What does the drawbridge 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 is flashing, the drawbridge is in operation. Drivers must break their speed and prepare to stop."
• The drawbridge ahead is not working; drivers must not proceed further.
• The drawbridge ahead begins to operate; drivers must speed up and cross the bridge.
• The drawbridge ahead is in position; it is safe to proceed.