It is a minimum gauge railway based on the Ravenglass and Eskdale Railway in Cumbria. In the stories, it was originally built to bring waste from the lead mines in the hills to Arlesburgh at the end of Duck's branch line, where it would be distributed to the other railways on Sodor for use as ballast. The line also carries tourists.
The railway's controller is Mr. Fergus Duncan, a dedicated man known as the Small Controller. This nickname is a joke, as he is a very tall man.
The Arlesdale Railway made its first appearance in the book Small Railway Engines, and was the main focus of the book Jock the New Engine. It has also made cameo appearances in Oliver the Western Engine, Duke the Lost Engine and Wilbert the Forest Engine.
It made its debut in the TV series in the 2015 Thomas & Friends special Sodor's Legend of the Lost Treasure and later appeared in Season 20.
The 15-inch gauge railway runs from Arlesburgh West (aka, Arlesburgh Junction); where it meets Duck's branch line to the village of Arlesdale, stopping at Arlesburgh Bridge Street, Ffarquhar Road, Marthwaite and Arlesdale Green en-route, along the way.
The line follows part of the route of the old (and historic) Mid Sodor Railway (Generally known as Duke's old line). At Arlesdale Green it leaves this route and takes a new, southerly course to Arlesdale.
All of the locomotives on the Arlesdale Railway are based on real locomotives at the Ravenglass and Eskdale Railway. The three original engines of the Arlesdale Railway – Rex, Bert and Mike – were brought to Sodor from an unspecified railway in England which closed in 1967. Each is identified by nameplates mounted each side of its smokebox (in the case of Frank, its hood and Jock, its boiler) and 'Arlesdale' written on its tender sides.
Rex is a green engine on the Arlesdale Railway who enjoys nothing more than teasing Mike. He is a hard worker, but sometimes has problems with traction.
After his old line in England closed down in 1967, he, Mike and Bert were bought by Sir Topham Hatt and the consortium that owned the Arlesdale Railway. He and his two companions were placed on mining and tourist traffic. After the railway secured a deal to transport wool to Arlesburgh, Rex was chosen to pull the first train, but after a negligent farmer spilt some wool bales on the rails he was derailed. His train was rescued, but Rex had to remain there until the end of the same day until being lifted out.
Rex is based on the Ravenglass and Eskdale Railway's "River Esk", built in 1923 in Colchester by Davey, Paxman and Co.
- Tom Stourton (UK/US; Sodor's Legend of the Lost Treasure onwards)
- Yuta Odagaki (Japan; Sodor's Legend of the Lost Treasure onwards)
Bert is smaller but older than Mike and Rex, and is the quietest of the first three Small Railway engines. For a long time he had trouble with steaming, but he has been rebuilt with a taller chimney and cab which mean that he no longer suffers from shortness of breath. This modification has not appeared in the book illustrations, but is mentioned in "The Island of Sodor: Its People, History and Railways".
- Keith Wickham (UK/US; Sodor's Legend of the Lost Treasure onwards)
- Mitsuhiro Sakamaki (Japan; Sodor's Legend of the Lost Treasure onwards)
Mike is a strong engine who prefers goods trains to passengers. His temper matches his paint, as he can often be hot-headed. He is proud of his shrill whistle, which he once lost trying to shoo a cow. He arrived at the station along with Rex and Bert in 1967 after their line in England was closed down.
Mike is based on the Ravenglass and Eskdale Railway's "River Mite", owned by the R&ERPS and built in 1966 by Clarkson's. He is painted red with blue stripes.
- Tim Whitnall (UK/US; Sodor's Legend of the Lost Treasure onwards)
- Tomohiro Tsuboi (Japan; Sodor's Legend of the Lost Treasure onwards)
Frank is a diesel with a tendency to be grumpy. He sometimes loses his temper, which once caused him to crash into the back wall of the shed. Despite this, he is a hard worker and is sometimes called upon to rescue engines who have broken down.
Frank is based on the Ravenglass and Eskdale Railway's "Perkins", which was constructed in 1984 at Ravenglass, a rebuild of a 1929 Muir-Hill tractor. He is light grey with a red stripe.
Jock is the newest steam engine on the Arlesdale Railway, and also the strongest. He was almost entirely built at the Arlesdale Railway's works. He was first mentioned in "The Island of Sodor: Its People, History and Railways", but made his first proper appearance in the eponymous book "Jock the New Engine". Jock was very cocky when he was first built, but soon learned the value of teamwork. His name comes from the fact that he is painted to resemble the locomotives of the Highland Railway in Scotland – a yellow-green colour with red lining. The name was suggested by Douglas, who remembered the Highland Railway from his youth.
Jock is based on the Ravenglass and Eskdale Railway's Northern Rock, built at Ravenglass in 1976.
Blister I & Blister II
Blister I and Blister II are small twin diesels that were only mentioned in "The Island of Sodor: Its People, History and Railways". Not much is known about them, apart from the fact they have regular engine troubles and are particularly difficult to start - which is how they got their names. This is based on the trouble experienced with the Muir-Hill Fordson granite tractors that worked at Ravenglass with stone traffic until 1953.
Both are painted black with black and yellow stripes around their faces. Both are based on the Ravenglass and Eskdale Railway's Lister diesel "Cyril".
Sigrid of Arlesdale
Sigrid of Arlesdale is a diesel locomotive working on the Arlesdale Railway. She has not appeared in the Railway Series, but she was mentioned in "The Island of Sodor: Its People, History and Railways". She is painted a two-tone blue livery, and is the only female locomotive character in the Railway Series who is not standard gauge.
She has also been seen on the Ravenglass and Eskdale Railway: her real-life counterpart, Shelagh of Eskdale, has been dressed-up with a face to represent her at Day out with Thomas events, whereas formerly they named her "BoCoBo", after the locomotive's wheel arrangement.
The railway has a number of passenger carriages for tourist traffic. The original coaches, which were a mixture of open (roofless) and "semi-open" (roofed, but doorless) types, were obtained from the same railway in England as the locomotives. The semi-open coaches have since been replaced with closed saloon carriages built at Arlesburgh Works. All the coaches are painted a deep pink colour.
For ballast traffic, the railway has a fleet of smooth-running bogie hopper wagons. These can be unloaded via a chute into waiting (standard gauge) trucks on the Fat Controller's Railway. The hopper wagons and unloading chute are based on similar designs once used on the Ravenglass & Eskdale Railway, who have provided much co-operation to the line.
In the television series the railway owns two kinds of wagons: the ballast hoppers and scaled down 7-plank open wagons for carrying wool. The railway also has several open-topped carriages.
- Railway engines (Thomas & Friends)
- Narrow gauge engines (Thomas & Friends)
- Rolling stock (Thomas & Friends)
- Non-rail vehicles (Thomas & Friends)
- North Western Railway
- Skarloey Railway
- Awdry, Rev. W., Small Railway Engines
- Awdry, Rev. W., Oliver the Western Engine (cameos)
- Awdry, Rev. W., Duke the Lost Engine
- Awdry, Christopher, Jock the New Engine
- Awdry, Christopher, Wilbert the Forest Engine (Rex, Mike and Jock do not speak)
- Awdry, Rev. W. and G., The Island of Sodor: Its People, History and Railways
- Awdry, Christopher, Sodor: Reading Between the Lines
- Clutterbuck, Martin, The Real Lives of Thomas the Tank Engine
- Sibley, Brian, The Thomas the Tank Engine Man