Aug. 15—Long ago, The Onion published this famous headline next to a photo of clogged traffic in Kirkland: "Report: 98 Percent of U.S. Commuters Favor Public Transportation For Others."
That joke contains a kernel of truth.
Many people assume transit is supposed to fix gridlock. Sound Transit's first winning tax campaign in 1996 appealed to drivers by proclaiming "the problem is traffic congestion," while a federal transit administrator in 2003 exaggerated the initial Seattle-Tukwila line's benefits by comparing it to seven highway lanes. Meanwhile, opponents argued this month that Sound Transit should be held accountable for delivering "little or no impact on road congestion or carbon emission reductions."
Can light rail, and especially the $3 billion Northgate-Lynnwood extension that opens Aug. 30, fix what ails adjacent Interstate 5?
Sound Transit's new 8 1/2 -mile line won't make the freeway significantly faster, partly because many customers will be former bus riders, not just former drivers. But the option for motorists to switch to trains should provide a lifeline to thousands discouraged by crushing delays. The 30% of the population who don't drive will gain freedom to travel more often.
I-5 traffic snarls, already seeping toward Lynnwood before 2 p.m., would become worse without new rail capacity, some local experts predict. That's especially true in 2025 and 2026, when reconstruction of worn-out I-5 decks will block three lanes in North Seattle.
Limited research exists to tell us how the new Lynnwood Link might affect congestion. Variables like new apartments, rising populations, parking fees, transit quality and the evolution of work-from-home jobs in the 2020s tilt the data.
Most of all, there's the phenomenon of induced demand. Whenever somebody ditches their car to ride transit, someone else notices more space to drive, as if a new lane had been built. And when freeways expand, car-oriented uses develop, such as warehouse stores, isolated tracts of big homes or drive-thru eateries.
"Even though Link has done a lot in capturing trips, it doesn't mean I-5 works better. There are more trips out there," said Mark Hallenbeck, retired director of the Washington State Transportation Center at the University of Washington.
Congestion is roaring back postpandemic
Fresh data from March to June shows an average weekday trip time of 36 to 39 minutes during the morning rush from Lynnwood to Seattle and 40 to 43 minutes in afternoons, compared with 17 minutes in free-flowing traffic. Trips reach an hour during certain busy times. To be sure of arriving on time, solo drivers need to allow 90 minutes, and bus riders 60 minutes, said Roger Millar, state transportation secretary.
By contrast, light rail will cruise from Lynnwood to U District Station in 21 minutes, or to Symphony Station downtown in 33 minutes, unless there's some blockage or outage.
A matter of scale
Even full trains can't cure congestion because each rail line only serves as one spoke in a vast metropolitan region.
About 1.7 million households make 15.8 million trips of all kinds daily in Snohomish, King, Kitsap and Pierce counties, according to Puget Sound Regional Council surveys. The 24-mile line between Northgate and Angle Lake currently serves 78,500 passengers per day, a count the Lynnwood extension should raise to between 100,000 and 136,000, this year's service plan says.
That's still only 1% of regional travel
The Sound Transit 3 tax measure, passed by voters in 2016, promised light rail to Everett, Tacoma, Issaquah, West Seattle and Ballard, three bus-rapid transit lines and more Sounder commuter train service that planners said would serve 750,000 daily passengers by the 2040s.
Even if Sound Transit meets its targets, it's fanciful to think traffic would ebb, so long as growth and prosperity continue.
"If you're looking at where you don't have congestion, it's in failed economies," said Millar.
"There's always going to be congestion on the highway, but if you choose not to drive yourself in an automobile, here's an alternative that gets you where you're going, perhaps gets you where you're going faster," Millar said.
Charles Prestrud, transportation analyst for the free-market Washington Policy Center, observes that light rail through Rainier Valley to SeaTac hasn't made a perceptible dent in traffic delays, where I-5 clogs all day near Boeing Field. "Not enough people are drawn out of their cars to make a difference in crowded conditions," he said.
Switching rides
Sound Transit's 2024 service plan predicts 25,300 to 34,200 daily boardings in the four new stations, and if you count return trips, that's a total clientele of roughly 50,000 to 70,000 riders, to increase by the 2030s.
Of those trips, about 30% will be new riders who wouldn't ride existing transit, said spokesperson John Gallagher. Some will be former drivers, a market encouraged by 3,800 park-and-ride stalls. Others will be new kinds of trips, such as young adults who can ride 29 minutes to a Capitol Hill concert, half the former trip time.
Thousands of customers who transferred from buses to trains at Northgate Station, especially University of Washington students, will hop onto light rail farther north. Community Transit is overhauling its bus lines so they constantly deliver people to trains in Lynnwood and Shoreline and quit going into Seattle.
Total travel will increase again when the trackways across I-90 to the Eastside's 2 Line are finished (in late 2025 or early 2026), bringing more trains into North Seattle and Lynnwood, Sound Transit expects.
