As it promised in September, the Environmental Protection Agency is expanding on-road emissions tests for diesel cars in the wake of the Volkswagen emissions scandal. Previously tests were conducted in laboratory settings, allowing Volkswagen to use "defeat devices" on more than 11 million vehicles that could identify when they were under scrutiny, and adjust their emissions accordingly. The New York Times reports that the new tests will be carried out by the EPA and its Canadian equivalent at random and in real-world road conditions for all future makes and models of diesel-engine cars.

Volkswagen cars have already had on-road tests

"We are very anxious to find out if there are any other programs out there," said Christopher Grundler, the director of the EPA's office of transportation and air quality. On top of the 11 million vehicles implicated in the original scandal, at least 10,000 cars sold by Porsche, Audi, and Volkswagen were found to have emissions-cheating software installed in a second round of on-road tests completed last week. For now, no other car manufacturer has been found using similar defeat software, but the governmental body is being deliberately vague on what the new tests will entail to stop car makers from following Volkswagen's lead. "Manufacturers have asked us what the test conditions would be, and we've told them that they don't have a need to know," Mr. Grundler told The New York Times. "It will be random."

The New York Times describes on-road emissions testing as using a "Rube Goldberg-type machine" that sits in the trunk of vehicles to measure gases emanating from their exhaust. Regulators say that the technology, in use for several decades, is less accurate than lab testing in terms of discerning the exact output of pollutants. Despite these inaccuracies, European regulators are planning to use a separate emissions test cars must pass when it starts on-road testing in 2017. North American regulators, on the other hand, will be using road tests — which will be used in conjunction with lab tests — primarily to catch cheaters and dissuade car makers from installing defeat software.

Manufacturers "don't have a need to know" about the new tests

North American lab testing rules are already more stringent than those of European regulators. Where European manufacturers can submit not-for-sale cars with aerodynamic modifications or fewer seats to make them perform better in tests, the EPA measures emissions of both preproduction vehicles and those that are on the road. The proposed European rules have also been criticized for not going far enough, allowing cars to put out more than double the amount of nitrogen oxides during road tests as lab tests, and not testing for emissions during engine-taxing cold starts.

In addition to the 11 million Volkswagens that emitted more nitrogen oxides than they reported, the company today admitted that the fuel economy and carbon dioxide readings on 800,000 vehicles were also falsified. The EPA has been accused of shooting itself in the foot by opposing rules that could've helped it uncover Volkswagen's deception, but the new on-road tests — which will focus first on 2015 and 2016 models of diesel cars and be standard for all cars wishing to certify for road use in the future — should help cut down on the ways car makers can bypass environmental rules.