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East Link light rail, I-90 bridge, Mercer Island
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The budget story behind the East Link light rail over I-90

The I-90 express lanes between Mercer Island and Seattle were permanently closed Monday. (WSDOT)

We all heard last week about the $221 million cost overrun of the East Link light rail project over the I-90 floating bridge. And we all rolled our eyes and shook our collective fists. But it’s not like a massive construction project running wildly over budget is anything new around here.

What is new is that this light rail line will roll over a floating bridge. That’s never been done anywhere in the world before. Which poses some unique and costly design challenges.

Related: Trump budget slashes money for Puget Sound light rail expansion

East Link Executive Director Ron Lewis knows where all those cost overruns are coming from. And he knows of concerns we may not have heard before. He is quick to note that the entire $3.7 billion East Link extension — which branches from the station in the International District, across I-90, through Mercer Island and Bellevue to end up in Redmond — is not over budget yet. So even though the I-90 portion is over budget, there are six other design projects in East Link – those are all on track and either at, or under budget.

East Link light rail costs

Even though I-90 was supposed to be designed to carry light rail, they did have to bolster many portions of the bridge beyond what they initially thought: post-tensioning pontoons to carry more weight; seismic upgrades to ensure the bridge won’t spill the train into Lake Washington during a seismic event; and making sure none of the electric current from the trains goes arcing into the bridge itself.

It turns out our region’s booming growth also plays a factor. All those cranes we see around town means busy contractors, and higher labor costs to secure specialized workers for the I-90 job.

What many may have not heard before is that the windstorms may actually be the biggest challenge to the East link light rail segment over the bridge. A strong enough wind will bring the trains to a halt.

“We did find that in events where there are storms, where there is sustained high winds, we will back off on light rail operations,” Lewis said. “At present, we are looking at about a 35 mile per hour sustained wind from the north when we would operate one train at each time, in each direction on the bridge. If winds get up to the 40-50 mile per hour range, both trains will come off the bridge.”

The south side of the bridge would somewhat shield the track from both the wind and the waves that could spill into a train should the wind come from that direction. But still, Lewis acknowledged we’ve all seen this type of weather.

“If you have been on any of the floating bridges when you have storm event that has churned for a long time, and has the lake rocking, and you have white caps and wave action providing a spray onto the roadway, that is the kind of action we are talking about,” he said. “It’s not a frequent occurrence.”

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With all the cost of retrofitting I-90, should we have built an entirely separate bridge for the light rail? Lewis said no. That wouldn’t have likely saved any money.

Taking a step back and looking at the big picture, beyond the East Link light rail line, Lewis thinks we made the right choice of building light rail in the region.

“When you look at what light rail is going to bring this corridor, and I’m sure you’ve traveled this corridor, particularly during the peaks and experienced the traffic congestion,” Lewis said. “Light rail is going to be operating in its exclusive right of way, which means when we are on the bridge we are operating in our desired speeds as opposed to some of the traffic on the adjacent roads.”

Which brings up the question of capacity. Are those trains going to carry enough people to justify their cost? The plan is to start with two or three trains, but at max capacity, they can run four trains every eight minutes.

“We’re looking at about 6,000 passengers per hour, per direction in a four-car train; we have capacity for that,” Lewis said. “Back in the day when I was doing my traffic engineering classes out of the university, it was 2,000 cars per lane, per hour. But the capacity of light rail and the potential it offers not only in capacity but also in travel speeds — that’s really the penalty in the I-90 corridor right now because of the level of congestion. We’ll be out of that congestion.”

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So light rail can carry 6,000 people each way per hour. And the traditional lanes, all three of them, can carry about 6,000 cars each way per hour. Numbers to strictly compare cars to the light rail trails were not readily available.

The East Link extension is projected to be completed by 2023.

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