"Over the Beaverton-Tualatin Highway from its junction in Beaverton with the Beaverton-Tigard Highway, OR217, southerly on SW Hall Boulevard to its westerly junction with SW Durham Road in Tigard. Also over the Beaverton-Tualatin Highway from its easterly intersection with SW Durham Road at SW Upper Boones Ferry Road in Tigard, southerly on SW Upper Boones Ferry Road and SW Boones Ferry Road via Durham to the south end of the Tualatin River Bridge in Tualatin. Also over the Beaverton-Tualatin Highway from its intersection with Norwood Road in Tualatin, southerly on SW Boones Ferry Road to the Stafford Road Interchange at Pacific Highway, I-5, in Wilsonville."
~ ODOT, Descriptions of US and Oregon Routes, March 2007
OR-141 was designated along stretches of Hall Blvd., Durham Rd., and Boones Ferry Rd. in August of 2003, one of the newest in Oregon's recent wave of creating route designations along stretches of unmarked state highways. The route's number comes from ODOT's secret designation of its associated state highway, the Beaverton-Tualatin Highway #141. While the OR-141 designation is new, this highway did at one time have a different route attached to it. From the 1930's to around 1972, this highway was designated as OR-217, running along the then-Beaverton-Aurora Highway #141 between downtown Beaverton and Aurora; this highway predated the almost-parallel Wilsonville-Hubbard Highway #51 (now OR-551). Once a freeway was completed in 1972 between US-26 in Cedar Hills and I-5 in Tigard, it was given the OR-217 designation, removing it from the Beaverton-Tualatin Highway #141.
What is peculiar about OR-141's routing is that it is not designated along any city-maintained roadways, making it extremely discontinuous; it was routed over remaining segments of the Beaverton-Tualatin Highway. The only way for motorists to know that they're even on the highway is by noticing the mileposts on the side of the road, which are marked surprisingly well for a highway broken up by jurisdictional transfers; some even remain on city-maintained stretches. This is evidenced by the official route designation, displayed above. Since it is not signposted in the field, OR-141's segmented designation is quite superfluous and, in my opinion, quite ridiculous. The Beaverton-Tualatin Highway #141 has had jurisdictional transfers ever since the OR-217 freeway was built. In 1979, its northern end was shortened, first the portion from OR-8 in Beaverton to Allen Rd. in March, followed by the August elimination from Allen Rd. to the south Beaverton city limit (its current northern terminus. Then, in February 1997, the Durham Rd. section was transferred out of state maintenance. Finally, in August 2002, the portion of Boones Ferry Road from Norwood Rd. through Tualatin to the southern end of the Tualatin River Bridge was transferred to Tualatin city maintenance. I personally think it's only a matter of time before the entire route gets written into ODOT's history books, possibly taking the OR-141 designation with it.
MILE 3: The Mile 3 milepost heading Northbound along OR-141 is very peculiar; it looks like a typical Oregon milemarker, except with an overlarge "3" in FHWA Series C type and with no white border. The fact that it doesn't have the border makes it look especially strange, probably stranger than it would look with the border on it. My guess is that this milepost was placed by the City of Tigard, because it certainly doesn't look like any other milepost I've ever seen. You can see a graphical rendition here.
MILE 5: Just before milepost 5, you'll see some old faded button copy BGSs at the junction with OR-99W. These were probably in place back when this road was OR-217, even though they use shields for OR-99W, which didn't become so until 1972.
FORMER MILE 11: There's a MILE 11 milepost along this section of Tualatin-Maintained former highway. This milepost is one of the few remnants of when this stretch was state-maintained.