Road safety is no laughing matter for the Federal Highway Administration, which warned against humor and pop culture references in an updated manual of traffic sign standards.

The 11th edition of the Manual on Uniform Traffic Control Devices for Streets and Highways was released in December and became effective Thursday, according to the Federal Register. It had last been updated in 2009.

The manual is the national standard for traffic signs, including changeable messaging on roadways by state and local agencies.

State agencies have two years to implement the mandated standards.

In the manual, the FHWA slapped examples such as “Hocus pocus, drive with focus,” used in New Jersey, and “Visiting in-laws? Slow down, get there late,” used in Ohio, according to The Associated Press.

The signs shouldn’t “be used to display a traffic safety campaign message if doing so could adversely affect respect for the sign. Messages with obscure or secondary meanings, such as those with popular culture references, unconventional sign legend syntax or that are intended to be humorous, should not be used, as they might be misunderstood,” the FHWA wrote.

It said some references have confused motorists, such as signage in Ohio highlighting the 1983 movie “A Christmas Story.”

“Life is fragile, and we spelled it out ‘fra-gee-lay.’ And we thought, man, everybody’s seen ‘A Christmas Story,’ especially in Ohio. Everyone will get that. There are a lot of people who didn’t. … We got some confused phone calls and emails and so we won’t use that one again,” Ohio Department of Transportation Press Secretary Matt Bruning told NPR.

Humor, some state officials contend, helps grab motorists’ attention.

“There’s only so many ways you can say, ‘Don’t text and drive.’ People tune you out,” Mississippi Department of Transportation spokesman Paul Katool told The New York Times.

In a release in the Federal Register, the FHWA noted the guidance isn’t a blanket ban on funny signage.

“The guidance provisions, as adopted, can be deviated from based on engineering judgment. However, FHWA believes these are important considerations as not to diminish respect for the sign,” the register reads.

• Brad Matthews can be reached at bmatthews@washingtontimes.com.