Dean Forest Railway says it wants to run three steam trains a day between Lydney and Parkend this summer. An extension of the current line - which only runs as far as Whitecroft - is due to be finished in June.
During the spring the line's operator will attempt to get the new line passed by the Railway Inspector.
The provisional timetable is for trains to leave Lydney at 1120, 1310 and 1505, with return journeys leaving at 1215, 1415 and 1600.
Dean Forest Railway is run by unpaid volunteers.
The organisation took over the branch line after British Rail stopped running services on it during the 1970s.