The US Environmental Protection Agency (EPA) has established the first new set of emission standards for highway motorcycles for 25 years.

Included in the rules for the first time are standards for small scooters and mopeds, as the Agency seeks to ensure emissions are brought under control.

According to the EPA, motorcycles produce more harmful exhausts per mile than cars, with the introduction of improved technologies set to cut this.

The EPA says manufacturers will be required to reduce hydrocarbons and nitrogen oxides by 60 per cent, using secondary air injection, electronic fuel injection systems and catalytic converters.

Meanwhile, a growing number of American states appear to be considering implementing the strict emissions regulations that apply in California.

Several states are reported to be interested in California's heavy-duty on-road diesel emission standards, particularly if the EPA is forced to delay plans to implement the standards nationwide.