Thousands of future apartments and town homes, where cities rezoned land next to stations, should stoke demand.
How congestion works
On mainline I-5, saturated up to eight hours a day with 205,000 cars, traffic teeters on the brink, at volumes 20% beyond its design capacity. A surge of cars, or drivers who suddenly swerve and brake, can degrade flow from the ideal 2,000 vehicles per hour per lane to 700 or worse.
Hallenbeck likens sudden traffic collapse to the cartoon character Wile E. Coyote, who sprints after the Roadrunner before dropping off a desert cliff.
Subtracting a few thousand daily car and bus trips may improve I-5 slightly at the margins, Hallenbeck said. Midday snarls wouldn't begin until later in the afternoons, for instance.
"If you were to take all of those trips in Sound Transit and put any fraction of them on the freeway, life would be way worse," he said. That's obvious when sports events bring less traffic into Sodo because many ride transit, he said.
Even Prestrud agrees that rail offsets some Sodo traffic but emphasizes that's hardly a reason to spend $148 billion from 2017-46 to build and operate Sound Transit, compared to cheaper bus-rapid transit and telework investments.
Population growth is expected to add both drivers and transit riders. The regional council anticipates 1.5 million new residents by 2050. If very many drive from Lynnwood into Seattle, all-day slowdowns are likely, Hallenbeck said.
Congestion relief is notoriously hard to predict.
Highway vehicle counts in the Denver area increased 31% next to new light rail lines from 1992-2010, compared with 41% on nearby freeways, suggesting "some impact on highway traffic growth," two scholars reported.
When Manchester, England, built six light rail lines in 1990, transport officials were surprised to find 3.3 million car trips per year converted to light rail and 2.5 million other "new" trips.
In a real-life alternate universe, Los Angeles experienced a 47% surge in road congestion during a sudden transit workers strike in 2003, a study found.
Todd Litman, founder of the Victoria Transport Policy Institute, said it's possible for new transit to improve speeds up to 10 mph, permanently, on parallel freeways. That's because people are less willing to join the highway snarls if frequent, safe and unobstructed transit is nearby, he said.
Lynnwood Link's environmental impact statement in 2015 speculated that 300,000 fewer miles a day will be driven north of Northgate, as some motorists change to rail. This would "slightly reduce vehicle volumes or congestion in the corridor." The total number of people moved, by roads plus transit, would increase 10%.
Would the freeway refill?
Light rail "will definitely release the traffic congestion and delay north of Seattle," said Yinhai Wang, the new transportation-center director at UW. "However, just like [on] newly constructed roadways, induced traffic will grow with the years to come."
For perspective, new highway lanes become 60% to 90% full within three to five years, Wang said. (The Washington State Department of Transportation has no immediate intent to widen I-5, but Millar said Lynnwood Link's tracks were positioned on the edge of WSDOT land, keeping space for limited lane additions.)
Losing three lanes
All the prognostications will fail in 2025 and 2026, when WSDOT embarks on a long-awaited I-5 redecking project that will block three lanes during most months.
New concrete surfaces on I-5 across the Ship Canal Bridge and viaducts alongside Capitol Hill, plus asphalt ramp repaves around Roosevelt and Northgate, will require lane closures of 110 to 130 days at each work zone. The $203 million contract also allows 12 weekend closures of all southbound lanes and four northbound.
Contractors will fix the northbound side first. By the time southbound I-5 closures hit in 2026, Sound Transit's overdue track segment across I-90 should be finished, so Eastside trains will alternate with Seattle-SeaTac trains in Lynnwood, enabling departures every five minutes, instead of eight to 10 minutes apart this year.
The full picture
Sound Transit toned down its rhetoric years ago and doesn't explicitly promise a faster freeway drive. Video speaks loudly, however, and the most recent expansion campaign in 2016 highlighted a packed I-5.
"That was one of the selling points of the system," Prestrud said. "Are they going to move the goal posts, once they've spent tens of billions of dollars?"
By the late 2010s, when new Capitol Hill and University of Washington stations attracted 40,000 more daily riders, then-CEO Peter Rogoff emphasized "the opportunity to escape congestion."
Transit capacity will attract more trips, like new freeway lanes attract traffic, Wang said. Light rail can indeed carry 7,200 people per hour between Snohomish and King counties, or enough to fill three freeway lanes, if trains depart every five minutes someday.
But those high figures would be for full trains. You don't want railcars constantly maxed out in Shoreline because people still need to get on at Roosevelt.The trade-offs between congestion, transit and land use aren't always obvious.
Hallenbeck mentioned five newer 22-story buildings in the University District whose residents travel mainly without cars and often on Link. Those tenants would otherwise live in suburbs where driving is more necessary and aggravate regional congestion, he said.
"The other thing that we're paying attention to right now is that at least one-third of the local population doesn't drive," Millar said. "They're too young, they're no longer able, they're not willing or we won't let them."
Congestion relief is just one yardstick to measure the reach of light rail.
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