Heritage award for historic rail line.
Talyllyn, which was built in 1866 to carry slate and passengers in mid Wales, became the world's first volunteer-run heritage railway in 1951.
The cartoon engine's creator, the Reverend W Awdry, joined the volunteers in 1952.
The railway is the 67th Engineering Heritage Award winner. Others include the world's first railway locomotive.
The 7.25 mile (11km) railway in Tywyn, Gwynedd, nearly closed when the line's owner died in 1950 and was saved by a newspaper advert by rail enthusiast Tom Rolt, in the Birmingham Post.
The Talyllyn Railway Preservation Society (TRPS) was formed as a result of a flood of responses to that advert, and in May 1951 it became managed and run entirely by volunteers.
"Sixty years ago volunteers decided to save this particular railway and since then all our heritage railways have started from there," said Prof Isabel Pollock, of the Institution of Mechanical Engineering.
"Think how many we have [now], how many engines have been saved from being chopped up, to create the leisure business that we have in heritage railways."
The Rev Awdry, who was born 100 years ago, began writing Thomas the Tank Engine stories in 1945.