Recent residential development in Maple Valley and surrounding areas has increased traffic congestion on the highway, leading to a series of widening and improvement projects funded primarily by city governments.

The highway continues north across the rural Enumclaw Plateau and past several gravel mines before beginning its ascent into the hills of Black Diamond.

It turns north at the southern boundary of Maple Valley, near a crossing of a railroad,[1] and travels through several suburban subdivisions near Tahoma High School.

The highway widens to five lanes in the city's Four Corners commercial center, where it intersects the eastern end of SR 516, which travels west to Covington and Kent.

[15] It follows the general route of the Columbia and Puget Sound Railroad, a branch of the transcontinental Northern Pacific Railway that was constructed in the 1880s to connect the area's coal mines to Seattle.

[24] A 2016 study of the corridor's safety by WSDOT concluded that the outdated design of the roadway had reached its capacity and was in need of immediate improvement to handle expected traffic volumes.

[9] An earlier WSDOT study recommended $300 million in projects to widen SR 169 to four or six lanes between Black Diamond and Renton.

[25] The Kummer Bridge was closed between November 2008 and June 2009 for an emergency reconstruction project after the discovery of major ground movement.