Updated at 3:44 p.m.

The Oregon Department of Transportation will announce plans Friday to begin using rock salt to melt ice and snow on roads across the state.

The state will continue its use of magnesium chloride solution. But in specific problem areas, such as steep hills, it also will spread down rock salt to speed melting and improve traction. ODOT spokesman Dave Thompson said the use of salt would be "surgical," not widespread.

The agency used rock salt on a nine-mile stretch of Interstate 5 near Salem overnight, which allowed workers to break through ice on the road and lift a tire-chain order. It could also use salt on problem spots in the Portland area, like Sylvan Hill along U.S. 26 and Breeze Hill on I-5 near Tigard.

Salt would only be used when other options have failed, Thompson said.

The state recently began using road salt near its borders with California, Nevada and Idaho -- states whose use of road salt previously made for a treacherous transition at the border with salt-free Oregon.

As part of the pilot project, ODOT built salt-storage and specialized truck-maintenance facilities near the Siskiyou Mountains and in the southeast corner of the state. It doesn't have those facilities near Portland, so the salt will have to be trucked in.

The policy change comes after an afternoon snowstorm brought Portland traffic to a standstill. Hundreds of thousands of commuters hit the roads at once, and some were stuck in congestion for as much as 10 hours.

"We are saying that we've been listening to citizens," Thompson said. "We still ask citizens to remember that there's a shared responsibility to being safe on the road."

He said Oregonians should still plan ahead when snow is in the forecast and avoid unnecessary travel.

The city of Portland also is reexamining its de-icing procedures. Commissioner Steve Novick, who oversees the city's transportation bureau, ordered the review after Wednesday's storm.

But the city won't be making a policy change overnight. Unlike ODOT, it doesn't have a supply of salt or a facility in which to store it. Transportation bureau spokesman John Brady said any change ultimately will be made by the City Council.

The state has long used magnesium chloride as an alternative to rock salt, primarily because rock salt has been tied to increased contamination of groundwater.

Magnesium chloride, however, is not without its own problems. It, too, can break down into ions that can infiltrate groundwater, and it's also dangerous to plant and animal life. It can be as corrosive as salt, so it must be mixed with an anti-rusting agent to prevent damage to vehicles and infrastructure.

An ODOT-sponsored study also found that magnesium chloride had worrying effects on concrete, particularly on the state's bridges. What's more, the damage was only apparent from samples taken from the bridge, not from a visual inspection.

"They look very good on the surface, but when you look inside, they're significantly compromised," said Washington State University professor Xianming Shi, who conducted the research. "That's pretty scary, because that means our traditional inspection method doesn't work in that environment."

Shi, a civil engineering professor who studies road de-icing techniques and their environmental effect, said magnesium chloride is generally more effective than rock salt in similar amounts.

But salt brines with chemical additives can be nearly as effective. And magnesium chloride's main benefit -- that it works in colder weather -- doesn't do much for Portland, where temperatures rarely fall far below freezing.

"When the pavement temperature is warm, you're usually better off with sodium chloride or salt brine," he said.

In any case, Shi said, it's usually best to have several options available.

"A toolbox approach is best," he said. "I don't think one size fits all."

-- Elliot Njus

enjus@oregonian.com

503-294-5034

@enjus