In 2023, when the State of Utah stopped using humorous messages on highways to encourage driver safety, a local newspaper wondered if disapproval from the Federal Highway Administration might have been a factor in the decision. It turns out that the state just felt a change would be helpful and found an alternative outlet for humor in the state department of transportation’s X account. News reports point to similar experiences in Arizona and New Jersey.

Where did these states get the idea that the federal government was trying to stop their road sign fun?

The answer is that the (1,161-page) 11th edition of the Manual on Uniform Traffic Control Devices for Streets and Highways, published by the U.S. Department of Transportation’s Federal Highway Administration, included new language:

A CMS [changeable message sign] should not 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 or understood only by a limited segment of road users and require greater time to process and understand.

After Arizona officials expressed concern with the new language, a spokesperson for the agency pointed out that the manual language was just “guidance,” not an explicit ban.

These stories illustrate a serious issue with constitutional and practical significance: the practice of federal agencies providing guidance to states and others whom the agencies regulate.

This report describes agency guidance and its legal and practical significance, including legal concerns about its use. It will then describe recent efforts by the national and state governments to respond to these concerns, particularly related to increasing the transparency of this guidance, before concluding with some recommendations.