levels of traffic saw the line through Sea Mills doubled in the early 1900s, and the opportunity was taken to rebuild the station. A second platform opened on 6 January 1907 to the west of the tracks to serve northbound trains. The original platform now exclusively served southbound trains, and was lengthened to , the same length as the new platform. A station building was constructed on the original platform in a domestic style, with an arched terracotta entrance, spar-covered walls and a high-pitched tiled roof. The building contained a booking hall, booking office, toilets and a ladies' waiting room. A smaller building on the northbound platform contained a general waiting room. The subway under the bridge over the River Trym was also built at this time, with the porter's job being expanded to include washing the rubbish out of the subway after high tide, for which the railway provided a hosepipe and Wellington boots. By 1910 there were 17 trains from Bristol to Avonmouth and 15 back, increasing to 21 and 19 respectively by 1920, though not all stopped at Sea Mills. The station was completely closed on Sundays. After the First World War, construction of the Bristol Portway along the Avon Gorge necessitated the closure of the line from Sneyd Park Junction to Hotwells, with trains along it ceasing on 3 July 1922. By this point there were nine trains per day from Hotwells, and eight return. To compensate for the loss of service, the Great Western provided an additional four trains daily towards Bristol and six toward Avonmouth. In 1923, grouping resulted in the Midland Railway being absorbed into the London, Midland and Scottish Railway (LMS), and the line continued in a joint arrangement between the Great Western and the LMS. From 1928 many trains to Avonmouth were extended to . By 1947, just before the railways were nationalised, there were 33 services each direction between Avonmouth and Temple Meads, with 18 on Sundays. Some trains made circular trips to and from Temple Meads via Clifton Down and or . When the railways were nationalised in 1948, services at Sea Mills came under the aegis of the Western Region of British Railways. Staffing by this point had increased to two porters and two lad porters, managed by the stationmaster at . By 1961 this was reduced to two porters, then to one in 1965. Service levels had