Engineering inevitably involves compromises.  At the current stage of battery technology, batteries are still heavy pieces of equipment.  With a hefty battery, the typical hybrid vehicle, although remarkably fuel efficient, is about 10% heavier than it would be if the power source was solely a conventional fossil fuel engine.  In the smaller and mid-size vehicles, the weight of the hybrid version of a particular model is 300 to 400 pounds more than the comparable conventionally powered vehicle.

We might expect that extra weight is a negative.  However, it gives the hybrid vehicle one engineering advantage that was recognized long before the hybrid concept was even dreamt of.  It is a well-established principle of physics that, in a crash involving two vehicles, the heavier vehicle will have the advantage in survivability, and the lighter vehicle will suffer the most damage.

Why so?  The heavier vehicle just keeps going and the lighter vehicle yields.  The occupants of the heavier vehicles are subjected to less deceleration stress than the occupants of the lighter vehicle, as the heavier vehicle makes a cushion out of the lighter vehicle.

In single vehicle accidents a heavier vehicle may also be safer than its lighter counterpart, as the heavier vehicle will be more likely to plough through obstacles and take longer to come to a stop than a lighter vehicle that will more readily come to a bone jarring halt.

Given the safety cage design of passenger compartments of current vehicles, plus seatbelts and airbags, occupants of today’s vehicle enjoy unprecedented protection.  The big threat of physical harm is no longer intrusions or disintegration of the vehicle, but violent deceleration.

The American “Highway Loss Data Institute” (HLDI) has recently presented a study which looks at the forgoing assumptions and provides a statistical analysis of a collection of crash results involving of hybrid versus comparable conventional models.  How much safer are you, when riding in a hybrid?  25% says the study.

The HLDI study also points out another issue that nobody saw coming.  You cannot hear the approach of a hybrid vehicle running on battery mode.  They just “glide along.”  This is a big problem for pedestrians.  The old adage of “stop, look and listen, before you cross the street” provides incomplete guidance in dealing with the presence of a stealthy hybrid vehicle.

Hybrid vehicles are now reported to be causing 20% more injuries to pedestrians than conventional vehicles.  The problem is so bad that the United States Government has given the National Highway Traffic Safety Administration three years to come up with proposed legislation that would mandate some sort of hybrid vehicle warning system installed in the vehicle, to alert pedestrians.

What form this alert system will take is difficult to imagine.  We certainly do not need more noise pollution, in the form of a “hybrid in the neighborhood” noise.  It is likely that increasingly sophisticated sensors on the vehicle – essentially a form of pedestrian radar and infra-red detection – will come to market soon, and limit the problem.  When a pedestrian “threat” is detected, at that point an audible sound or warning will be emitted from the hybrid vehicle.