Pacific Highway (United States) from the Hudson's Bay Company were the first non-Native Americans to use the route of the future Pacific Highway to move between today's Washington State and "Alta California." During the second half of the 19th Century, mule trains, stagecoaches, and the Central Pacific Railroad also followed the route of the Siskiyou Trail. In the early 20th century, around 1910, entrepreneur Sam Hill lobbied the governments of Washington and Oregon to build automobile roads along the path of the Siskiyou Trail, with the ultimate goal of building a paved auto route from Canada to Mexico. Pacific Highway (United States) Pacific Highway
Washington State Route 510 also became (I-5) in 1968. SR 510 between I-5 and Pacific Avenue was reconstructed and widened in late 2003, with the addition of a roundabout at the Pacific Avenue intersection. The I-5 interchange will be replaced in 2020 with a diverging diamond interchange that began construction in October 2018. The interchange will be the first diverging diamond constructed in Washington and is estimated to cost $72 million, with funding provided by the state legislature's 2015 Connecting Washington package. State Route 510 Alternate, also known as the Yelm Loop, is a partially completed bypass of Yelm. The first, section opened to