EUGENE, Ore. (AP) A new section of Highway 20 that was designed to replace a deadly 10-mi. (16 km) section between Pioneer Mountain and Eddyville has been dogged by cost overruns and is not scheduled to open until 2015, according to the Oregon Department of Transportation.

The Register-Guard reported construction is six years behind schedule with cost overruns of $170 million and the new section has turned into Oregon’s most expensive state highway project.

The 5.5-mi. (8.8 km) stretch through the crest of the Coast Range was supposed to replace a highway that contained sharp turns and tempted drivers to cross double yellow lines to pass.

The state in 2003 issued a $130 million contract, its largest ever, to replace the dangerous section. The proposed alignment cut straight through slopes as steep as 66 percent and included nine new bridges over fish-bearing streams.

But construction challenges have meant four of the nine bridges in varying stages of construction have had to be demolished.

The department now estimates the project cost at $300 million.

ODOT representatives and the agency’s original contractor, Granite Construction, blame most delays on unstable earth deep beneath the surface that was left by landslides that occurred thousands of years ago.

The company discovered the seriousness of the stability problem when it sank bridge pillars 6 ft. (1.8 m) in diameter 55 ft. (16.7 m) into the earth.

The Register-Guard reported problems of failing to accurately assess the landslide risk were exacerbated by the state’s rush to meet a deadline to acquire federal construction money and by a contractor with no experience in unstable terrain of the Coast Range.

The state and the company are no longer working on the project together under a design-build contract.

The agency has redesigned the remaining portion of the project using its own staff.

Granite officials declined interview requests.