Westbury signalbox, so called 'The Cathedral' because of its large, cavernous interior, controls part of the Berks and Hants line around the Westbury area. It fringes with Reading panel to the east, Swindon panel on the Melksham branch, Bristol panel on the Trowbridge line, Salisbury panel to the south, Yeovil signalbox on the Weymouth line, and Exeter panel to the west.
The large yard areas at Westbury sees a lot of activity, both freight throughout the day and empty passenger stock in and out at the start and end of the day. Stone trains originate from the quarries at Merehead and Whatley, both of which are included.
Although not controlled by Westbury, the Berks and Hants panel of Reading signalbox has also been included. This gives a continuous line of control from Aldermaston to Somerton, a total of 100 continuous route miles. Added to that the other branches and you have over 140 route miles!