What does this sign with a flashing yellow signal indicate?

• The drawbridge ahead is in operation; drivers must slow down and prepare to stop.
  Explanation:

  "When the yellow light on a drawbridge is flashing, it indicates that the drawbridge is in operation and may soon open to allow boats or ships to pass. Drivers must slow down and prepare to stop."
• The drawbridge ahead is not working; drivers must not proceed further.
• The drawbridge ahead will begin to operate; drivers must speed up and cross the bridge.
• The drawbridge ahead is in position; drivers may proceed.