Q: If China can build a 20-mile-long Donghai Bridge, possibly the longest sea-crossing structure in the world, across an open channel near Shanghai, in four years, for about US$1.2 billion, and the Swiss can bore 35-mile-long twin tunnels, possibly the world's longest overland tunnel, for a high-speed Gotthard Base Tunnel rail link under the Alps between Zurich and Milan, for what they originally estimated at US$6.6 billion, why can't we build a new Highway 520 bridge across Lake Washington for under about $4 billion, or a new tunneled Alaskan Way Viaduct cheaper than the $4.6 billion the state estimated it would cost for a new six-lane tunnel?

It seems others are able to build big, fast, and inexpensively, says Sebastian Cruz of Bellevue.

Compared to the Donghai Bridge, which was completed two years ago, a new Highway 520 floating-pontoon bridge between Seattle and the Eastside would be nearly 15 times shorter. Yet, Cruz laments it could take nearly three times as long to build, and cost about three times more.

"Even when you consider that a new interchange is included in that, it still does not even come close to approaching the scale of the Donghai Bridge," he said. "What accounts for such a staggering difference?"

A: While it's tempting to draw comparisons, some of the biggest differences between projects are in location and structure type, says Kimberly Farley, the state Department of Transportation's Alaskan Way Viaduct and seawall replacement program manager.

The Alaskan Way Viaduct and Highway 520 Bridge are major public works projects that also have to consider timing, and political and economic climate.

Farley says the Donghai Bridge is mostly short spans on piers placed in shallow water, and that's quite different from Highway 520 bridge pontoons floating in Lake Washington's several-hundred-foot-depth.

The Gotthard Base Tunnel is a narrow rail tunnel bored through mountain rock and it's not designed to handle a six-lane road like the tunnel that's been proposed as a replacement for the Alaskan Way Viaduct.

Not surprisingly, says Farley, there are also a number of risks associated with constructing a tunnel in the fill soil on the Seattle waterfront, which increases the cost per lane mile. And both the Highway 520 Bridge and Alaskan Way Viaduct replacements would be in dense urban areas that require extensive mitigation to offset construction disruptions.

Then, too, there's timing. Even the Swiss project is well underway, while rising material costs would significantly increase the final price tags of the Seattle projects, which are still on the drawing board, said Farley. The costs of construction materials have been rising faster than inflation, and that raises the costs of public and private projects across this country. Who knows when the market for construction commodities will stabilize?

"Recently," she said, "there has been greater demand for construction materials from growing economies in Asia, and the industry has been unable to keep up."

Farley said cost estimates for the Alaskan Way Viaduct and Highway 520 projects are in future-year dollars, meaning what they will cost the year construction actually takes place. "This includes predictions by experts about inflation rates and construction material and labor costs," she said.

"We benefit from environmental protections in this country, but they, too, affect cost and schedule," she said. Overseas projects may have less of an emphasis on environmental review and public participation in project development.

And don't forget, labor costs in China are lower. With construction projects, said Farley, labor typically consumes about 70 percent of total project cost.