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4
A low-carbon transport system using low width cars
The fuel consumption of a road vehicle is determined by three factors:
a)
The work required to overcome the resistance to motion and acceleration, which is mainly determined by
the size, weight, shape and speed of the vehicle
b)
the efficiency which the engine and transmission converts the chemical energy in the fuel into useful work
to accelerate and move the vehicle
c)
the kinetic energy wasted during braking
Despite some developments in engine design and control systems, vehicle streamlining and regenerative braking
systems in recent years, there has been limited progress in reducing fuel and CO2 emissions from cars. These
initiatives have been compromised to some extent by the requirements to meet emission legislation and the
greater vehicle weight required for safety and greater use of ancillaries such as air conditioning.
17
Weight
reductions have also been limited by strong consumer marketing to bolster public demand for larger and higher
performance vehicles beyond that of mere practicality, since larger vehicles provide greater prestige value for
the owner and greater profit margins and turnover for the motor industry
Whilst there is still scope for improvements in engine efficiency and reclaiming braking losses, peak engine
efficiencies can already be in excess of 50% and significant further gains attained this way are fundamentally
limited through thermodynamic constraints. Under real world conditions engine efficiencies are far less, and to
approach these levels in practice requires ever more complex and costly technologies, which increases the life
cycle environmental burdens during the manufacture and disposal of the extra components. Therefore, to obtain
major reductions in fuel use, or electricity in the case of electric cars, it is necessary to radically change the size,
weight, and shape of the vehicle or the speed at which it travels.
At the same time as cars have been getting heavier, demographic changes are leading to either smaller families
or single occupant households. As a result, the number of occupants per car is decreasing
18
and cars are getting
significantly heavier in relation to the people they carry. A typical vehicle will need to carry approximately 20
times the weight
19
and 100 times the volume
20
of the driver it carries. This belief has been encouraged by strong
consumer marketing to bolster public demand for larger and higher performance vehicles beyond that of mere
practicality, since larger vehicles provide greater prestige value for the owner and greater profit margins and
turnover for the motor industry. This is a grossly inefficient way of transporting people around, and there is
clearly a vast potential to save fuel and thereby reduce CO2 emissions in the private vehicle sector.
Obviously, one method to reduce these ratios is to share the trip with other travellers as in the COAST system,
but many drivers will still insist on their privacy. The other method is to make the vehicle radically smaller to
suit the likely number of people to be using it; we examine this second possibility in this section. The smaller
size would also reduce its overall cost making alternative technologies more affordable. Moreover, the much
lower fuel requirements of these vehicles could be more easily met from sustainable resources such as
renewable biomass or overnight nuclear electricity which would reduce CO2 emissions to near zero.
17 The official fuel consumption figures and emission legislation in the European Union do not take into account the additional load
imposed by ancillaries
18 The average number of occupants per car has fallen slightly, from 1.60 in 1995/97 to 1.58 in 2006,
In 2006, 60 per cent of cars on the road had only one occupant. 85 per cent of both commuting and business car trips had only the one
occupant. Transport trends 2008
19 (person+car)/person , using Ford Focus1.6 TDCi (2009) as typical vehicle 1357 kg, and average UK person weight of 73.2 kg
20 approximate calculation assuming typical frontal area of about 2.25 m2 x average weighted length of 3m x 1.2 m height of body and
using 80 litres (0.08 m2 ) for person volume based on 70-75kg weight with specific density slightly less than 1
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