AVERAGE speed cameras are being installed on the Forth Road Bridge after transport bosses realised drivers were already slowing down to 40mph to stare at the construction of the new Queensferry Crossing.

The speed limit on the existing bridge is to drop from 50mph to 40mph in the spring, with average speed cameras installed along three miles of the A90 and M90 until the completion of the new crossing, which is due to open in by the end of 2016.

David Climie of the Forth Replacement Crossing Team said drivers are already slowing down to look at the construction of the adjacent Queensferry Crossing.

Mr Climie told Holyrood's Infrastructure and Capital Investment Committee: "We decided that we would have it in operation right over the Forth Road Bridge as well because one thing we've specifically noted is that traffic is slowing down on the Forth Road Bridge looking at what we're doing.

"There's no doubt that there's been a lot of distraction there so it makes sense to have the 40mph average speed limit to control the traffic flow right through that entire area.

"The difference between the three miles at 50mph and 40mph is less than one minute in travel time, so we think the impact is going to be very insignificant."

In October it was announced that the cost of the new crossing will be £50 million below the previous budget estimate of between £1.4 billion and £1.45 billion.

Meanwhile, transport minister Derek Mackay said he was open to rolling out more average speed cameras across Scotland's road following the success of the A9 scheme between Perth and Inverness.

The cameras have cut speeding and road deaths on the notorious road since launching in October.

Although the cameras, which measure a driver's average speed over set distances, have been in use on the A77 in Ayrshire for a decade some campaigners were opposed to their use on the A9 because it would increase journey times and frustration among motorists.

Mr Mackay said: "The A9 shows public opinion has changed. The principle is now far better established. There is an important message for the rest of the country.

"Average speed cameras, if deployed in the right places, can help assist road safety. Extra journey times are worth paying for a safer route."

There is thought to have been only one death on the A9 in the last four months compared to eight in 2014 and nine in 2013.