Rear-end crashes involving heavy trucks occur with sufficient frequency that they are a cause of concern within regulatory agencies. In 2006, there were approximately 23,500 rear-end crashes involving heavy trucks which resulted in 135 fatalities. As part of the Federal Motor Carrier Safety Administration's (FMCSA) goal of reducing the overall number of truck crashes, the Enhanced Rear Signaling (ERS) for Heavy Trucks project was developed to investigate methods to reduce or mitigate those crashes where a heavy truck has been struck from behind by another vehicle. Researchers also utilized what had been learned in the rear-end crash avoidance work with light vehicles that was conducted by the National Highway Traffic Safety Administration (NHTSA) with Virginia Tech Transportation Institute (VTTI) serving as the prime research organization. ERS crash countermeasures investigated included passive conspicuity markings, visual signals, and auditory signals. In regards to auditory signal development, the focus of this paper, the feasibility of generating an exterior narrow beam-width auditory signal was investigated; however, the two proposed concepts (i.e., tube design and parabolic reflector) were unable to achieve the goal of ±5 degrees (deg). Because this narrow beam-width could not be obtained, further use of either concept may needlessly distract other drivers in adjacent lanes. Vehicle-to-vehicle communications (V2V) has the clear benefit over an exterior auditory signal in that more control of the signal's sound, directionality, and amplitude can be maintained inside the following vehicle. It was recommended that further ERS testing not include the auditory signal component of the research project and that efforts be focused on visual crash countermeasures.