Moral under the bonnet?

The worthy technologies that make today’s cars cleaner are mainly hidden from view - and for most people are not obvious even when you open the bonnet.

Sophisticated fuel management mechanisms can cut the numerous - and often poisonous - waste products coming out of the exhaust pipe, and better combustion means better efficiency and lower gas emissions too.

Compressed natural gas burns clean and generates low noxious emissions and particulates and a distribution network already exists - even though adaptation of cars and filling stations is necessary.

Hybrid vehicles combining two engines - usually one electric and one using petrol or diesel - can run quietly and with almost zero pollution in urban traffic and can even recuperate energy by rheostatic braking. They are also suitable for long-range travel - although two engines obviously raise costs and weight.

Fuel-cell motors operate on electricity that is constantly generated by combining hydrogen with oxygen through catalysis. Their only emission is water and they make little noise, but you will have trouble finding a filling station with a hydrogen pump.

Burning biofuels has the merit of putting to use plant material that has already absorbed carbon dioxide (CO2) from the air while it was growing, thus partially compensating for the emissions created by your car. Little adaptation is necessary for filling stations and biofuels reduce dependence on oil and other fossil fuels - as long as their production is sustainable and they do not compromise food production.

Special filters placed in the tailpipe can catch particulate matter, eliminating 90% of the health-threatening smog when designed and fitted as standard. When they become clogged, they have to be regenerated by a burning-off process so as to avoid damage to the engine from counter-pressure in the exhaust, but some are now being manufactured to last as long as the car.

Overall use of lighter materials can cut weight, reduce fuel consumption and limit emissions, but construction regulations still limit some more radical solutions.

So with this rich choice of technology, surely only a Philistine would fail to go clean? But strangely, at the European Motor Show there are only few people clustered around the Toyota Prius Luna, which for €26,000 will assure you of CO2 emissions of only 104 grams per kilometre you drive. What draws the crowds is the glitz of the Maserati Gran Turismo, emitting 330g CO2/km, the Bentley Continental GT Speed at 410g CO2/km, the Ferrari Scaglietti that pushes out 470g CO2/km - or, if you still have the €460,000 to spare after Christmas and the new year sales, the new Rolls Royce Drophead Coupé, whose 6.75 litre engine will emit only a relatively eco-friendly 377g CO2/km. Bonne route.

The worthy technologies that make today’s cars cleaner are mainly hidden from view - and for most people are not obvious even when you open the bonnet.