The Extra Mile

The Extra Mile

Let’s take something of a drive into the future, and consider the principle of economy driving when cars have become electric, and potentially fully autonomous. Maybe general attitudes will be that electric cars are very efficient and economical, and the energy they use so cheap, that saving fuel won’t really be considered relevant. Range and charging facilities surely will be important though, but that dream scenario of low running costs could be revealed as an illusion. 

Today’s domestic electric energy enjoys very low taxation of just five per cent VAT. Compare that with excise duty of 58p a litre on pre-tax diesel costing around 56p ñ effectively a 100 per cent duty rate, with 20 per cent VAT added on top. That means 7p a mile in tax alone with a 50mpg car, which generates some £28 billion annually for UK Government spending. That income will have to be replaced, one way or another, as fossil fuel sales inevitably fall. Taxation on charging electricity for road transport, at a much higher rate than domestic electricity, using a ìsmart meterî to measure usage, is a strong possibility. Alternatively, it might come from a road charging scheme, which will need to be set at around 6p to 8p per mile for cars, just to cover that lost tax income. So the energy costs of electric cars may be little different from diesel costs today, and will remain significant, and economy driving well worthy of consideration, too.

The whole proposition of autonomous cars takes us into some fascinating territory though. What choice of driving styles will be offered in future autonomous cars, presuming that a choice will be given? Will we get offered maybe mild, moderate, aggressive and even Tesla’s Ludicrous? With autonomous cars, what opportunities will be available, should you want to take control, by cancelling out the autonomous technology. Would such an option offer any real prospect of out-performing the fuel economy of the autonomous settings? Well of course the energy recovery systems that recharge the battery with accelerator lift-off is one of the main keys to the efficiency of hybrids and plug-ins, and most offer a selection of recovery level settings. They range from minimal changes to normal friction braking, and thus minimal energy recovery, all the way to ìone-pedalî driving, where the strong deceleration from high level energy recovery makes conventional braking virtually redundant, aside from emergencies. This would still be, in effect, when you chose to take the wheel, but the benefits of lifting off early and using anticipation to avoid braking are much reduced, because up to 60 to 70 per cent of the kinetic energy of the car’s weight and speed can be recovered, and fed to the battery, instead of dispersed as the heat from braking friction.

But speed will always be a critical factor in terms of battery range and fuel costs, and there’s no escaping the effects of aerodynamic drag, even with slippery cars like the Tesla. As speeds rise, unrecoverable energy becomes more and more significant. Will autonomous cars attempt to drive ìup to the applicable legal limit,î or will they offer lower cruising speed options, for better economy and greater range? Many people would maintain that they have every right to travel at a steady 50mph in a 60mph limited road, so long as that is not deliberately obstructing other traffic. Will it be possible for occupants to set their desired cruising speed, if they want to reduce energy usage, and extend the battery range? It might seem likely that intelligent autonomous cars, when presented with any destination, will probably adjust their speed and performance levels to suit the battery capacity, and/or advise the ìdriverî of any need for recharging en route. Or maybe they may simply offer a cruising speed option that should avoid that necessity and leave you to monitor the range as you drive.

It certainly is a complex business all-round, and there’s a fair possibility that it will all happen somewhat more slowly than the media (and product makers) tend to forecast; but it’s all food for thought. If our forecast of future electricity costs is correct, the ìcleanî diesel car will, on open roads and motorways, surely still represent a highly viable alternative to tomorrow’s electric world!

Victor Harman 

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