If I-90 drivers had carpooled more, we wouldn’t be in this mess

We’ve all heard by now about the $220-million-plus cost overrun to extend Sound Transit’s light rail system over the I-90 bridge to the Eastside.

RELATED: East Link wants kudos for being on budget?

Frustrating — but certainly not the first massive construction project to give us a surprise like that.

But what is new is the project itself — building a light-rail line over a floating bridge. That’s never been done anywhere in the world before. Which is what makes this expensive.

I sat down with East Link Executive Director Ron Lewis to discuss where exactly all those cost overruns are coming from, and also to understand why this is considered the best way to move people.

Many of you remember being told that the new I-90 bridge was designed from the beginning to carry light rail — but it turns out that isn’t 100-percent true. The concrete pontoons will have to be reinforced by stringing steel reinforcement cables the length of the bridge to carry the extra weight.

Sound Transit had to design a custom-built flexing system to carry the trains from the fixed part of the bridge to the floating part. And they’ll need a system to prevent stray electric current from deteriorating the bridge.

At the same time, the building boom in Seattle means it’s also more expensive to hire construction workers.

However, Lewis says that even though the I-90 portion is over budget, the six other parts of the East Link project are either at or under budget.

So even with the overrun on the bridge, he told me that the whole $3.7 billion East Link extension, which branches from the station in the International District, across I-90, through Mercer Island and Bellevue, and into Redmond, is still within its budget.

So that sounds like good news.

But I was surprised by something else he told me: The expected effect of windstorms on light rail service.

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

The problem is that when the north wind is strong enough that waves start breaking over the bridge, the bridge moves too much to run trains safely, even if you can still drive a car across.

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

And he says the main problem is only with winds from the north, which is relatively rare. A south wind would have to hit at 50 mph before trains would be affected.

But the bottom line is that trains would have to be stopped in weather that cars can handle.

Other I-90 options?

So I asked Lewis: Given how much it’s costing to prepare this bridge which was supposed to be rail-ready, wouldn’t it have been cheaper just build a separate bridge designed for rail from the ground up?

He said no.

So I asked him if using the 520 bridge would have been a better bet. It was built as weather-resistant, after all.

Lewis argued that it isn’t like the I-90 bridge is just sitting on the water.

So then — big picture time — was light rail the right choice?

“When you look at what light rail is going to bring to this corridor — especially during traffic congestion — light rail will be operating in its exclusive right of way, which means when we’re on the bridge, we are operating at our desired speeds, as opposed to traffic on adjacent roadways.”

The trains will always run at 55 mph, no matter how bad traffic gets. Unless it’s a really windy day.

But I wanted to see some numbers. Will the trains carry enough people to justify their cost?

At max capacity, they can run four trains every eight minutes. Here’s how it breaks out.

“We’re looking at about 6,000 passengers per hour, per direction on a four-car train …,” Lewis said. When he was taking traffic engineering classes, it was 2,000 cars per lane per hour. “But the capacity of the light rail and potential that it offers not only in capacity but in travel speeds, that’s really the penalty that there is in the I-90 corridor right now because of the level of congestion.

“We’ll be out of that congestion.”

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.

But if people carpooled with at least three people per carpool, each track of the light rail system would carry the equivalent of one carpool lane.

If only we had we all just carpooled a little bit better.

The East Link extension of Sound Transit is projected to be complete in 2023.

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