Final answer:
The townspeople should be concerned because the sound intensity level would reach 100 dB, exceeding the recommended level of 85 dB. Health implications may arise from such sustained noise exposure. Destructive interference might offer a technique to reduces noise levels.
Step-by-step explanation:
The concern in the question pertains to the projected increase in sound intensity level due to the introduction of train service in a downtown area. With the current sound intensity level at 70 dB, and the mayor's assurance of a 30 dB difference, the resulting sound intensity level would be 100 dB. Given that health recommendations generally advise against exceeding 85 dB for 8-hour daily exposures without hearing protection, the citizens have cause for concern as this level of noise can be harmful long-term and could lead to hearing issues.
Additionally, the concept of destructive interference in sound is also relevant here, as it is a technique that can be used to reduce noise levels in various settings, for instance, in commercial aircrafts. Although complete destruction of sound is challenging, a significant reduction of noise levels is possible, suggesting that similar solutions could potentially be considered to address the community's concerns about the noise from the new train service.