Complex sentence: The highway is primarily a two-lane road between Benton City and Richland, however the road expands to three, then four lanes wide in West Richland, which the highway remains as to its terminus in Richland.
Split into simpler sentences: The highway is primarily a two-lane road between Benton City and West Richland. The road expands to four lanes in West Richland, a width the highway remains to its terminus in Richland.