Traffic Lab is a Seattle Times project that digs into the region’s transportation issues to explore the policies and politics that determine how we get around and how billions of dollars in public money are spent.

A work-zone closure of northbound Interstate 405 in Kirkland, to dig a stream culvert below the freeway lanes, is vexing traffic so much that the state closed the ramp Saturday afternoon from westbound Highway 520 to northbound I-405, so cars won’t pour into the congested area.

Despite warnings and the belated ramp closure, freeway lanes were still stop-and-go at 8 p.m. Saturday, from the 520/I-405 junction in Bellevue all the way through Kirkland.

All northbound I-405 lanes are closed from Northeast 70th Street to Northeast 85th Street from 11 p.m. Friday, Aug. 28 until 5 a.m. Monday, Aug. 31.

And now, the ramp coming in from westbound 520 is closed from 3 p.m. Saturday until 5 a.m. Monday, the project team announced.

“Travelers should expect miles-long backups,” the Washington State Department of Transportation warned beforehand. Previous weekend jobs there have generated 1- to 3-mile clogs, even spilling into Highway 520.

Just north of this work zone, three of the five northbound lanes will close for 1 mile so workers can repave I-405 while northbound traffic is crimped upstream.

Traffic can still enter I-405 via the Northeast 85th interchange’s surface roundabouts for trips north to Bothell and Lynnwood or south toward Bellevue.

Contractors will dig a trench this weekend, similar to a weekend dig that closed southbound lanes in July, as the state extends a tiny Kirkland creek. Similar jobs have interrupted I-405 travel in Renton or been bundled with other lane construction.

It’s one component of the state’s triple-layer interchange project at 85th to create a Sound Transit bus-rapid stop and express toll lane ramps. It’s expected to be done this winter, said Washington State Department of Transportation spokesperson Julie Moon.

Eastside delays on I-405 will be compounded by the ongoing repave of two I-5 lanes at Seattle’s Ship Canal Bridge, which limits regional capacity.

Also this weekend:

The busy ramp from southbound I-5 to southbound I-405 in Lynnwood will close Sunday from 6 a.m. until 6 p.m. for roadway repairs.

Midday and evening delays are expected at Colman Dock in Seattle, affecting service to Bremerton and Bainbridge where Washington State Ferries has closed one boat slip for repairs.

One lane of southbound I-5 at the Albro Place/Swift Avenue overpass in Seattle will close Sunday from 5:30 to 9:30 a.m. for a bridge inspection.

Southbound I-5 in Dupont, next to Joint Base Lewis-McChord, will be reduced to three lanes from 9 p.m. Friday until 4:30 a.m. Monday to reroute drains and paint temporary lane stripes. WSDOT warns weekend drivers to expect 20-minute delays.

Sounder gameday trains will go to the Sounders match set for 1:30 p.m. Saturday against the Chicago Fire. The S Line leaves Lakewood Station at 10:11 a.m., while the N Line leaves Everett Station at 10:45 a.m., serving all stops between those points and Seattle’s King Street Station.