Reduce your road tax 20 June 2008 by Parkers Changes in April 2009 mean majority of drivers must pay more Only the greenest drivers will benefit High-emission cars will be hit hard The only sure fire way to reduce the cost of road tax is to drive a car that produces fewer carbon dioxide emissions. Only cars with 100g/km or less CO2 emissions qualify for free road tax. At the moment, drivers of cars with emissions between 101- and 120g/km can buy six months road tax for free but pay £35 for 12 months. This loophole closes in 2009 when the new road tax bands come into force. Opting for a diesel-engined car can reduce road tax costs as most diesels have lower CO2 emissions than their petrol equivalents, though you must remember diesels attract a 3% extra levy for company car drivers. Most automatic gearboxes push up CO2 output, so pick the same car with a manual gearbox to reduce emissions and save on road tax.