SR 99 was officially named the William P. Stewart Memorial Highway by the state legislature in 2016, after a campaign to replace an unofficial moniker honoring Confederate president Jefferson Davis.

Immediately north of the interchange, SR 99 turns east onto Pacific Highway and passes the Emerald Queen Casino, a gambling and hotel facility operated by the Puyallup Tribe, and a commercial district at the outskirts of Fife.

SR 99 then enters the city of SeaTac and continues north as International Boulevard, passing a federal detention center and light rail station on the southwest side of Angle Lake.

The freeway passes the corporate headquarters of Starbucks and Coast Guard Station Seattle before turning northeast to reach the southern portal of the Alaskan Way Tunnel near Lumen Field and T-Mobile Park.

[19] The highway turns northeast to follow the shore of Green Lake and passes through the residential districts of Phinney Ridge and Greenwood, where traffic signals replace the medians and right-in/right-out access.

[22] Near Shorewood High School and the Shoreline city hall, the highway is flanked to the east by the Interurban Trail and a park with a preserved section of the original North Trunk Road, which was paved in red bricks.

[37] The Bothell route was bypassed by a newer and straighter highway to the west that opened on October 9, 1927,[38] shortening the distance from Seattle to Everett by 3.8 miles (6.1 km) and featuring overpasses for the existing interurban and a gravel median strip in some sections.

[52] Railroad Avenue, later renamed Alaskan Way, was rebuilt in the 1930s as part of the federal government's improvements to the city seawall and became the primary bypass route for through traffic, experiencing major congestion as a result.

[59][60] The bypass viaduct gained popularity following the end of World War II and engineering work was approved in 1947, with construction funds sourced from the city and the Federal-Aid Highway Act of 1944.

[107][108] Sections of SR 99 in North Seattle along Aurora Avenue and in South King County declined economically after the opening of Interstate 5, losing businesses amid increased crime.

[110][111] The 17-mile (27 km) stretch from Federal Way to Tukwila in South King County, popularly known as the "SeaTac Strip", was where the Green River Killer (Gary Ridgway) picked up many of his victims in the 1980s.

[109][115] In southern King County, the cities of Federal Way, SeaTac, and Tukwila drew up redevelopment plans that were largely built out in the 2000s, reducing traffic collisions and crime while improving the area's appearance.

[130] In the aftermath of the crash and its three-year-long court case, WSDOT and the Seattle Department of Transportation have disagreed over whether to install a center barrier or median zipper system, and which agency would be responsible for funding either option.

[140] Four more closures were ordered later in March and April due to pieces of concrete dropping onto the streets below, requiring emergency repairs to add steel rods to reinforce the columns.

[144] Annual inspections and continued monitoring found that the earthquake had caused settling of up to 4 inches (10 cm) into the soil and weakened connections between the columns and highway decks.

[148][149] In late 2001, WSDOT began work on an environmental impact statement (EIS) for the viaduct replacement project using emergency funds from the state legislature and consulted the city government and community leaders to generate concepts.

[156][157] The six-lane, $4 billion tunnel option was chosen as the preferred alternative by WSDOT in late 2004, despite backlash from activists groups who favored a rebuilt viaduct or a waterfront boulevard.

[132] A pair of advisory, non-binding ballot measures was held in March 2007 to find a consensus between the $2.8 billion elevated replacement supported by Governor Christine Gregoire and a smaller four-lane tunnel with surface public transit improvements that would cost $3.4 billion and was supported by Mayor Greg Nickels; Nickel's "hybrid tunnel" proposal was rejected by Gregoire and state legislators prior to the vote based on operational and safety problems identified by WSDOT.

[162] The governments of Washington state, King County, and Seattle agreed to re-evaluate the planning process for the viaduct replacement and split the main proposals from essential safety and traffic improvements that would be included in all alternatives.

[132] A $915 million package of projects was approved for immediate construction, beginning with work to strengthen sinking columns in late 2007 and repairs to the Battery Street Tunnel the following year.

[165][166] The southernmost stretch of the viaduct, between Holgate and King streets, was demolished in October 2011 and replaced with a six-lane elevated freeway that opened the following year at a cost of $115 million.

[167][168] Seattle voters approved a bond measure in 2012 to replace the Alaskan Way Seawall;[169] the project began construction in 2013 and was completed in 2017 at a cost of $410 million, running 21 percent overbudget.

[40][178] On January 13, 2009, Governor Gregoire signed an agreement with Mayor Nickels and King County Executive Ron Sims to ratify the deep-bored tunnel as the replacement for the Alaskan Way Viaduct, to be completed by 2015.

[132] Neighborhood and environmental activist Mike McGinn was elected mayor in 2009, largely on an anti-tunnel platform, and threatened to veto project agreements until the state took responsibility for cost overruns that would fall upon Seattle.

[132][193] The Federal Highway Administration completed its analysis of the project's final EIS and issued its record of decision with WSDOT later that month, allowing pre-construction activities to begin.

[194] After the demolition of the viaduct's southernmost stretch and its lanes were realigned onto an adjacent bypass in 2012, crews began excavation of a 420-foot-long (130 m) launch pit to house the tunnel boring machine.

[201] Bertha reached the completed excavation pit in March 2015 and the machine's front end was disassembled and lifted to the surface to repair the damage, which was found to be more extensive than previously thought.

[214][215] The remaining 1.4-mile (2.3 km) section of the viaduct was demolished in stages between February and November 2019, with some of the 240 million pounds (110,000,000 kg) of rubble deposited into the Battery Street Tunnel as it was filled and sealed.

[228][229] A pair of granite markers were installed the following year in Blaine and Vancouver to commemorate the highway, allegedly to recognize Davis's contributions to the territorial development of Washington as U.S. Secretary of War.

[228] The bill was revived in May 2016 and was passed unanimously by both houses of the legislature, renaming SR 99 for William P. Stewart, an African-American Civil War veteran and early settler in Snohomish.