Rumble

Abstract: This synthesis will be of interest to traffic engineers, highway design engineers, highway maintenance personnel, those responsible for toll plaza design and operation, and others concerned with the operation, safety and design of the roadway environment. Information is presented on the various applications of rumble strips on the traveled way and on highway shoulders. This synthesis describes the state of the practice with respect to placement, operational and safety effects, design, installation, and cost and service life of rumble strips. This report of the Transportation Research Board also discusses the effectiveness of rumble strips in preventing or reducing accidents. It provides information on the potential adverse effects of rumble strips, such as noise, motorist use of opposing lanes to avoid rumble strips, maintenance problems, and concerns of special users such as senior citizens, bikers, and truckers. The need for signing and public information support are also discussed. The synthesis presents several recommendations for future research.

Abstract: Recent comparative data reveal that formant frequencies are cues to body size in animals, due to a close relationship between formant frequency spacing, vocal tract length and overall body size. Accordingly, intriguing morphological adaptations to elongate the vocal tract in order to lower formants occur in several species, with the size exaggeration hypothesis being proposed to justify most of these observations. While the elephant trunk is strongly implicated to account for the low formants of elephant rumbles, it is unknown whether elephants emit these vocalizations exclusively through the trunk, or whether the mouth is also involved in rumble production. In this study we used a sound visualization method (an acoustic camera) to record rumbles of five captive African elephants during spatial separation and subsequent bonding situations. Our results showed that the female elephants in our analysis produced two distinct types of rumble vocalizations based on vocal path differences: a nasally- and an orally-emitted rumble. Interestingly, nasal rumbles predominated during contact calling, whereas oral rumbles were mainly produced in bonding situations. In addition, nasal and oral rumbles varied considerably in their acoustic structure. In particular, the values of the first two formants reflected the estimated lengths of the vocal paths, corresponding to a vocal tract length of around 2 meters for nasal, and around 0.7 meters for oral rumbles. These results suggest that African elephants may be switching vocal paths to actively vary vocal tract length (with considerable variation in formants) according to context, and call for further research investigating the function of formant modulation in elephant vocalizations. Furthermore, by confirming the use of the elephant trunk in long distance rumble production, our findings provide an explanation for the extremely low formants in these calls, and may also indicate that formant lowering functions to increase call propagation distances in this species'.