Complex sentence: The route was extended northward to Plainview in 1950 and into Swisher County to, in 1953; the latter created the concurrency with, which TxDOT officially considers a gap in that route's mileage.
Split into simpler sentences: The route was extended northward to Plainview in 1950. That same year, it extended north to; this created the concurrency with, which TxDOT officially considers a gap in that route's mileage.