Newly-installed speed cameras on one of Scotland's busiest roads could provide environmental gains as well as improving road safety, MSPs have been told.

Average speed cameras have recently gone up along much of the A9 in a bid to cut the accident rate on the road, which links Perth and Inverness.

Gina Hanrahan, climate and energy policy officer for WWF Scotland, said that by encouraging drivers to slow down, these could be "very effective" in cutting emissions.

She told MSPs on Holyrood's Rural Affairs, Climate Change and Environment Committee that the cameras were "actually a very effective emissions abatement opportunity".

Scotland has now failed to meet its targets on greenhouse gas emissions for three years in a row, with Ms Hanrahan stating emissions levels in the transport sector had not changed significantly from the 1990s.

She referred to the speed cameras which have been installed on the A9 and said: "We need to think about how we can roll that out more widely, and that delivers safety wins as well as emissions wins."

She also raised the prospect that more controversial measures - such as the introduction of road user charging - may be necessary in the future to help Scotland meet increasingly tough emissions targets.

Ms Hanrahan said WWF had been "disappointed" that the targets have been missed for the last three years as she warned it would be harder to meet future targets.

"As we move through 2014, 2015 and beyond that, the targets are getting increasingly challenging to deliver," she stated.

"We need to see government come forward with intensified policy effort.

"We have seen variable progress across different sectors of the Scottish economy, we've seen excellent progress on renewable electricity particularly.

"We see a need to redouble effort now in other policy areas to intensify efforts on, for instance, energy efficiency, on transport, on areas such as renewable heat, in order to hit those challenging targets."

She suggested later: "We need to start having conversations, perhaps about workplace parking levies, about increased parking charges, road user charging. These have all been potentially politically difficult topics.

"But we need to start having conversations now so we can build support for what might be politically challenging things."