By Ryan McGreal
Published August 12, 2005
North America, with about five percent of the world's people, accounts about a quarter of the world's oil consumption. Of that, more than half goes into transportation in what is arguably the most wasteful system imaginable.
It's no surprise that our surface transport network, such as it is, runs on oil: because of its density and portability (see Peak Oil, Part II of this series), oil is the ideal fuel for a distributed system of private vehicles. Each car can carry its own fuel source with it, and more fuel can be transported easily to a vast number of refueling stations located conveniently across the continent.
Because oil is so energy dense, cars can carry it around with them without its additional mass consuming much energy. If our fuel was much less energy dense, it would not be practical to build our transportation system the way we have done.
To explain why, let's take a compact car that weighs 1,200 kilograms and has a fuel efficiency of 15 kilometres per litre (km/l). Our car has a 40 litre gasoline tank, and 40 litres of gasoline weigh around 30 kilograms. Those 30 kilograms of gasoline can move our 1,200 kilogram car a distance of 600 kilometres - quite an accomplishment. Since the weight of the gasoline is such a tiny fraction of the car's mass, it does not contribute significantly to the mass that it has to move.
Now let's imagine a fuel called zip, which is ten times less energy dense than gasoline. In this case, the car's fuel efficiency is 1.5 km/l, and 30 kilograms of zip will move our car only 60 kilometres - not very convenient.
We may try to increase the size of the zip tank from 40 litres to 400 litres to bring our total range back up, but this doesn't work. Suddenly, our 1,200 kilogram car weighs 1,500 kilograms - the car's original weight plus the weight of 400 litres of zip. Since the zip has to move its own mass as well as the car's mass, the car's fuel efficiency falls still further. If we try to increase the size of the tank again to compensate, we further reduce the fuel efficiency.
At the same time that inefficiency plagues the car design, the zip refueling stations will have to have storage tanks ten times as big, and there will have to be ten times as many fuel trucks to refill them. In fact, as we've just seen, there will actually have to be more than ten times as many fuel trucks if the trucks are also zip-fueled and have to carry their own fuel supplies as well.
Yikes! For such a system to work, cars would have to become much, much smaller and lighter. However, there are physical limits to how small and light a car can be. The engine will still have to be made of various metals, which are heavy no matter how efficiently they're designed. That engine will have to sit in a frame strong enough to carry it, not to mention the driver, passengers, and cargo. Any frame strong enough to do this, not to mention strong enough to withstand the vibration of the engine, bumps on the road, and occasional collisions, will also be constrained in how light it can get.
Needless to say, if we had zip instead of gasoline, there's no way we would have built a transportation system of personal vehicles carrying their own fuel. Such vehicles would be extremely rare, affordable only to the very wealthy. The transportation infrastructure at large would favour trains for long-distance travel and walking/ cycling/ light rail for short-distance travel - exactly where we were a hundred years ago, before cars became our dominant mode.Once again, we are likely to find ourselves in an energy environment in the next several years where oil becomes too scarce to continue fueling our transportation network. Since no combination of alternate fuels can match oil's unique properties, we will be stuck with a transportation infrastructure we are no longer able to run.
In the meantime, we continue to add to that system with new suburbs, new warehouse stores on cheap farmland, and new commercial parks far from the centre of town.
Talk about being dense.