The Flying Shingle
Focus on the Future
The Search For A Green Vehicle: Toyota Prius Versus VW Jetta TDI
by Michael Mehta
Monday, February 28, 2011

The concept of a green automobile is an oxymoron, and the greenest modes of transportation include walking, cycling and public transportation. But if you wish to drive a car, how can you minimise the impact?

In 2001 the Toyota Prius was first introduced to North America.In 1997, Volkswagen reintroduced a clean diesel version of a top seller; namely the VW Jetta TDI. Which car is greener and how can we make reasonable comparisons between consumer products that perform the same function yet do so differently?

The Toyota Prius and the VW Jetta TDI represent two top choices for consumers interested in fuel efficiency and environmental performance. Data from Natural Resources Canada on these two vehicles showed the following:

2011 Prius: Engine type: 1.8 litre/ four cylinder; Fuel cost per year: $798; Litres per year: 760. Consumption, litres per 100 km: 3.7 city/4.0 highway.

2011 Jetta TDI: Engine type: 2.0 Litre/four cylinder; Fuel cost per year: $1334; Litres per year: 1160; Consumption, litres/100 km: 6.7 city/4.7 highway

However, real world driving conditions and driver behaviour often yield different results, and in the Sept. 24 2008 issue of Popular Mechanics magazine, a two-day comparative test between the Toyota Prius and Volkswagen Jetta TDI was published.

Day one of the test involved city driving exclusively. The Prius performed better, achieving a fuel consumption of 5.3 litres per 100 km compared to the Jetta TDI’s 7.4 litres per 100 km.

Day two of the test was primarily highway driving. The testing team discovered that the Jetta TDI slightly beat the Prius (5.2 litres per 100 km versus 5.3 litres per 100 km).

Both the Prius and the Jetta TDI are engineering marvels, with the Prius relying upon a gas electric hybrid system, while the Jetta TDI produces gobs of satisfying torque from a diesel engine. Clean diesel engines are quite different than the smokers and stinkers of the past, and they burn industry-standard fuel that has gone through desulphurisation and dearomatisation processes.

When it comes to tough air quality standards, California’s Environmental Protection Agency leads the pack. Both the Prius and the Jetta TDI are fully compliant under these, and Canadian, regulations, and are certified to meet exhaust and evaporative emissions standards for compounds like methane, carbon monoxide, nitrogen oxides, particulate matter, carbon dioxide etc.

The art and science of life cycle analysis is a tool that can be used to compare products. Classic examples of such comparisons include analyses of cloth versus disposable diapers, glass versus plastic bottles, wind power versus solar power, and so on. These analyses are connected to the concept of "ecological footprint" and when it comes to comparing vehicles several factors are considered including the sourcing of raw materials, the energy involved in processing them, the generation of toxic byproducts, shipping and packaging, disposal of components, etc. This cradle-to-grave approach is considered the gold standard for doing such assessments.

Unfortunately, life cycle analysis can also be subverted for political and commercial gains.

A prime example of this is a 2007 report entitled "Dust to dust: The energy cost of new vehicles from concept to disposal" by CNW Marketing Research of Oregon.

This highly deceptive and much discredited non-peer reviewed report asserted that the Toyota Prius has a worse impact on the environment than a Hummer, and that the mining, refining, processing and assembly of nickel metal hydride batteries used in the Prius outweighs the significant fuel savings associated with this vehicle. Subsequent studies by researchers at MIT, Carnegie Mellon University, and the world-class Argonne National Laboratory have contradicted this analysis.

Although the CNW Marketing Research study represents a form of intellectual fraud, and it has become an urban legend, there are indeed some legitimate questions that need to be answered regarding the environmental impacts of batteries in hybrid and fully electric vehicles. On a global basis, batteries in general consume approximately six per cent of the world’s nickel supply of 1.55 million tons per year. Most nickel is used for stainless steel, alloys, and for electroplating.

Furthermore, not all batteries are equal in terms of their environmental impacts. Lead acid and nickel cadmium batteries are considerably worse than nickel metal hydride batteries, and the environmental performance of lithium ion batteries is the best to date.

In closing, both the Prius and Jetta TDI perform very well in terms of fuel efficiency, meet emission standards, and represent two viable options for green consumers. The Prius will probably cost less to operate in the first 10 years, while the Jetta TDI avoids the environmental downside of using a large array of batteries.

In 2011 Nissan introduced their new five-door, mid-size hatchback known as the Leaf. This 100 per cent electric vehicle uses a lithium ion battery pack, and it is expected to have a range of 160 km. Green consumers have a new set of considerations to weigh, and I am delighted that environmental performance is once again on the radar screen. 

Dr. Michael Mehta is a sociologist who focuses on environmental and health risk issues.

 Opinions expressed in this column will usually be those of the author and do not necessarily reflect those of The Shingle.

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