Complex sentence: The rail line that the highway parallels between Toppenish and just west of Prosser has existed since at least 1910, originally belonging to the Spokane, Portland and Seattle Railway, is now part of BNSF Railway as part of their Yakima Valley Subdivision.
Split into simpler sentences: The rail line that the highway parallels between Toppenish and just west of Prosser has existed since at least 1910. It originally belonged to the Spokane, Portland and Seattle Railway, and it is now part of BNSF Railway as part of their Yakima Valley Subdivision.