Complex sentence: Railway technology advanced, and in the 1840s railways using steam locomotives and running longer distances were being planned and built, and in 1845 the North British Railway purchased the line, using it as a springboard for its line to Carlisle.
Split into simpler sentences: Railway technology advanced, and in the 1840s railways using steam locomotives and running longer distances were being planned and built. In 1845 the North British Railway purchased the line, using it as a springboard for its line to Carlisle.