Heavy fog presents a significant safety hazard to drivers by reducing their ability to see the roadway and other vehicles. Even so, drivers often fail to adjust their speed to account for the reduced visibility, resulting in stopping distances that exceed visibility distance. Active delineators, or in-pavement light emitting diode (LED) markers, are an emerging technology which can be used to assist drivers in traveling through fog-prone areas by marking road or lane boundaries. However, there is a lack of research indicating how the presence of active delineators might also affect a driver’s behavior. This study sought to examine how the presence of active delineators in fog might affect drivers’ speed. Three lighting patterns and two brightness levels were tested. In daytime conditions, the delineators had no effect on speed. During nighttime conditions, participants often drove faster when the active delineators were present. Participants felt that the active delineators were helpful for navigating through the fog in both daytime and nighttime conditions, but preferred the higher brightness settings in the daytime.