Once acquired, the data gathered using PULSE Time Data Recorder was subsequently post-processed using B&K PULSE Reflex software, along with Microsoft Excel. These software were used together to process and analyze the recorded data. The measurements collected confirmed that the presence of intervening vehicles do have a significant role in hindering the effectiveness of emergency vehicle sirens. From the manufacturer of the e-Q2B electronic siren, the frequency range is stated to be from 725 to 1600 Hz. (Federal Signal: Safety and Security Systems, 2012) This range will also be the focus of the analysis for this study. All distances reported will be measured from the siren speakers to the HATS device. For the majority of the data, the Fast Fourier Transform (FFT) analysis was used to examine the frequency spectral of the siren signals. The primary focus of this study was to analyze the off-axis, or perpendicular shadowing scenario. This form of shadowing would occur at an intersection, and is believed to be a factor in many emergency vehicle collisions. The first experiment had the vehicles positioned with their front bumpers in line with one another to simulate them being stopped at the same point in adjacent lanes at an intersection. The data concluded that at a receiver distance of 17.8 m from the siren speakers, the recorded SPL was significantly lower. At the majority of the frequencies of interest, the SPL is 5 dB higher when the shadow vehicle is absent. It is also important to note that there are multiple data points where the SPL is 10 dB higher for the case of no shadow vehicle present. This correlates to a perceived change in loudness of a factor of 2. A summary of the data is illustrated in Figure 3.