Regulators in the US have expanded their on-the-road emissions tests covering all makes and models of diesel cars following the dieselgate scandal involving Volkswagen.

The on-the-road emissions tests come after Volkswagen allegedly admitted in September that it installed software on more than 11 million cars worldwide to evade emissions standards, reported The New York Times.

The Environmental Protection Agency (EPA) is conducting the tests randomly and in real-world environment, rather than in laboratory settings to increase the chances of catching any major discrepancies.

"We are very anxious to find out if there are any other programmes out there."

EPA office of transportation and air-quality director Christopher Grundler was quoted by Seattle Times as saying: "We are very anxious to find out if there are any other programmes out there."

EPA will also coordinate with regulators in Canada to conduct the tests.

Last week, the first tests on brands manufactured by Volkswagen were completed. The authorities found the ‘defeat devices’ on about 10,000 VW, Audi and Porsche models, which were not earlier revealed by the automaker.

The automaker had contested the EPA’s claim, stating that the ‘defeat devices’ were not meant to evade emissions testing, reported Seattle Times.

Testing was previously carried out only in a laboratory setting, where a controlled ‘rolling road’ was used in place of actual asphalt.

The vehicle manufacturer was claimed to have been able to evade emissions standards as its four-cylinder diesel vehicles could identify when the car was in such a setting.

Only large trucks were previously put through on-road testing.

Following this scandal, testing is now extended to all diesel vehicles models from 2015 and 2016, and to any diesel vehicle that wants EPA certification.

This is to ensure that all vehicle manufacturers follow pollution rules and regulations.

The EPA’s testing process will also include spot checks on older cars in order to ensure that systems for pollution-control are still efficient.

Image: Volkswagen allegedly installed software to evade emissions standards. Photo: courtesy of Volkswagen.