It’s done. It’s finished. And it’s rather beautiful. There’s obviously still a few bits and pieces to be done before today’s official opening, but sitting in the headquarters for the Queensferry Crossing, the project director is feeling pretty satisfied on the whole. David Climie has been here overseeing the building of Scotland’s newest bridge for the last seven years and, on the cusp of its opening, he feels two things: pride at the things that went right; sadness at the things that went wrong.

The Rosyth HQ, where the Forth Crossing Bride Constructors have been based since 2010, is a pretty makeshift place: essentially just a group of portable buildings piled on top of each with Climie’s office at the top. However, for the project director it has been a kind of home and he has spent a lot of time here over the last few years, which is just the way he likes it. When he was growing up in Perth, he built bridges with meccano. When he was on holiday from school, he did work experience on bridges. And when he’s on holiday, he goes and looks at bridges. He is a bridge fanatic, a bridge geek.

He is also a forceful defender of his newest baby. Climie has been involved in, or responsible for, the building of many bridges around the world, including the Kessock Bridge in Inverness as well as bridges in China, the US, and elsewhere, but the Queensferry Crossing is special. It’s the first one where he has been in charge of the whole project – in this case, responsible for looking after taxpayers’ money and effectively representing the Scottish Government and making sure the job is done well and on time.

So how has he done? For a start, Climie is proud of the fact he has come in under budget, even though some of the savings were circumstantial. He is also robust about the delays to the build - the original target was December last year, but Climie says the hold-ups are the equivalent of being two hours over on the renovation of a house. And he is honest about how the death of one of the workers, John Cousin, affected him: it made him consider what he was doing and lessons, he says, will be learned.

Climie is also in absolutely no doubt that the new crossing was needed. “The key problem with the old road bridge was the suspension cables,” he says, “the washing line that holds up everything. There was lots of corrosion inside and some wires had broken. If that keeps going, you will get to a dangerous point. The cables could be replaced, but it would have meant closing the bridge for two to three years.”

But, if the cables on the old bridge were in such a bad way, how come it will remain open for buses, cyclists and walkers? Climie says that is because, with cars diverted to the new crossing, most of the pressure will be off the old road bridge and it will last much longer. “We did more analysis and said right, if we take the bulk of the traffic off of it, and we dehumidify the cables to slow down the rate of corrosion, potentially, there can still be a use for the Forth Road Bridge, and it was decided that yes, it could be used for buses, taxes, and cyclists.”

The fact that the old road bridge could be saved was also one of the reasons the budget has come down from the original estimate of £3 to £4billion to the actual cost of £1.4 to £1.6billion. “If we’d had to close the Forth Road Bridge,” says Climie, “we were looking at a budget of £3-4bn to mothball it and transfer everything to the new bridge, but we brought it down to £1.7 – 2.3bn. We also tried to minimise the new road building either side. We also had the big financial crisis in 2008 so at that point there were a lot of very hungry contractors and we could get a very competitive bid. They all came under so that let us shrink the budget again to £1.4 – 1.6 billion.”

As for delivering the bridge on time, the story is not quite so successful. The original target for completion was December 2016, with a 20 per cent delay built in, and then there was a contractual completion date of June 2017. Both targets were missed, mainly, says Climie, because of the weather.

“That was fundamentally the main cause of the delay,” he says. “No matter how much you plan, a lot of the activities that we do here are weather dependent: the rough water, the strong winds. Stuff is going to happen - technical issues, weather issues - you build in an allowance for that and you know that some or all of those issues are going to happen.”

Climie believes that, for those reasons, the delays on the crossing are forgivable. “You look at it now and we’re going to be opening 10 weeks after the contractual date – now 10 weeks in a six and a half year project is about three per cent. If you were getting some work done on your house and it overran by three per cent, that’s two hours. You get some projects that double the time they were expected to take and the costs escalate as well.”

Climie is very aware, however, that some of the other problems the project experienced are harder to explain, such as the death last year of the construction worker John Cousin. Mr Cousin, who was 62, was directing a crane at the north tower when he was struck and killed and Climie remembers the gut-wrenching feeling when he heard the news.

“A fatality really does turn you upside down and makes you consider: do I want to be doing this?” he says. “It’s a gut wrenching feeling and you never ever want it to happen. And when it does, you feel personally responsible.”

Climie says Mr Cousin's death was particularly upsetting because it involved an everyday construction procedure. “He was one of the fitters down on the yard, and he’d gone out to work on a crane on the deck, just a normal piece of construction plant that just needed some maintenance. I can’t go into the details because there are still inquiries going on but the frustrating part was that when you think of all the technical and complex challenging and to a degree risky things that we do, it was a little bit of routine maintenance that could have been on any site in Scotland and someone ended up being killed.”

I ask Climie, though, if it isn’t inevitable on a massive construction project like the Queensferry Crossing involving 15,000 workers that there will be serious injury and even death. “No, it’s not inevitable,” he says, “If you accept inevitability, then you’re effectively saying that it’s all right for it to happen, and that’s not the case. We emphasised at the start that safety always comes first."

Climie is equally strong on other aspects of the construction that attracted criticism - including the use of the large cylinders or caissons, which some saw as risky in a place like the Firth of Forth. He also says that the fact the bridge is made from 75 per cent Chinese and only 25 per cent British steel was simply a question of timing. There was no facility in the UK that could fabricate the steel in time, he says, and you can tell as he’s saying it, and defending the bridge, that it’s partly because the Queensferry Crossing has become personal for him.

His love for the crossing, and his willingness to defend it, is also because he knows his stuff and his views are built on the solid foundation of an impressive CV. Climie studied civil engineering at Heriot-Watt University, and then worked for the civil engineering company Bechtel. As it happens, he also spent 18 months working on the old Forth Road Bridge in the late 1980s strengthening the supports. At the time, he thought the renovation work meant the bridge would last forever, never thinking that 25 years later he would be back building its replacement.

The experience of building the new crossing has, says Climie, been thoroughly rewarding. There was obviously a possible source of stress in his relationship with the Scottish Government, but Climie says he had a good relationship with the minister in charge, Keith Brown. But was political influence ever an issue - to, say, keep the possible delays quiet? “Never,” says Climie. “Categorically never.” Climie, who is the great-grandson of Robert Climie, who was the Labour MP for Kilmarnock in the 1920s, also says that his own political views were entirely private and it was never been an issue with the SNP government. “It’s never been a conflict and it never would be,” he says. “I’m an engineer and I build bridges and that has nothing to do with politics.”

As far as the future is concerned, the focus for Climie now is on ensuring the bridge is running efficiently. The huge 3.9m high wind shields should mean that the bridge never has to close because of the weather; Climie has also put in place a maintenance programme that will cost an average of £6-7million a year. As part of the bigger picture, that figures is peanuts, he says, and should ensure that the bridge lasts 120 years at the very least.

In the shorter term, Climie and his colleagues face moving out of the bridge HQ and seeing it dismantled completely. Most of the staff will go on to other projects. As for Climie, his contract ends in October and he will take a few months off. It’s all quite bittersweet, he says. But it seems likely that he will be back to work at some point, somewhere in the world. He knows that there will be other bridges.