Directional sound can be used as a warning signal to denote that failure to follow an indicated action could result in serious accidents. In some applications such as to alert a vehicle that is likely to intrude into a highway construction work zone, long distance auditory warnings are necessary. In such cases, directed sound could be utilized to warn the specific vehicle without disturbing other vehicles on the highway. This report reviews the currently available scientific technologies that can potentially be used to develop a long distance auditory warning system for highway work zone applications. Of these, ultrasound based parameter arrays and time delay controlled arrays of compact ordinary speakers are taken up for detailed analysis and experimental evaluation. An ultrasound based parametric array is the most appropriate technology for generating highly directional sound. However, if cost, installation, maintenance, and price are considered, the most suitable technology is found to be arrays of flat panel loudspeakers with time delay control. Such a system can be used to generate directional sound effectively for long distance auditory warnings.