Possible Clues:

• Loafer that's not suitable for express train?
• Small blue train, one lagging behind
• Owls, bizarrely, train tortoise or snail?
• Small blue vehicle, one lagging behind
• Laggard finally leaves blue train
• One teaching a pig, possibly, to catch large snail
• Put brakes on bus for dawdler
• One unlikely to win a race with dimwitted trainer
• Plodder is to look into innovative cash cow
• Small blue vehicle certainly not one of the fleet