Listed below is one of the many articles I found while researching this concern. It was found on NPR.com.
Nearly Silent Hybrid Cars May Endanger the Blind
Hybrid vehicles may pose a deadly threat to people who rely on their hearing to navigate streets and crosswalks. The National Federation of the Blind is calling for hybrid manufacturers to make their cars sound like traditional car engines, so that blind people can hear them coming.
Robert Siegel talks to Dr. Fredric Schroeder, first vice president of the National Federation of the Blind.
We confirmed the comparative noise levels of hybrid and gas-powered cars, using a Toyota Prius — one of the more popular models. Toyota officials say they are studying the issue; they also note that on the opposite side of the issue are advocates of reduced noise pollution.
The Toyota officials say that the quieter cars has led them to advise drivers and pedestrians to exercise increased caution.