Construction of an electric substation will shrink four-lane Denny Way to two lanes until mid-November, causing gridlock at South Lake Union.

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Denny Way, a crowded crossroads at the edge of downtown Seattle, will be reduced to one lane each direction, for the next five weeks.

The road, which carries more than 23,000 vehicles a day, will operate with one lane each direction, 24 hours a day, until Nov. 21, the city estimates.

A city alert warns: “Seattle City Light encourages drivers to avoid the Stewart Street exit from I-5 during this time.” The work zone on Denny runs from Stewart to Minor Avenue, about two blocks.

Access will be kept from Denny to the Yale Street onramp to southbound I-5, but getting there will take longer than normal, according to the Seattle Department of Transportation.

Mercer Street may get more congested, as drivers avoid the chokepoint. The King County Metro Transit 8 bus on Denny to Capitol Hill, already known as the “Leight” for being behind schedule, is certain to lose time. Traffic gridlock might block Route 70 to Eastlake, and maybe the RapidRide C, Metro Route 40 and the South Lake Union streetcar out on Westlake Avenue. People walking should be vigilant, as fed-up motorists move off Denny into the side streets.

The shutdown will make room for construction equipment, vehicles and workers to build the new Denny electrical substation for the booming South Lake Union area.

Commuters and travelers across the north end will be supporting the growth of e-commerce, biotech and housing enterprises through time they spend in the extra traffic delay — especially if gridlock spreads to thousands of buses and cars on Stewart Street.