fuel efficient cars

Diesel, petrol, electric or hybrid?

What you need to know to make the right choice

If you're buying a new car, you’ll need to think carefully about the type of fuel you choose.

  • Growing concern about air quality in cities, together with changes to emissions regulations and engine design, means that the right choice last time you changed your car may not be so right this time.
  • The main choice is still between petrol or diesel but other, cleaner alternatives, particularly plug-in hybrid and electric vehicles are growing quickly in popularity.

Exhaust emmissions

Climate change and air quality

It's impossible to talk about fuel choice without considering the sometimes difficult to balance challenges of climate change and air quality in towns and cities.

  • Cars contribute to climate change through their emissions of CO2.
  • The amount of CO2 produced is directly related to the quantity of fossil fuel burnt, so better fuel economy = lower CO2 emissions.
  • The exhaust from cars burning fossil fuels also contains pollutants like nitrogen dioxide (NO2) and particulate matter (soot) which are linked to asthma and other respiratory problems.
  • The amount of pollution depends on the fuel and the age of the vehicle – petrol's cleaner than diesel and newer vehicles are cleaner than older ones.

Euro standards

Since 2001 diesel's better economy and lower CO2 emissions has been rewarded through CO2-based car tax, while the government has relied on increasingly stringent ‘Euro’ emissions standards to tackle exhaust pollution.

Unfortunately, actual exhaust emissions in normal, 'real world' driving have turned out to be considerably worse than predicted by the official tests and Euro standard limits.

  • The first 'Euro' standard, Euro 1 came in in 1992 and resulted in the universal fitting of catalytic converters on petrol cars.
  • Euro 5, from 2009, set limits on particulate emissions that effectively required diesels to be fitted with a diesel particulate filter (DPF).
  • Comparing cars of the same age, diesels have historically been more polluting but Euro 6, from 2014/15, set broadly similar emissions standards for both petrol and diesel.
  • The Euro 6 test became more stringent from September 2017 with the addition of an extended on-road emission test known as Real Driving Emissions or RDE which is being introduced in two steps.

Low Emission Zones

There are many other causes of pollution in our cities besides cars – trucks, buses, taxis, trains, domestic heating, industry and so on – but in the face of growing traffic volumes and congestion, city authorities are looking more and more at vehicle access restrictions or charging schemes alongside other measures to tackle local air quality issues.

Measures are more likely to target older diesels:

  • The London LEZ started in 2008 for large, commercially operated diesel vehicles like buses, lorries and coaches but was extended in 2012 to cover vans, minibuses, horseboxes, motor-caravans, utility vehicles, pick-ups and more.
  • The T-charge, an environmental 'toxicity charge',  will start in October 2017 and apply to pre-2005 petrol and diesel cars entering the London congestion charge zone.
  • The London ULEZ, due in force from 2019 or 2020, will impose additional charges on pre-2015 diesels and pre-2005 petrol cars.

Petrol vs diesel

  • Petrol cars generally use more fuel than diesel, and produce more carbon dioxide (CO2).
  • Diesel cars produce more toxic emissions depending on the ‘Euro’ standard that applied when the car was new.
  • Petrol and diesel servicing costs are similar. Both require servicing, particularly an oil change, at least once a year.
  • Diesels have a narrower rev range but lots of torque making them better suited to towing and more flexible on motorways or hills where fewer gear changes may be required.
  • Petrol is a bit cheaper at the pumps but diesel's better fuel economy should mean annual savings on your fuel bill. If you have to pay extra for the diesel car in the first place then it could take several years, depending on your annual mileage, to recover through lower fuel costs.
  • Diesels, particularly pre-2015 models, are increasingly likely to face charges or be restricted from entering major cities.
  • Diesels fitted with a Diesel Particulate Filter (DPF) need regular long runs, some of which must be at high engine speed to clean (regenerate) the filter so are not suited to mostly short, local journeys.
  • Newer diesel cars use AdBlue - an exhaust fluid which breaks nitrogen oxide gas down into harmless nitrogen and water vapour to reduce your car's emissions.
  • From April 2017 first year car tax is based on CO2 emissions, so diesel's may initially be cheaper, but a flat rate of £140/year applies equally to petrol and diesel from the second year.

Other Choices

Plug-in Hybrid (PHEV)

Plug-in hybrids combine a petrol or diesel engine, with electric motors and a battery pack that can be charged externally giving them a limited but practical range in electric-only mode. 

  • During stop, start driving the battery is also charged by the engine and a process called 'regenerative braking' which slows the car down by converting kinetic energy into stored electrical energy. 
  • For high speed motoring the battery/electric motor may assist the engine.
  • PHEVs approved as an ultra-low emission vehicle by the Office for Low Emission Vehicles qualify for the London Congestion Charge Ultra Low Emission Discount (ULED).
Electric (EV)

With zero emissions at the point of use, electric vehicles are ideal for use in towns and cities but their limited range and the need to plug in to recharge means that they will not be suitable for everyone.

  • Range is improving with advances in battery and charging technology.
  • Government is committed to improving the availability of recharging points.
  • Electric vehicles qualify for the London Congestion Charge Ultra Low Emission Discount (ULED).
  • ‘Range extender’ electric vehicles (E-REV) have a small internal combustion engine that operates as a generator to recharge the batteries so that range isn’t limited to the capacity of the batteries.

If you're thinking about going electric, try to arrange an extended test drive so that you can be sure that range and charging needs suit your lifestyle.

The best choice for you?

  • If you cover a high mileage and the bulk of your driving’s on motorways, then a new diesel (with a DPF) is still a good option.
  • If your driving is predominantly short journeys on local roads, then petrol will be more suitable than a diesel because Diesel Particulate Filters don’t like short journeys.
  • If you live and drive mainly in a large town or city, then an EV, or PHEV would be the better choice.
  • Outside of a town or city the suitability of an EV or PHEV will depend on how far you have to drive and access to recharging points.

Everyone’s personal circumstances are different but this chart  should help you narrow down your choice.

  Petrol Diesel (Euro6) PHEV EV
 Living/driving mainly in a city/large town - -- + ++
 Living/driving mainly in the country - low mileage ++ - ++ ++
 Living/driving mainly in the country - high mileage + ++ + -
 Living in the country/regularly driving into the city + - ++ 0
 Mostly motorway/high mileage + ++ - --
 Regular towing + ++ + --
 Living in a remote rural location + ++ + --

updated 29 January 2018

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