The American government's commitment to reducing emissions and implementing a series of rigorous automotive standards has been underlined following a decision by the US Supreme Court to back the authority of the Environmental Protection Agency (EPA).

The Supreme Court gave its backing to the right of the EPA to block construction of a polluting facility when it felt that state regulation had not gone far enough in guaranteeing the reduction of emissions.

The tight 5-4 decision has been hailed as a test case for the ability of the EPA to assert its judgment in cases where pollution and emission standards are challenged.

Experts say the ruling is a boost to the power of the EPA, which can now overrule states in issues pertaining to the Clean Air Act (CAA) enforcement, including stringent standards such as the emissions controls prescribed for diesel engines by 2007.

The case in question centred on the EPA's right to veto construction of a power generating facility at the Red Dog Mine in Alaska, on the grounds that the 'best available control technology' was not being used to reduce NOx emissions.

The case was first brought to light six years ago, when the operators of the Alaskan mine announced plans to build a new diesel generator in order to boost production of zinc.

Ultimately Alaska's Department of Environmental Conservation (DEC) determined that the use of so-called 'Low NOx' controls and its accompanying 30 per cent emissions reduction would be acceptable, but the EPA insisted that a 90 per cent safeguard was necessary.

Victory for the EPA suggests that the balance of power has now shifted to the federal government, with the onus firmly on extensive emissions reduction technology.