A semitruck heads north on the Interstate 5 viaduct above Jackson Street in Medford Thursday. Mail Tribune / Jamie Lusch

Could the I-5 viaduct be replaced?

More than $1 billion would be needed to replace the earthquake-challenged Interstate 5 viaduct with a ground-level freeway.

According to preliminary findings in an ongoing $4 million study by the Oregon Transportation Commission, the most popular and expensive idea is to go underground and get rid of the span that crosses Bear Creek and divides east and west Medford.

“Tunneling of the viaduct was surprisingly popular,” said Stacy Thomas, senior project manager with JLA Public Involvement in Portland. “It’s a very big price tag.”

JLA, Kittleson & Associates and other transportation officials are exploring ideas for the future of the viaduct, but they haven’t crunched the numbers for a tunnel, which would have to be 50 to 75 feet underground. Tunneling costs could go much higher than a ground-level freeway, depending on the type of soil found underground.

Also, the distance required to make the tunnel could extend farther than the distance between the north and south Medford interchanges, according to Marc Butorac, senior principal with Kittleson.

The preliminary study, which was presented to the Medford City Council Thursday, has found that any option to improve the viaduct, built in 1962, is expensive, Butorac said.

Transportation officials have placed a high priority on replacing or reinforcing the viaduct and other spans throughout Oregon that would cripple commerce and leave areas isolated in the event of a massive earthquake.

The most expensive option would be a possible 13-mile, ground-level realignment at a rough estimate of $1.1 billion. This route assumes it would traverse eastern Medford, starting at the Fern Valley interchange and ending at Blackwell Road in Central Point.

Tearing down and rebuilding the existing viaduct would cost an estimated $410 million, while a six-lane version of a new viaduct would be $500 million.

The cheapest option would be to retrofit the existing viaduct to keep it standing in a major quake at a cost of from $40 million to $80 million.

The two biggest concerns about the existing viaduct is that it would fail in a major quake, and that it isn't wide enough in case of an emergency.

Based on the study, the viaduct actually performs better than other stretches of the freeway and has fewer slowdowns, Butorac said.

“Generally, the viaduct performs at or above adjacent sections (of the freeway) in the valley,” Butorac said.

Ice on the span, which some longtime residents cited as a problem, is no longer an issue since ODOT began a de-icing program several decades ago.

About 20 percent of traffic on the span is local residents getting on or off at the north and south interchanges. Another 20 percent is residents in Jackson County getting on and off. One possible solution suggested is to create more north-south streets in Medford.

Butorac said some traffic patterns were tracked by using special devices that pick up cellphone data, though he said no personal information was gleaned. The devices were able to track the speed of vehicles on the freeway.

Based on the findings, traffic volume on the freeway is far less than necessary to justify building a new viaduct.

Currently, the viaduct has just over 50 percent of the volume it could sustain. By 2040, it should be about 70 percent. ODOT typically looks at up-sizing a freeway when traffic volumes get to 85 percent, Butorac said.

Over the last five years, the viaduct has had eight reported accidents, Butorac said. The Medford interchanges have had 53 crashes.

“There have been less crashes on the viaduct than other areas of I-5,” he said.

The viaduct was upgraded about 10 years ago to prevent it from “pancaking,” a situation where the travel lanes fall to the ground in an earthquake. Retrofitting the span with greater improvements would prevent it from tipping over or crumbling in an earthquake.

Councilor Clay Bearnson asked where the idea of a tunnel fell in cost estimates.

Butorac responded that it is more difficult to come up with tunnel estimates, citing cost overruns on other tunnel projects.

“It’s much more unreliable,” he said. “It is a big number, and we’ll see if it’s even feasible.”

The commission study indicated it likely would be 2019 before a decision would be made on the viaduct and funding sought for construction.

Reach reporter Damian Mann at 541-776-4476 or Follow on Twitter at @reporterdm.

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