Line from Shrewsbury to Aberystwyth and Pwllheli, where the control centre was at Machynlleth. The future RETB is being gradually replaced with the new European in-cab signalling system, ERTMS. The Cambrian line was due to be changed over to the new system by spring 2010 but was delayed, being commissioned on 11 March 2011. The East Suffolk Line's system underwent life extension works in 2006, but was converted to conventional Track Circuit Block with axle counters in connection with increasing the service frequency to a point where the RETB could not have handled it. RETB was phased out on the East Suffolk Line after the last Ipswich-Lowestoft service arrived at Oulton Broad South on Friday 19 October 2012. RETB Next Generation Due to the loss of the Band III Sub Band 2 radio frequencies used by the NRN radio system from the digital TV spectrum reallocation the need arose for a system to replace RETB on two lines in Scotland - the West Highland Line and the Far North Line. The rugged terrain and light line traffic made it cost-prohibitive to install GSM-R for these areas and so a new radio system, with new base station and on-train equipment, was developed. This allows RETB to continue to operate on Band III Sub Band 1. RETB NG. References Vanns, Michael A (1997): An Illustrated History of Signalling. Ian Allan Publishing, Shepperton, England. External links Modernisation of the Cambrian Lines; includes discussion on a practical application of RETB. Comms Design Ltd - System developer for RETB Next Generation Railway signalling block systems