Proper traffic control is critical in highway work zone safety. Traffic control devices such as signs, barricades, cones, and plastic safety barrels are often used. Accidents can occur because of improper work zone design, improper work zone housekeeping, and driver negligence. One solution is to automate safety devices. This paper presents a mobile safety barrel robot. The Robotic Safety Barrels are the first elements of a team of Robotic Safety Markers (RSM) that includes signs, cones, and possibly barricades and arrestors. To be practical the system must be reliable and have a low per robot cost. A robot that malfunctions could enter traffic and create a significant hazard. Also, multiple safety markers are used and barrels are often struck by vehicles. Safety markers with a high replacement cost are not practical. This paper describes the motivation for the robotic safety marker system and how it could improve work zone safety. The design of three robot prototypes is presented. A control architecture is discussed that has been implemented in simulation and partially tested on the prototype robots.