Possible Clues:

• Extensive traffic jam
• Dense, motionless traffic
• Possible result of an accident
• Severe traffic congestion
• I'd look after the last king (Commonwealth's first king): I can't get out of it
• Traffic snarl-up
• Grating on part of canal system causing lack of flow
• Awkward rig left in wharf producing standstill
• Traffic congestion
• No movement when solving's impeded?