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Directional sound can be used to provide warnings to specific vehicles without disturbing other vehicles on the highway. An example of such an application is the need to alert a vehicle that is likely to intrude into a highway construction work zone. Long-distance auditory warnings potentially reduce the time for the driver to visually locate the work zone. This paper reviews the currently available 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 found to be effective at generating highly directional sound. However, when issues of cost, installation, maintenance, and price are considered, the more suitable technology for work zones is found to be arrays of flat-panel loudspeakers with time delay control. Such a system is inexpensive and can be used to effectively generate directional sound for long-distance auditory warnings. This paper shows that an annular pattern of flat-panel speakers can provide directional sound along a highway lane, with no real-time control of time delay necessary. Hence, an extremely inexpensive and portable system can be obtained, with components consisting of compact flat-panel speakers, a battery, power supply, and inexpensive electronics. In terms of performance, the developed system can provide a difference in the sound level of 6 dB or higher between adjacent lanes at all frequencies in the range of 2-4 kHz at distances of up to 40 m from the location of the warning system.