The traditional commute for I-90 drivers working in Seattle got tougher, and the reverse commute to the Eastside quicker, in the first week after express lanes closed.

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In the first week without Interstate 90 express lanes, the traditional commute to and from Seattle took longer, while reverse commutes to and from Eastside jobs improved.

So says INRIX, the international traffic-data company based in Kirkland, after crunching its own numbers.

Severe congestion, reflecting slower speeds and longer travel times, appeared across Mercer Island in the morning drive westbound.

In the evening, cars took longer to leave Seattle and reach the Eastside, chief economist Bob Pishue reported Thursday.

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I-90’s westbound morning trips took four to seven minutes longer between 8 and 9 a.m. on June 5-8 compared with April, Pishue found. But eastbound the drive was four to seven minutes quicker.

The I-90 center express lanes, which carried carpools, buses and Mercer Island drivers, permanently closed this month to make room for construction of Sound Transit’s light rail across Lake Washington, to open in 2023 and haul an estimated 50,000 daily riders. To compensate for road loss, crews squeezed new high-occupancy lanes into the freeway mainlines, which reduced shoulders and lane width.

Pishue suggests that the Washington State Department of Transportation (WSDOT) continue to keep incident-response teams nearby to quickly clear stalled or crashed vehicles and keep traffic moving.

“A minor accident could bring a pretty big ripple effect,” he said, because stalled vehicles may just have to stay and block a lane.

A June 9 crash eastbound midlake at noon slowed other traffic 10 minutes, and delays lingered past 1 p.m., even though the shoulders there are a relatively generous 8 feet.

WSDOT isn’t reporting new travel times yet. Historically, traffic requires six months to settle into a long-term pattern, after bridge or toll-lane projects.

“We’re still expecting things to shake out further. It’s early at this point to draw conclusions,” said WSDOT project spokeswoman Annie Johnson. “Anecdotally, the Seattle to Eastside commute in the mornings has gotten a little bit better, that’s what we’ve heard from the folks.”

The pattern largely fits government traffic studies, which touted the value of adding a reverse-commute lane for buses and carpools. But early facts also support critics who worried about tie-ups through Mercer Island, though traffic jams didn’t overflow into the tiny downtown as feared.

One vulnerable place is the Rainier Avenue merge to the eastbound Mount Baker tunnel, which became more abrupt — and where one 10-foot lane and one 10.5-foot lane replaced a wider single lane in the right tunnel passage. At times, Rainier-area traffic jams spilled onto I-5 in the afternoons.

An INRIX congestion scan for June 7 shows speeds under 30 mph in the afternoon at the eastbound Mount Baker tunnels, and also slow in the morning westbound at mid-Mercer Island. The data include a mixture of general and high-occupancy lane traffic.

The company has long experience collaborating with the state, and INRIX recently won a contract to monitor road networks in 50 states for the Federal Highway Administration.

The data from last week is a limited sample, and the company has a history of encouraging road expansions. But the report doesn’t attempt to make political points.