Effects of Auditory Display Types and Acoustic Variables on Subjective Driver Assessment in a Rail Crossing Context

Highway-rail grade crossings (HRGCs) present multiple collision risks for motorists, suggesting the need for additional countermeasures to increase driver compliance. The use of in-vehicle auditory alerts (IVAAs) at HRGCs has been increasing, but there are limited standards or guidelines on how such alerts should be implemented. In the current study, we sought to investigate the effect of different auditory display variables, such as display type and acoustics, on subjective user assessments. We recruited 24 participants and asked them to rate 36 different IVAAs belonging to one of three display types (earcons—short synthetic tones, speech alerts, and hybrid alerts consisting of an earcon and speech) along 11 subjective ratings. Results showed that a hybrid alert led to better overall ratings for acceptance, safety, and semantic understanding when compared with earcon or speech alerts. Additional analyses revealed that semantic variables, such as speech order and gender, should be accounted for when designing IVAAs in an HRGC context. Hybrid IVAAs with spatial audio showed lower Urgency and Hazard level ratings. Findings of the current study can help inform the design of IVAAs for HRGCs.

Multiple-Collision Free-Electron Laser Compton Backscattering for a High-Yield Gamma-Ray Source

We observed multiple-collision free-electron laser (FEL)-Compton backscattering in which a multi-bunch electron beam makes head-on collisions with multi-pulse FELs in an optical cavity, using an infrared FEL system in the storage ring NIJI-IV. It was demonstrated that the measured spectrum of the multiple-collision FEL-Compton backscattering gamma rays was the summation of the spectra of the gamma rays generated at each collision point. Moreover, it was demonstrated that the spatial distribution of the multiple-collision FEL-Compton backscattering gamma rays was the summation of those of the gamma rays generated at each collision point. Our experimental results proved quantitatively that the multiple collisions in the FEL-Compton backscattering process are effective in increasing the yield of the gamma rays. By applying the multiple-collision FEL-Compton backscattering to high-repetition FEL devices such as energy recovery linac FELs, an unprecedented high-yield gamma-ray source with quasi-monochromaticity and wavelength tunability will be realized.