The first section, from Crewe to Chester, was built by the
Chester and Crewe Railway and absorbed by the
Grand Junction Railway shortly before opening in 1840. The remainder was built between 1844 and 1850 by the
Chester and Holyhead Railway Company as the route of the Irish Mail services to
Dublin. The line was later incorporated into the
London and North Western Railway. Between Chester and
Saltney Junction, the line was, from the start, used by trains of the
Shrewsbury and Chester Railway, later to be incorporated into the
Great Western Railway. So important was the line in the 19th and early 20th centuries to passenger, mail and freight traffic between Britain and Ireland that the world's first experimental and operational
water troughs were installed at
Mochdre, between Colwyn Bay and Llandudno Junction. Their purpose was to enable steam engines (especially on the Irish Mail) to collect water without stopping. Later, considerable stretches of line between Chester and Colwyn Bay were quadrupled to increase line capacity, but these sections have now been reduced to two tracks.
Modern day In 2018, a £50 million signalling upgrade programme was completed between Shotton and Colwyn Bay. This upgrade saw modular colour lights supervised from the South Wales
Rail Operating Centre in Cardiff replacing the manual signal boxes and mixture of semaphore and older colour lights. ==Main calling points==