Use of truck-mounted changeable message signs (TMCMSs) during mobile maintenance operations is desirable to provide drivers with information to better prepare them for unexpected conditions. Traditionally, temporary traffic control devices used during mobile operations have been limited to arrow boards and sometimes static warning messages mounted on a work vehicle. The use of warning signs in advance of an operation typically is not practical because of the constant movement and stop-and-go nature of the work. TMCMSs can fill an information gap for these mobile operations and provide drivers with better information about them, including actions to be expected. This paper describes the use of findings from a human factors laboratory study and basic message design principles to create a sampling of recommended messages for use on TMCMSs during mobile maintenance operations. These messages were defined by the type of work, road type, and the identified concerns to be addressed.