Question Topic: Road and traffic signs
Explanation: These signals are found at level crossings, swing or lifting bridges, some airfields and emergency access sites. The flashing red lights mean stop whether or not the way seems to be clear.
Category: Road and traffic signs
References: The Official DVSA Guide to Driving: Section 6, Highway Code: Page 102, Know Your Traffic Signs: Page 13, Know Your Traffic Signs: Page 26, Know Your Traffic Signs: Page 120