On 24 July 1940, the line through Porirua, from Wellington to Paekakariki, was electrified and double track completed from Plimmerton to South Junction, just north of Muri railway station. Electrification allowed the introduction of electric ED class locomotives, first introduced in 1938 for use on this line, to haul passenger and goods trains. Electric locomotives eliminated the smoke nuisance in the tunnels on the line and allowed longer trains to run. DM/D electric multiple units first ran to Porirua on 5 September 1949 and replaced the majority of locomotive-hauled passenger trains and allowed a more frequent and faster train service. The duplication of the line from Plimmerton to South Junction allowed a more frequent train service between Porirua and Paekakariki