What action does a single alternately flashing red signal require drivers to take?

• Proceed with caution.
• Come to a complete stop and proceed when safe.
  Explanation:

  "A single alternately flashing red signal requires drivers to stop completely and proceed only when it is safe. This signal is often used at railroad crossings or intersections where drivers must come to a full stop and ensure the way is clear before continuing."
• Increase speed to clear the intersection quickly.
• Ignore it as the signal is out of order.