Hillsboro residents who commute through Portland on Interstate 5 have less than a month to plan for a major disruption: all southbound I-5 lanes will shut down between Interstate 405 and Interstate 84 in the Rose Quarter starting Friday, Sept. 11, for up to five weeks.

The closure affects roughly 120,000 vehicles per day, according to the Oregon Department of Transportation. ODOT warns drivers to expect commute times two to three times longer than normal on the affected stretch, with congestion spilling onto local Portland streets and potentially backing up across the Columbia River into Washington state.

"Even if you don't use I-5, your travel may be affected by the temporary changes in traffic patterns as people use alternate routes and different ways to get around," ODOT Project Delivery Manager David Kim told KATU on Aug. 14. "So you might want to plan ahead and give yourself extra time."

The shutdown runs around the clock.

Why the closure

Crews will tear out and replace deteriorated concrete on the elevated highway structure just south of the Moda Center. ODOT says the surface was last replaced in 1985. The 1.8-mile section is the only two-lane stretch of I-5 in a major urban area between Canada and Mexico, carries the highest crash rate of any urban interstate in Oregon and is the state's top traffic bottleneck.

The work is Phase 1A of the I-5 Rose Quarter Improvement Project, which carries a $75 million price tag for this initial phase. The full project is estimated at $1.96 billion to $2.08 billion, with funded construction expected to wrap by the end of 2029, OPB reported.

ODOT chose the five-week full closure over alternatives that would have meant single-lane closures lasting four months or weekend-only closures stretching over two years.

Detour routes for Washington County drivers

ODOT's official detour sends local traffic onto I-405 southbound. Regional drivers heading farther south should use I-205 to bypass central Portland entirely.

For Hillsboro commuters specifically, the practical route is US-26 east to I-405 south. Those making longer regional trips can take I-205.

I-5 northbound remains open throughout the closure. I-84 westbound to I-5 southbound also stays open, and one lane to the Broadway/Weidler exit will remain accessible for local and event center traffic.

MAX Blue and Red lines: a Hillsboro alternative

TriMet's MAX Blue Line runs directly from Hatfield Government Center in downtown Hillsboro to Portland City Center, with trains every 15 minutes or less most of the day. The Red Line, boarding at Hillsboro Airport/Fairgrounds station, shares the same tracks through downtown Portland to Rose Quarter Transit Center.

Both lines are unaffected by the road closure. TriMet completed its Westside MAX Improvements project on Aug. 9, restoring full Blue and Red Line service on the west side well before the Sept. 11 shutdown begins.

Riders can plan trips at trimet.org or call TriMet Customer Service at 503-238-7433 on weekdays, 7:30 a.m. to 5:30 p.m.

The closure begins Sept. 11. Drivers can sign up for travel alerts at i5rosequarter.org or check conditions at TripCheck.com. ODOT says crews will work around the clock and reopen the interstate as soon as repairs are finished.