Part of the reason Volkswagen was able to cheat the federal government's emissions testing for so long was the test itself: standardised, free of variables, and easy to engineer around. In the wake of Dieselgate, the EPA is announcing an overhauled, actually-useful testing procedure.
According to the New York Times, the EPA is going to test all new cars — and 2015/16 diesel models — on actual roads. Previously, testing was done in a fixed location by putting the car onto rollers and entering test mode, which made it easy for the car's software to detect the test, and put on its good-boy no-emissions hat.
The on-road testing will apparently be far more randomised and unpredictable, which should make 'defeat devices' far harder to rig. It will basically involve driving the car on regular roads, but with a machine in the trunk hooked up to the exhaust, measuring emissions as you drive. It's the same kind of testing the EPA has done on large trucks for years, but now being rolled out across all passenger vehicles.
Road testing doesn't mean the end of lab testing, though: lab tests will stay as the official benchmark to meet emissions standards; the road testing is just to weasel out the cheaters.