PORTLAND - A cold snap brought a blanket of snow, rain, sleet and freezing rain to the Portland and Vancouver Metro areas Tuesday morning, literally and figuratively freezing roads and traffic during the morning commute and cancelling classes at many schools.

Roads were so icy that ODOT required all vehicles in the Portland Metro area to use chains or traction devices on highways until further notice.

Jacknifed semi-trucks were scattered along highways, including some blocking traffic on Interstate-205 northbound in Clackamas and Interstate-5 southbound near the Main Street exit in Vancouver.

Police warned that they would only be responding to injuries, so people involved in fender benders or spin-outs would need to call for their own help from tow trucks, due to the large number of accidents Tuesday morning involving everything from cars and semi-trucks to TriMet and school buses.

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Drivers had a slippery time during their morning commute after an arctic blast delivered several inches of snow to the Portland metro region.

In Portland, a firetruck was responding to a six-car pileup and got struck by a sliding car at SW 21st and Salmon. No one was injured but the accident blocked the roadway. One resident heard crunching outside his apartment and witnessed about 15 car accidents at the intersection, many of which he captured on home video.

Snow was falling all across the Portland Metro area, with the heaviest accumulation on the West side. Across the border in Vancouver, Southwest Washington was also getting snow and freezing rain.

Portland International Airport's morning flights were generally on schedule, however, said spokeswoman Kama Simonds.

The National Weather Service issued snow advisories for the western Columbia Gorge, the foothills of the northern Cascade Range and the northern Willamette Valley.

It predicted two to four inches would fall through much of those areas.

It issued a freezing rain advisory for the southwestern corner of the state and warned of winter weather conditions through much of the rest of northern Oregon.

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With streets like ice skating rinks, cars and even one fire truck were sliding around like bumper cars on Portland streets.

In Tualatin, officials said a family taking a woman in labor to the hospital got stranded in the snow along Highway 217, but a rescue squad got her to the hospital in time to deliver.

Another search and rescue team went to a Beaverton home to take a pregnant woman to the hospital, officials said.

After eight crashes in less than an hour during freezing rain, officials closed Highways 126 and 36 in the Mapleton area near Florence.

ODOT Spokesman Joe Harwood in Springfield said Interstate 5 between Springfield and Albany was "pretty treacherous" and one lane of Oregon 99W near Monroe was closed because of ice.

Crossings over the Coast Range were slippery he said, and motorists were advised "to avoid them at all costs. If you don't have to cross over the Coast Range today, please don't." He said he stopped counting accidents in the central part of the mountains at 15.

He said dozens of other accidents in the region were reported.

Harwood said warmer afternoon temperatures were expected to melt much of the snow and ice but that the resulting moisture likely will freeze Tuesday night, making for a dangerous Wednesday morning commute.

In Portland, the snow started falling Tuesday just as the morning commute began. The public transit agency, Tri-Met, said it was chaining the tires of its buses. It curtailed service on 10 routes and canceled three others.

Many schools closed or opened late. Oregon State University announced that it would not open until 11 a.m.

ODOT said conditions over the main Cascade passes generally were limited to packed snow and spots of ice. U.S. 101, the main coastal highway, was reported generally clear.

The Associated Press contributed to this report.