What does this sign mean?

Explanation: This is the sign for a clearway. Clearways are stretches of road where you aren't allowed to stop unless it's an emergency. Stopping where these restrictions apply may be dangerous and is likely to cause an obstruction. Restrictions might apply for several miles and this may be indicated on the sign.

Category: Road and traffic signs

References: The Official DVSA Guide to Driving: Section 6, Highway Code: Page 107, Know Your Traffic Signs: Page 55