Light rail is the core of Sound Transit 3, the regional transportation plan on the ballot in three Puget Sound counties.
The 62 miles of new rail make up the largest part of the $54 billion price tag, but the region wouldn't see most of it until after 2025.
One way of looking at why Sound Transit is so focused on light rail is to look at Everett and Snohomish County.
Right now, it takes anywhere from 40 minutes to more than an hour to get from downtown Seattle to Everett by bus. If ST3 passes, Everett would get light rail by 2036. Sound Transit estimates the trip would take about 60 minutes.
Of course, Everett isn't the only city getting light rail. If ST3 passes, rail would also go down to Tacoma, east to Redmond and Issaquah, and west to Ballard and West Seattle.
But what makes Snohomish County interesting is that it's the least populous of the three voting on ST3.
Is light rail worth the cost?
ST3 critics have said that light rail tends to work best in densely populated areas, from a cost-benefit perspective. Light rail is expensive to build. Rebuilding transit infrastructure from the ground up is hard, especially in this region.
Part of Sound Transit's thinking is that light rail is more efficient; they can move more people by train than they can by bus or by car. It's the consistency and efficiency that makes light rail worth the expense.
The counter-argument admits that it's possible that a place as dense as Seattle could reach a critical mass of riders to justify the cost, but critics worry that some other areas can't. Knowing that ST3 would raise three taxes, that's something for voters to consider.
A regional system
But that brings us back to Snohomish County.
Back in March, when Sound Transit unveiled the first iteration of this plan, the Lynwood-to-Everett leg wasn't scheduled to open until 2041.
Leaders in Snohomish County came out against the plan because they thought that was too long for light rail to Everett. They wanted rail sooner.
Their argument, and the other part of Sound Transit's justification, is that these areas shouldn't be thought of in isolation.
Snohomish leaders argued that Everett has a lot to offer the region and they wanted to be connected to any transit system that will move people efficiently through that whole region.
This is Part II of our series Sound Transit 3: The $54 Billion Question.