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There’s a critical piece of Western Washington’s infrastructure that is largely being ignored in the debate over the future of transportation, a former outspoken state employee says. And that critical piece is Interstate 5.

Doug MacDonald, the former secretary for the Washington State Department of Transportation, told that whether or not the ST3 tax package that would expand light rail throughout three counties is approved, Interstate 5 will remain a crucial piece to our transportation puzzle.

“I-5 has to work under any theory of the future,” he said. “It is an orphan. It is not in any of these programs and I think that is a very telling critique of where we are.”

The benefits of ST3 would be mostly seen decades in the future. One of the supporting arguments is you have to pay it forward; you have to do this for the next generation. But MacDonald points out that the next generation will also rely upon Interstate 5.

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The current , which was approved in 2008 and is are already being funded by taxpayers, includes regional express bus routes and commuter rail service while adding 36 miles of light rail to the regional system.

But no matter what is built, MacDonald argues that reliance on I-5 isn’t going to go away. Essentially, the freeway carries hundreds of thousands of motorists a day and expanded public transit isn’t likely to drastically change that. The bulk of benefits light rail will bring to the region has already been approved, he says.

There’s another mode of transportation being largely ignored as well: walking. Walking, according to MacDonald, is already a main commute method in Seattle.

“Walking is the fastest growing way people get around … way faster than transit,” he said. “Transit in downtown Seattle already serves 45 percent of the people going to work … if we make the light rail investment, what will that number be in 2040? That number goes from 45 percent to 52 percent.”

Instead of further developing transit, MacDonald says Seattle just needs more urban housing so people can live closer to where they work.