The National Highway Transportation Safety Administration has taken on this puzzle in a recent study.
The hypothesis was that the electric engines of hybrids made them less audible to bicyclists who otherwise can hear cars and trucks when they can't see them.
The overall circumstances of motor vehicle-bicycle crashes are common betwen hybrid and regular internal combustion (gasoline) cars. Most car or truck to bicycle crashes occur during daylight hours at low speeds.
Interestingly, a significant variable was for backing and parking cars. With standard gasoline vehicles, such collsions were far less likely. The notion is that two factors contributed to the hybrid car parking collisions. The first is that the low power for parking involves the use of the electric motor in hybrids which is virtually noiseless. The second factor is that both drivers and bicyclists may let their guard down in low speed parking situations.
Also, intersectional collisions between hybrids and bicycles occur more frequently again because initial acceleration at intersections is electric for hybrids. On the open road the numbers are the same for both gas and hybrid cars and the NHTSA is planning on a more comprehensive future study to arrive at proposed solutions.
For more see the following link : http://www-nrd.nhtsa.dot.gov/Pubs/811204.PDF