**8. Larger automobiles**

There is much potential of reducing energy consumption in automobiles, by moving to smaller and more efficient automobiles. A recent StatsCan report indicated that Canadians spend 18 % of disposable income on transportation. The fundamental issue is that automobiles do not need to be as large with low gas mileage, as they are today. The present popularity of larger cars and SUVs are unsustainable, over the next few decades. Studies have shown that the popularity of larger automobiles and SUVs is largely due their perceived and real safety in case of a collision. This popularity is in addition to other factors, such as comfort and space, and the status they convey about the owners.

During an impact, the impulse on passengers of a heavier automobile is less than the impact on a lighter car. We consider an automobile of mass M1 travelling at velocity VI hitting a stationary automobile of mass M2. We assume they move away with a common velocity VF. From the law of conservation of momentum, their final velocity will be

$$\mathbf{V\_{F}} = \frac{\mathbf{M\_{1}V\_{1}}}{\mathbf{M\_{1} + M\_{2}}}$$

The impulse on passengers in the first car is

$$\mathbf{M}\_1[\mathbf{V}\_1 \cdot \frac{\mathbf{M}\_1 \mathbf{V}\_1}{\mathbf{M}\_1 + \mathbf{M}\_2}]$$

The impulse on passengers in the second car is

$$\mathbf{M\_2} \,\,\frac{\mathbf{M\_1}\mathbf{V\_l}}{\mathbf{M\_1} + \mathbf{M\_2}}.$$

Analysis of the above shows the smaller impact forces on the passengers of the larger car, and consequently greater safety.

This safety during collision, and the status conveyed by larger automobiles, has at least contributed to a "size race" among consumers in pursuit of larger cars. There is much scope of reducing this "size race" among consumers, greatly favoring fossil fuel conservation.

#### **8.1 Sports utility vehicles**

The Sports Utility Vehicle (SUV) has been popular for at least 2 decades. Today, the largest SUV weighs as much as two mid-size SUVs and gets just 13 mpg on the highway. While there have great research and incentives on decreasing the size of cars, the SUV had initially exploited a legal loophole by being built on the chasis of trucks, bypassing the fuel efficiency required of cars. Consumers, eager for increased safety, had contributed to the great popularity of SUVs, owing to their increased safety arising from greater weight.

Numerous federally sponsored studies (speakout.com), show that car occupants are more likely to be killed when struck with by a SUV than by another car. Many SUV drivers have said they buy the big vehicles because they make them "feel safe."

These SUVs and large cars alongside more efficient cars today, are examples that there is great scope of improving energy conservation by implementing policies to discourage this "size race" by consumers in their pursuit of safety in collisions.
