Hybrid cars might arguably be better for the environment, but according to the Japanese Transport Ministry, they could be dangerous to some pedestrians, as a result of their near-silence at low speeds. As a result, hybrid vehicles might be required to come equipped with a noise-making device.
The concern is that when operating on battery power it is difficult to hear a hybrid vehicle coming, which could make it a risk for the visually impaired. According to the Transport Ministry is "received opinions from automobile users and vision-impaired people that they feel hybrid vehicles are dangerous."
In response to those concerns, the Transport Ministry gathered a panel of "scholars, vision-impaired groups, consumers, police and the automobile industry to discuss the issue." Their conclusion? "To consider introducing a sound-making function" in hybrid vehicles. Profound!
Far be it from me to point out that even though the engine noise of hybrid vehicles is - generally - greatly lessened they do still produce tyre noise when moving and, perhaps more notably, are generally moving within other traffic. One quiet car amount hundreds of loud ones hardly poses a threat. Not to say that there are probably some occasions where a silent vehicle could be an issue; I just can't think of any.
Whether export-vehicles would be affected should regulations require hybrid vehicle manufacturers in Japan to add sound-emitters to their vehicles is, unsurprisingly, unclear. It's an interesting possibility to bear in mind, though - I'll take a quacking Prius, please.