Interstate Bridge crossing the Columbia River towards Oregon
Beginning with the section about 3 miles (5 km) north of the California border, the highway runs from 4,310 foot (1,314 m) Siskiyou Summit, the highest point on I-5, through Oregon's southern mountains and towns such as Ashland, Medford, and Grants Pass. Past Roseburg, the mountains tend to turn into hills, and as it reaches Eugene, the road enters the Willamette River Valley. At Eugene the highway intersects with the short Interstate 105. The interstate then heads almost due north, skirting near Albany and Corvallis, and passes through Salem. There were plans to build a spur into Salem, Oregon, called Interstate 305.
In the Salem area, placed in the median between mile marks 259 and 260 (closer to 260), is a sign designating where I-5 crosses the 45th parallel. It bears the words "45 Parallel half way between the Equator and the North Pole".
The highway then tracks a little to the northeast, splitting off Interstate 205 south of the Portland metro area. From here it passes up through Tualatin and Tigard along former U.S. Route 99W before hitting the southern terminus of I-405 and the Marquam Bridge. Also planned was a spur in Portland off of I-405, called Interstate 505, but it was never built and has been removed from city plans. A stub of I-505 exists as a long exit ramp to U.S. Route 30.
After crossing the Willamette River on the Marquam Bridge, I-5 has junctions at the western terminus of Interstate 84 and the northern terminus of I-405. It then continues through the northern parts of the city of Portland, and crosses into Washington via the Interstate Bridge.
Notably, bicycles are not prohibited from most of I-5 in Oregon, perhaps because in rural and mountain areas, few or no alternate routes exist (having been largely built over the alignment of U.S. 99, which in many places was laid over historic trails). In the early 1970s, restrictions against nonmotorized vehicles began appearing in denser urban areas where such use would be unsafe, but, as of April 2007, the rest remains accessible. [1]
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