David Climie, of the Forth Replacement Crossing Team, told MSPs he had “no doubt” the massive building project was proving a distraction for traffic.

Now bosses are so concerned about motorists slowing down to admire the new crossing that they are cutting the speed limit on the neighbouring Forth Road Bridge from 50mph to 40mph from the spring.

Average speed cameras are also being installed on part of the A90 and M90.

David Climie said: “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.”

Mr Climie told the Scottish Parliament’s infrastructure and investment committee that the project remains on schedule and within the budget of £1.35bn to £1.4bn.

He added: “There’s still a possibility – and I couldn’t put it any stronger than that – that we may be able to get some further savings yet.”

Mr Climie said the crossing would be fully open to traffic at the end of 2016.

When it is finished, the 1.7-mile structure will be the longest three-tower, cable-stayed bridge in the world.