Choosing an option for the Viaduct that permanently removes freeway capacity will increase congestion on I-5. This will likely have a negative influence on the economy, endanger public safety and further restrict freedom of movement. Similar to the highly successful I-405 Corridor Plan, public officials should partner with local jurisdictions and develop a north/south corridor study through Seattle to evaluate these impacts and identify solutions.

Lost Capacity

If the Viaduct is torn down and its traffic-carrying capacity is not replaced, I-5 would become the only north/south freeway corridor through, in, or out of Seattle. Having only one freeway presents a number of regional mobility, safety and economic issues.

The Washington State Department of Transportation agrees that "the viaduct plays a major role in sustaining our economy and maintaining our citizens' ability to move to and throughout Seattle. One quarter of all north-south traffic through Seattle (110,000 vehicles) use the viaduct every day. Extreme congestion on I-5 and in the downtown city grid following the 2001 Nisqually Earthquake closures made it clear this is a critical route that needs replacing."

Relying on a single north/south freeway through Seattle could create a variety of traffic, safety and economic impacts.

- In the event of an emergency, where mass evacuations are ordered, a single north/south corridor would fail to absorb the high demand.

- Without another north/south corridor or capacity improvements to I-5, freight mobility into or through Seattle would be negatively impacted. These impacts would increase the costs of moving goods-to-market and have a rippling economic affect throughout the state.

- Without another north/south corridor or capacity improvements to I-5, passenger vehicle mobility would be negatively impacted. This increased delay would be on top of the daily congestion travelers already endure.

- Increasing mass transit along the waterfront, without other increases in road capacity will not relieve traffic congestion. Ninety-four percent of daily trips are in private automobiles, a percentage that has not changed in 25 years. Nor will transit prevent the inevitable increases in delay for commercial vehicles or freight traffic.

A Successful Model

Between 1999 and 2002, the (state department of transportation) partnered with more than 35 agencies, local municipalities, and public and private sector experts to complete a corridor plan for I-405. The purpose was to develop a strategy for reducing traffic congestion for both passenger and commercial vehicles. It included a Tier 1 Environmental Impact Statement and a long-term master plan. The study identified a cost of $11 billion and more than 300 projects to improve the Eastside corridor over the next 20-30 years. Construction on several of the projects identified in the plan began in 2004 and it continues to serve as the blueprint for long-term improvements for the Eastside.

In light of the governor's plan to tear down the current Viaduct by 2012, it only makes sense for state officials to perform the same type of analysis on I-5 through Seattle. The corridor plan should provide transportation planners with ideas on how the region will react to Washington's largest city having only one north/south corridor and more importantly, how that will affect passenger vehicle mobility, freight mobility and public safety. The I-405 Corridor Plan was a successful model and leaders should implement a similar strategy on I-5 through Seattle.

Conclusion

The governor's plan to spend $915 million on the Viaduct appears to be the first step in replacing the current structure with some form of surface option. Reducing the supply of freeway capacity will result in negative impacts not only in Seattle, but regionally. Relying only on I-5 to support all of the north/south mobility demands through Seattle will jeopardize public safety, create negative economic fallout and increase traffic congestion. Transportation leaders must consider these implications and fund a corridor study to define these new demands and how to best address them.

Michael Ennis is the Director of the Center for Transportation Policy. Before Joining Washington Policy Center , Michael worked for the Washington state Senate and House of Representatives and was formerly a staff assistant for U.S. Senator Slade Gorton. Michael served in the U.S. Army with the 2nd Ranger Battalion and has been active in local government affairs. He earned his Bachelor's degree from the University of Washington where he studied Political Science. He also earned his Master's of Public Administration degree from the Daniel J Evans School of Public Affairs also at the University of Washington.