans called for a new bridge to be built, then rolled into the place of the old bridge with self-propelled modular transporters. General contractor Central Paving Inc., Boise, suggested building about half the new bridge next to the old, rerouting traffic onto it, then demolishing the old bridge and building the rest of the new one.

“We found we could keep traffic flowing, complete the project just as quickly and save $2 million by building the new bridge in place,” says Central Paving’s project manager Ryan Ward.

The new bridge’s longer, clear spans provide room for the expansion of I-84 below. The daily 54,000 vehicles are expected to increase to 123,700 by 2030.