“We have a friend called Bertie, and he's a bus, but he likes the railway. Sometimes he teases us about it, but he'd never want to see it ripped up.”
― Duck telling Bulgy about Bertie

Bertie is a little red bus who works alongside Thomas' Branch Line.

As in the television series, Bertie reprised some of his roles from the Railway Series but was later chosen to take visitors to the Vicar's party and teased Trevor by calling him a "stickinthemud" and old fashioned. However, he proceeded to get himself stuck in the mud and had to be pulled out by Terence. After that, Bertie thanked Trevor and gave him an apology for teasing him.

When Edward had an accident on the day before he was to take the Brass Band to a concert, Bertie had to take them instead but got stuck in the mud again. Luckily, Edward was repaired and took the Brass Band to their concert.

Bertie is continuously alluding to his race with Thomas and how he could win next time. He actually raced Thomas again and won after Thomas got sidetracked with collecting the sports medals.

Bertie and Thomas have seemed to continue this tradition of racing. However, in the seventeenth series, he was rerouted, giving him an advantage. Thomas is still able to beat him occasionally.

In the nineteenth series, he, Thomas and Spencer got into an argument after Mr. Percival claimed two wheels was best; Bertie argued four wheels was in fact best. He tried to prove his point by taking The Duke and Duchess of Boxford to Callan Castle after both Thomas and Spencer failed to do so, but he too failed after receiving a flat tyre. Harold eventually came to the Duke and Duchess' rescue. Bertie later teased Thomas by telling him about what was on the other side of a mountain on his branch line. Thomas was cross by Bertie's teasing and became determined to find out what was there. Thomas eventually discovered it was a roadside billboard Bertie was describing, though he got into an accident while trying to find out. Bertie visited him at the Steamworks and apologised, though Thomas was able to trick him into believing that he was getting fitted with wings.

In Sodor's Legend of the Lost Treasure, while he and Thomas were racing, Thomas nearly collided with Toby while Bertie nearly collided with Oliver the Excavator. At Ffarquhar, he complained that he was always getting stuck behind slow construction vehicles since the construction of the new branch line had started. He was then seen on the road by the Harwick Branch Line. Sheep were in his way, but Bertie just smiled.

In the twentyfirst series, Bertie ended up breaking down while he and Thomas were racing. This ended up with Thomas taking on his passengers but ended up getting requests for lots of unscheduled stops, which made him run late. However, Bertie was soon temporarily replaced by Bulgy, leading to Thomas running on time.

After being repaired, he shared the mantle of keeping Bulgy in line. Bulgy, however, was still up to his old ways, so Bertie had to remind him that the Fat Controller brought him back to help him with the passenger service; he later broke down due to struggling with passenger transport (flourished due to train halting courtesy of Bulgy). Bulgy took his passengers while Butch towed him away.

Later, when Percy created rumours of a railway show for little engines at Ulfstead Castle, Bertie took Thomas' passengers from Ffarquhar to Knapford after Thomas abandoned his duties to attend.