Car Choices, Affordability and the Environment


  1. Introduction and General Issues
  2. Efficiency of a Vehicle
  3. The Impact of the Weight of the Vehicle
  4. The Impact of Speeding and Brisk Driving

1. Introduction and General Issues

Daily transportation has become a problem in many respects such as for the environmental impact, congested traffic, and affordability for people who have to drive kilometres/miles to go to work or for shopping.

As far as global warming is concerned, according to the International Transport Forum at the OECD, road transports accounts for about 10.7 percent of all greenhouse gases emissions.

It should be noted that energy can take several forms, such as heat, light, motion, atomic or chemical energy. There are ways to change energy from one form to another, but those conversions always lead to a loss of usable energy through dissipation. There are intrinsic limits to the efficiency of energy conversion. The first landmark theoretical result about intrinsic limitations to the efficiency of energy conversion processes is the Carnot's Theorem for efficiency of a heat engine. There are additional causes for energy waste in real cases (due to irreversibility).

Note that the notion that car propelled by other means than a combustion engine (e.g. regular gasoline fuels), such as Battery Electric Vehicles, have less impact on the environment, and in particular on global warming is blatantly false and short sighted, as filling a battery requires a source of energy, and the corresponding supply of energy will have an impact on the global energy supply chains, and therefore on global warming and nuclear waste.

Some standardized test have been conducted so the car manufacturers would have to display the greenhouse gases emissions for the use of their cars. As was revealed through the Volkswagen emissions scandal, the whole industry (as other affair were later discovered with other big players of the automotive industry) was taking conscious steps to cheat on those test. This shows that we should pay little attention (if any) to the claims about the environmental of cars made by the industry.

2. Efficiency of a Vehicle

The energy consumed to propel a vehicle depends on three kinds of energy spending:

  1. The mechanical energy required to accelerate the vehicle and make it move, and also to make it climb slopes
  2. The lack of efficiency of the vehicle which produces a waste of energy, either through friction/dissipation, through imperfect conversion of energy form. That includes air friction.
  3. The efficiency of the different processes to produce the energy source on board the vehicle (be it refined gasoline, biofuel, electric battery load)

When assessing the global impact on resources or the environment of car use, the (fixed) costs of production of the vehicle itself (mining for materials, transformation for raw materials, transportation and assembly for the parts, etc.), including the batteries, also accounting for recycling and waste throughout the lifecycle of the vehicle must be taken into account. It should be noted that car batteries contain chemical which can have safety and pollution impacts, as well as resource drain, which should lead us to a reasoned use of battery electric vehicles, just as well as combustion engine vehicles.

3. The Impact of the Weight of the Vehicle

It should be noted that one of the most, if not the most, important criterion for both the environmental impact and for affordability of a car is its weight. Indeed,

  • The mechanical energy required to accelerate the vehicle and make it move, and also to make it climb slopes are directly proportional to the weight
  • The dissipated energy and friction energy, for a given kind of technology (say, a gasoline combustion engine which is currently the most affordable) does not depend much on the choice of car or manufacturer, and when it does, the the weight is also an important factor. At last, air friction is generally optimized to similar levels for cars in a similar weight range, and this drag is correlated to the size of the car, and therefore to its weight.
  • The fixed costs and impact to produce the car, as well as the waste throughout its lifecycle is also directly related to its weight.

So, if you really care about the environment, or if you find it hard to afford the fuel you need to go about your daily business, first thing:

Choose the lightest car!!!

4. The Impact of Speeding and Brisk Driving

The mechanical energy required to accelerate the vehicle and make it move, is related to the total variation of the speed (especially if the car is not designed to exploit the energy released by braking). Therefore, brisk driving through which you constantly accelerate only to brake the next instant leads to greater fuel costs.

The energy wasted due to air friction is highly correlated to the vehicle's speed, which leads to more efficient driving at moderate speeds.