Hello, and welcome to OpenStreetMap. OpenStreetMap is a project for recording the world as it currently exists "on the ground", and should not be used to map historic features that have been removed (https://wiki.openstreetmap.org/wiki/Good_practice#Don't_map_historic_events_and_historic_features ). Because the Portsmouth Electric Railway was discontinued and removed in 1925, there is no longer any physical evidence of the route and it does not belong in OpenStreetMap. Historical features belong in OpenHistoricalMap (https://www.openhistoricalmap.org/ ) where they can be handled appropriately.

https://www.openstreetmap.org/changeset/148828827