The Troublesome Trucks are Bio-Fused rolling stock.
When the government shut down Bio-Fusion operations on Sodor there were several people in the middle of their operation, the scientists had complete their procedures quickly as they would die. As a result the remaining people were turned into Troublesome Trucks as the design was simple. However, the trucks rarely had the brain capacity to produce long term memory. Their vital organs were left out in the open, which increases the risk of infection, causing them to die a slow and painful death.