Bigger, more-powerful cars have negated the impact of tighter CO2 emissions regulations in the EU, a report by the bloc's internal auditor found Thursday.Since 2012, cars sold in the EU must meet targets for limiting CO2 emissions, but these had little impact as emissions from diesel vehicles since then held steady while there was only a small decrease of 4.6 percent for petrol vehicles, according to a report by the European Court of Auditors.