Harsh accelerations and heavy braking use considerably more energy and lead to more tyre wear than a smooth slow acceleration and limited brake action. Looking and thinking ahead can allow more gentle acceleration and braking and a more comfortable ride. On long-distance journeys, reducing the top speed reduces air resistance (drag). As air resistance increases with the speed squared, even small reductions in top speed translate to significant fuel or energy savings over long trips. Regularly keeping tyres pumped to the top of the manufacturer approved pressure range will reduce rolling resistance and translate to fuel or energy savings too (the manufacturer approved pressure range is in the manual or on the tyre pressure sticker often on the door frame or by the fuel filler cap). Frequent use of the accelerator and brake pedal on a journey probably indicates a driving style that consumes more fuel. Holding back and keeping a steady pace could make a useful saving.
In a petrol, diesel or hybrid car, harsher accelerations and higher cruising speeds result in higher fuel consumption and higher costs at the petrol station pumps. It also means higher tailpipe emissions. Consistently keeping the vehicle in a suitably high gear (for vehicles with a manual gearbox) will improve efficiency: driving in a lower gear with high revs means the engine is burning more fuel than is needed to travel the same distance. In an automatic there may be an eco mode which keeps the engine revs to a minimum (sports mode is rarely effective at saving fuel).
In an electric car, harsher accelerations and higher speeds translate to higher electricity consumption and higher costs. Many models feature an eco mode for the most efficient use of the powertrain. If more regenerative braking is required then some will offer a mode with additional regeneration that may help a little on some start-stop journeys or where there are many hills.
If the car features a trip computer and a fuel efficiency monitor then it is possible to see the effect of different driving styles on fuel or energy consumption. Trying out a day or two of different driving styles, such as slower accelerations and braking and reduced top speeds, will show up on the trip computer with changes to the efficiency figure (mpg or l/100km for a conventionally-fuelled vehicle or m/kWh or km/kWh for an electric vehicle).
Why not test this out on a regular trip to see if driving differently will improve the mpg or l/100km values each time? Consider it a driving challenge!
Working out the fuel or energy efficiency (or checking the trip computer)
In a fuelled car (petrol or diesel). Fill the car up full and note down the current odometer reading (total miles or km). Drive as normal or with an improved driving style. Fill the car up full again and note down the volume of fuel needed to fill up the car and the new odometer reading (total miles or km). Work out the distance between refuelling (second odometer reading minus the first).
For mpg – miles per gallon – distance in miles divided by fuel used in gallons (1 UK gallon is 4.546 litres, 1 US gallon is 3.785 litres) – higher mpg is better.
For l/100km – litres per 100 kilometres – fuel used in litres divided by distance in kilometres times 100 (1 mile is 1.609 km) – lower l/100km is better.
Some trip computers are not as accurate as they could be. Comparing actual efficiency to that in the vehicle manual may suggest how much further improvement in fuel consumption is possible. However, some manufacturers have exaggerated efficiency claims in the past and achieving the efficiency on the technical specification could prove to be too hard a task. Previous experience with hire cars suggested that there could even be some fuel consumption variation between similar or even identical models.
In an electric car. Charge the vehicle up to the normal set point (e.g. 80% charge, 90% charge or whatever is recommended). Note down the current odometer reading (total miles or km). Drive as normal or with an improved driving style. Charge the vehicle up to the same set point as before and note down the electricity used to complete the charge session and the new odometer reading (total miles or km). Work out the distance between refuelling (second odometer reading minus the first).
For m/kWh – miles per kilowatt-hour – distance in miles divided by electricity used in kilowatt hours – higher is better
For km/kWh – kilometres per kilowatt-hour – distance in kilometres divided by electricity used in kilowatt hours (1 mile is 1.609 km) – higher is better
Improved efficiency in electric motoring leads to a greater driving range that is of practical benefit too. A slower, smoother journey could even turn out to be quicker if a charging stop is not required.
Charging for the future
Recently in the UK there has been a consultation on the future of road tax. How to equitably charge road users for paying for the upkeep and maintenance of the road network given that traditionally much of the tax for roads has come from fuel duty. Are there lessons from Catholic social teaching that could apply here? Catholic social teaching encourages us to consider life and dignity, the common good, responsibilities towards social justice, consideration of the poor, the dignity through work, solidarity and fairness with regards the world’s resources, and care for God’s creation. The transition to electric motoring means there is an opportunity to design a road tax system from scratch which is fairer and responsible.
Considering these aspects, road tax should be designed to incentivise good behaviours and environmental benefit, as well as reflect the damage each vehicle does to the road infrastructure and local environment that must be put right by government expenditure. Or seen another way, it should provide a reasonable route for addressing the harms caused by road transport (including those harms caused by urban pollution on human health and from greenhouse gas emissions on climate change). A future dominated by electric vehicles is not one completely free from emissions, even if there are no tailpipe emissions. The emissions of an electric vehicle fall into two categories: up-front or capital emissions and running or operating emissions. Currently embedded carbon (that is carbon dioxide equivalent emissions from manufacture and supply, from mine to showroom) is not considered by most taxation bodies and this constitutes a large proportion of electric vehicle overall emissions. Governments may tend to focus on how to fund road maintenance. Considering this aspect alone would suggest taxing against vehicle weight and distance travelled (it would be too complicated to include driver behaviour or driving style as described in the article above, however some of this may be taxed through taxes on energy). Whilst electric vehicles do not emit tailpipe emissions, the electrical energy used does have a lifecycle emissions value to reflect the energy source and the transmission and distribution emissions: greenhouse gas emissions occur away from the vehicle. Then there are still particulate emissions from, in particular, tyre wear (and to a lesser extent to brake wear). Particulate emissions of this nature could still create harm to human health and to the local environment. Taxing embedded emissions (emissions released from mine to showroom) may lead to differential tax rates for different vehicles that reflect the environmental damage from the manufacture and supply chain. This could incentivise good purchase decisions. A tax of this sort does not require motorist effort so could be easily managed during the vehicle model approval process (certification). A tax on efficiency could lead to an incentive to select vehicles that have higher distance per unit energy – e.g. km per kWh – over those that don’t. Other options for taxation could include those that promote dignity through work and ethical purchasing, perhaps incentivising local manufacturing or recycling of materials.
Considering embedded carbon is a suitable method for addressing some of the harms and could form a useful part of a future tax system as it will tax luxury cars more since the embedded carbon is generally higher for manufacturing involving more steps and more complexity. It will also push manufacturers to address the hidden (and very real) emissions side of the vehicle lifecycle which is currently ignored by most tax regimes and by most commentators.
Living Laudato Si' 