1856), Didcot to (February 1872), Swindon to Thingley Junction, (June 1874), Thingley Junction to (March 1875), Bathampton to Bristol (June 1874), Bristol station area (May 1854). The broad gauge remained in use until 1892, at which point the last 500 miles of track were converted to standard gauge.

Between 1877 and 1899, the original dual tracks were widened to four in numerous places, mainly in the east half of the line: Paddington to (October 1877), Southall to (November 1878), West Drayton to (June 1879), Slough to east side