most densely packed. The number of nearby vehicles that are active can be
sensed anonymously by fitting in every vehicle a radio transmitter/receiver
(like a very cheap mobile phone) that transmits little radio-bleeps at a steady
rate whenever the engine is running, and that counts the number of bleeps
it hears from other vehicles. The congestion charge would be proportional
to the number of bleeps received; this charge could be paid at refuelling
stations whenever the vehicle is refuelled. The radio transmitter/receiver
would replace the current UK road tax disc.

126hydraulics and flywheels salvage at least 70% of the braking energy. Compressed
air is used for regenerative braking in trucks; say “hydraulic
launch assist” captures 70% of the kinetic energy. [5cp27j]
The flywheel systemof also captures 70% of the kinetic
Electric regenerative braking salvages 50%. Source: E4tech (2007).

Electric batteries capable of delivering 60 kW would weigh about 200 kg.
Good lithium-ion batteries have a specific power of 300 W/kg (Horie et al.,
1997; Mindl, 2003).

the average new car in the UK emits 168 g CO2 per km. This is the figure for
the year 2006 (King, 2008). The average emissions of a new passenger vehicle
in the USA were 255 g per km (King, 2008).

The Toyota Prius has a more-efficient engine. The Prius’s petrol engine uses
the Atkinson cycle, in contrast to the conventional Otto cycle. By cunningly
mixing electric power and petrol power as the driver’s demands change, the
Prius gets by with a smaller engine than is normal in a car of its weight, and
converts petrol to work more efficiently than a conventional petrol engine.

Hybrid technologies give fuel savings of 20% or 30%. For example, from
Hitachi’s research report describing hybrid trains (Kaneko et al., 2004): high-
efficiency power generation and regenerative braking are “expected to give
fuel savings of approximately 20% compared with conventional diesel-powered

127Only 8.3% of commuters travel over 30 km to their workplace. Source: Eddington
(2006). The dependence of the range of an electric car on the size of
its battery is discussed in Chapter A (p261).

Lots of electric vehicles. They are all listed below, in no particular order.
Performance figures are mainly from the manufacturers. As we saw on p127,
real-life performance doesn’t always match manufacturers’ claims.

Th!nk Electric cars from Norway. The five-door Th!nk Ox has a range of 200-
km. Its batteries weigh 350 kg, and the car weighs 1500 kg in total. Its energy
consumption is approximately 20 kWh per 100 km.

Electric Smart Car “The electric version is powered by a 40 bhp motor, can go-
up to 70 miles, and has a top speed of 70 mph. Recharging is done through a
standard electrical power point and costs about £1.20, producing the equiv-
alent of 60 g/km of carbon dioxide emissions at the power station. [cf.
the equivalent petrol-powered Smart: 116 g/km.] A full recharge takes

Figure 20.37. Th!nk Ox. Photo from