Complex sentence: In 1961, during the electrification of the line, new single-line tunnels were built parallel to the existing double-line Loreley and Rossstein tunnels and the old tunnels were then converted to single-line operations and electrified.
Split into simpler sentences: In 1961, during the electrification of the line, new single-line tunnels were built parallel to the existing double-line Loreley and Rossstein tunnels. The old tunnels were then converted to single-line operations and electrified.