A young boy's body is found in the luggage locker of a Trans Bridge Lines three axle airport transfer coach. The detectives visit the depot where several more of these beasts are seen. Three fleet numbers can be seen - 305, 309 and 314 (thanks Ian Hardie)
Episode 4.19: Appearances
"A group of school children board a transit bus in a blue and white livery. One of the children finds a suitcase under a seat. The bus is evacuated and the bomb squad X-ray the suitcase only to find a murdered child's body. The only time any id is visible is fleet number 1576. Both interior and exterior shots of the vehicle." (thanks Ian Hardie)