RETBRadio Electronic Token Block (radio-based signaling system for use on single line railways)
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The next generation RETB system will be implemented on the rural single track lines from Glasgow to Oban via Fort William and from Inverness to the North Coast of Scotland at Thurso.
Installing ERTMS has cost pounds 60m and replaces RETB, an older, radio-based system, on the line and allows more trains to run.
Signals along one short section of the track not currently RETB controlled will be removed and the entire 136-mile route will be controlled from one site.