PORTLAND - Under federal orders, state highway engineers planned Friday to spend up to a month inspecting Oregon bridges of the type that collapsed into the Mississippi River.

State engineers identified 28 bridges, including one of the state's busiest: The 1966 Marquam bridge that carries Interstate 5 over the Willamette River in south Portland.

Federal highway officials called Thursday for state agencies to double check steel deck truss bridges like the Interstate 35W bridge in Minneapolis. It failed Wednesday, and at least five people died.

The truss in a truss bridge is a latticework of beams and girders that describe triangles, and it supports the roadway, or deck. The deck can be atop the truss, as are the northbound lanes of the Marquam bridge. Or the truss can rise above the roadway, as in many bridges over small streams in rural America.

Alternative bridge styles include spectacular suspension bridges such as the Golden Gate Bridge or arch bridges such as the Fremont Bridge across the Willamette in north Portland.

The Marquam carries about 130,000 vehicles on an average day, said Dave Thompson, spokesman for the Oregon Department of Transportation, about 10,000 fewer than the Minnesota bridge.

The Marquam and the Glenn Jackson bridge that carries I-205 across the Columbia River are Oregon's two busiest, Thompson said. The Jackson bridge is not of a type subject to the inspections that federal officials ordered.

Gov. Ted Kulongoski asked the state Department of Transportation on Friday for a status report within a week.

Thompson said the state's corps of bridge inspectors want to finish their inspections within two to four weeks.

Nine of the bridges to be checked are on Oregon's interstate system, eight carry U.S. highways and 11 carry state highways.

Most of the interstate bridges are in the Medford area, Thompson said, built during the first flush of Oregon interstate construction in the 1960s.

The state considers eight of the bridges to be inspected to be “functionally obsolete,” often with weight restrictions because they can't carry contemporary volumes and vehicle weights.

Six are listed as structurally deficient, which means that have components that have deteriorated, though they are not necessarily unsafe, the department said.

Thirteen, including the Marquam, have no deficiencies, transportation officials said.

One, on a frontage road in Eastern Oregon, is closed.

Thompson said some of the inspections will include divers checking for underwater dangers, such as those posed when currents scour riverbeds away from bridge piers, or the legs on which a big span stands.

Inspectors from state agencies and private contractors will be pressed into service, Thompson said.

Kulongoski said Oregon “has been ahead of the curve nationally, investing millions of dollars in the maintenance and repair of hundreds of bridges across the state over the last four years.”

In his first term, the Legislature approved a $1.3 billion, 10-year state-funded project to fix 365 state bridges found in most need of repair. More is earmarked to check city and county-owned bridges.

Kulongoski pledged a “comprehensive statewide transportation plan for the 2009 legislative session.”