The replacement of the Alaskan Way Viaduct is not a crisis, but an opportunity. The viaduct replacement can result in a 21st-century transportation solution that not only improves mobility, but enhances Seattle's land use, helps in the battle against climate change and strengthens our local economy.

To realize these ambitious goals, we must let go of our outmoded 20th-century concept that good transportation planning is only about building freeways and moving cars.

A sustainable future for Seattle requires us to look at the full integration of transportation with land use, growth management and environmental policy.

It is crucial now that we make the right choices. It is time to develop a serious, thorough plan for a surface and transit replacement of the aging viaduct that reduces our auto dependency by providing better choices.

Unfortunately, the Washington state Legislature has mandated that Seattle choose between a $2.8 billion rebuild of an elevated freeway (estimated to be about 50 percent larger than the current one) and a $4.6 billion six-lane tunnel. Last month, the Washington state Department of Transportation (WSDOT) released new estimates of the costs for both mega-projects that soared by $1 billion to $1.8 billion for the tunnel and $460 million to $900 million for the rebuild. You can bet the costs will only go up.

When it came time for the Seattle City Council to choose between these two bad alternatives, I reluctantly supported the tunnel option because it is the only choice currently allowed by the state that maintains capacity for 130,000 vehicles while advancing our community's vision for reconnecting the city with the central waterfront.

Limiting our choices to a new elevated freeway or a tunnel ignores the great potential we have to achieve not only a more cost-effective and environmentally sound transportation solution, but remove a blighted condition, spur economic development and add open space to meet our growing city's needs.

Looming over all of our decisions about transportation in the Seattle area is the scary reality of climate change. The scientific evidence is irrefutable — global warming is real. In Seattle, nearly 50 percent of the emissions that contribute to climate change come from burning fossil fuels for our transportation system.

Since both the tunnel and elevated freeway options are now seriously underfunded, state legislators should seize the opportunity to re-examine this problem. There are two key decision makers who can help move this debate forward. Both have shown strong leadership on global warming.

The first is Mayor Greg Nickels, who has launched a national initiative to have cities take over the leadership on climate change from a clueless president. While the mayor's first choice is the tunnel, he supports the City Council's resolution that designates a surface and transit alternative as a backup. Since the tunnel will likely prove to be unaffordable and does not take a single car off of our streets, the mayor should recognize we can do much better than that.

WSDOT's preliminary study showed that 28 percent of the 110,000 vehicle trips that use the viaduct daily could be eliminated by the surface option as people choose alternative destinations, perhaps shopping or doing business closer to home. And that's only a start. Add high-capacity mass-transit service to the corridor and suddenly you give Seattleites a real choice: They can be stuck in heavily congested traffic on a viaduct or in a tunnel, or they can move quickly on a fast, frequent and reliable mass-transit system that is far less polluting.

The second decision maker is Gov. Christine Gregoire. The governor has shown outstanding leadership on climate change. She helped pass the state's clean-car legislation in 2005 and earlier this year she successfully championed a biofuels package that will reduce vehicle emissions.

"We are a coastal state fighting desperately against global warming," she said last year. Surely as she looks at the bad choices the state Legislature put before her to replace the viaduct, she has to realize there is a better choice and a wiser investment. And the final decision rests with her.

There are many questions that remain about a surface and transit alternative. What is the best form of high-capacity transit in the viaduct corridor? Which agencies can we partner with? How much would such a plan cost? How many people could it move? How would it be funded? And how can we ensure commercial traffic gets through fast and efficiently?

We don't know the answers yet because leaders won't commit to seriously studying a 21st-century transportation solution. Old ways are hard to change! We can't afford to miss this opportunity, so let's get started now.

Peter Steinbrueck is a member of the Seattle City Council and chairs its Urban Development and Planning Committee.