Benchmarking against the best

My first 17 years in the automotive industry (at Volvo Technology) I worked in research and could together with my colleagues contribute to the technology improvement that now is used to develop the environmental improvement we realise today. Our research director, Lars-Göran Rosengren, constantly challenged us to benchmark against the best. We made efforts to find technologies of the best competitors to compare our in-house research and development to.

Now, as Environmental Director, I use the key data from other person transports to improve further. Our Volvo 7700 Hybrid bus is #1 in environmental performance, as I already written about previously. But, how does it compare to the environmental leader in person transports, biking?

The single most important contributor to the environmental load during the use phase is energy use (as defined in the EU directive for Green and Energy efficient Vehicles, read it here) and second is the carbon dioxide, followed by NOx and particulates.

The average European city/commuter bus has 20 passengers and drives in 20 km/h. I used the average data for fuel consumption 43 litre per 100 km for the diesel bus and 28 litter per 100 km for the hybrid bus.

When calculating the energy use per passenger kilometre data for the average European bus is applied.

For the bus the energy for the diesel fuel is used for the calculation and for the cyclist the energy content in the food required to maintain the energy balance is used. The average efficiency of the nutrition cycle converting energy in food to mechanical work is 20%. The bike is still in lead with 43 Wh per kilometre. But, our plans for further improvement will truly challenge the bike for the average passenger.

Second to energy use the, carbon dioxide contribute most to the environmental cost for society. Now, for the carbon dioxide, the diet of the cyclist is essential. In the graph below you will find data based on an diet of hamburgers. For a vegetarian the carbon dioxide emissions will become much less. But, the hybrid bus will become a vegetarian as well, when fuelled with biodiesel.

In the math race against the bike the hybrid bus now challenge the bike in carbon dioxide emissions, already when fueled on fossil diesel.

The data above is based on the average occupancy of 20 persons. For a traffic planer the relevant question might be:

Which occupancy of the bus is required to compete with the bike?

For that I have done the calculation below. The energy use for a pedestrian walking rapidly at 10 km/h and a cyclist biking at 20 km/h is compared to the average European diesel bus and the new Volvo 7700 Hybrid.

The total energy use is increasing for the increasing weight of the bus (about 3% per tonne) but the energy use per passenger is decreasing up to the maximum capacity of the bus. The hybrid bus has about 5 person higher passenger capacity than the standard bus. The energy use per passenger is hence 30 Wh per passenger kilometre for a fully occupied standard diesel bus and 18 Wh per passenger kilometre for the fully occupied Volvo 7700 Hybrid.

The answer to the question above is thus that it is more energy efficient to take the bus than to take the bike when there are more than 52 passengers in the standard diesel bus and more than 32 passengers in the Volvo 7700 Hybrid.

However, the difference is small and I need the exercise and will hence continue to take my bike as often as I can…

About volvobuses

Adjunct Professor of Catalysis at Chalmers University of Technology. Lives in Gothenburg, Sweden, with my wife and three daughters born in 1991, 1994 and 1997. Is a passionate runner.
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