(Burlingame to Portland; Hwy #1W MP 3.05-0.85, 2.19 miles)
"Over the Farmington Highway from its junction with the Hillsboro-Silverton Highway, OR219, approximately five miles south of Hillsboro, easterly via Farmington and Hazeldale to the junction of Southwest Farmington Road in Beaverton; thence easterly over Southwest Farmington Road to its junction with Beaverton-Hillsdale Highway; thence easterly over the Beaverton-Hillsdale Highway via Hillsdale to its junction with the Pacific Highway West in Portland; thence northerly over the Pacific Highway West to its junction with the Mt. Hood Highway, US26 in Portland."
~ ODOT, Descriptions of US and Oregon Routes, March 2007 (this definition has not changed since US-26's rerouting around Portland)
OR-10 was designated at the inception of the Oregon state route numbering system in 1932 along the Beaverton-Bertha Highway #40. The route was designated from the Tualatin Valley Highway #29 (then OR-47, now OR-8) in Beaverton along Broadway, crossed old OR-217 (now Hall Blvd.), then traveled another 5½ miles or so to the West Side Pacific Highway #3 (then US-99W). In 1937, the West Side Pacific Highway and US-99W was realigned to Barbur Blvd., and OR-10 was extended along a 0.87 mile stretch of the old West Side Pacific Highway (called the Capitol Highway); as a result of the extension, OR-10 was then called the Beaverton-Hillsdale Highway #40. OR-10's route then pretty much stayed the same for 45 years, until a 1982 Beaverton traffic flow redesign project got rid of a railroad through town. This project upgraded a connection between Farmington Rd. (then OR-208) and OR-10, resulting in OR-208 to be replaced by OR-10 along all of Farmington Rd. within Beaverton and the Farmington Highway #142 outside of Beaverton; OR-208 was retired. Around or before this time, OR-10 was also added along the Pacific Highway West #1W (OR-99W) from Burlingame to Portland, terminating at the junction of the Pacific Highway West and the Sunset Highway #47 (which carried the US-26 designation until 2005); when OR-99W was scaled back to Tigard in the 1970's, OR-10's designation remained. Most maps and BGSs still only show OR-10 along that stretch, even though OR-99W was reinstated up until where OR-10 ends in Portland at the former junction of US-26.
Interestingly enough, only 6.51 miles of OR-10's length is under state maintenance, down from 7.64 miles when I first wrote this page. The termini of both the Farmington Highway #142 and the Beaverton-Hillsdale Highway #40 have been trimmed. The Farmington Highway's state maintenance now begins at SW 198th St. in the outskirts of Beaverton and ends at SW 170th St. within the Beaverton city limits, plus a 0.06 mile section between SW 149th and SW 148th Sts.; the portion from OR-219 to SW 198th St. was dropped in July 2003, the portion between SW 170th and SW 149th Sts. was dropped in March 2003, and the portion east of SW 148th St. was transferred in August 1979 (Cedar St. to the Beaverton-Hillsdale Highway) and April 1980 (Beaverton city limits to Cedar St.).
The Beaverton-Hillsdale Highway now begins at its junction with OR-217 and ends at the Washington-Multnomah County line; the stretch beyond the county line was transferred over to the city of Portland on July 21st, 1992, and the portion from OR-8 to OR-217 was transferred sometime in the late 1970's/early 1980's. All of OR-10's duplex with OR-99W is, however, under state maintenance. US-26 used to be cosigned with OR-10 and OR-99W for less than a mile, but since it was moved onto I-405 and city streets between the Vista Ridge Tunnel and the Ross Island Bridge in 2005, a semi-direct grade-separated interchange is the only US-26 connection.
What was OR-10 between 1932 and 1982 is still completely intact and is shown in red. This portion of the Beaverton-Hillsdale Highway is no longer under state maintenance and is also no longer a direct route into Beaverton; one must make a right turn off of the Beaverton-Hillsdale Highway to take the route.