Megaprojects are notorious for eye-watering cost overruns and arduous delays. In fact, over 98% exceed their budget or are delivered late according to consulting firm McKinsey. Still, there are some stunning exceptions to the rule. Raise a glass to 15 major construction jobs that were completed spectacularly under budget and way ahead of the due date.

The rail link that opened up the West and transformed America was completed in 1869, a staggering seven years ahead of schedule. In total, the First Transcontinental Railroad spanned 1,912 miles, connecting the US rail network at Omaha, Nebraska, with the Pacific coast at San Francisco.

The railroad cost $125 million at the time, which was miraculously on budget. That works out around $2.5 billion (£2bn) when adjusted for inflation. However, the final bill was significantly smaller than the amount budgeted.

A wonder of 19th century engineering, Paris' Eiffel Tower was completed in record time. Construction of the wrought-iron icon, which was designed by a trio of architects and delivered by engineer Gustave Eiffel's company, began in January 1887 and ended in March 1889, a seriously impressive feat given the complexity of the job.

Even more impressive is the final bill. The total cost of building the Eiffel Tower came in at a tidy 6% under the initial budget of 8.3 million francs, which is $41.5 million (£33m) in today's money, making for a saving of 500,000 francs or $2.5 million (£2m) when adjusted for inflation.

The Panama Canal remains one of the largest and most challenging megaprojects ever attempted. The fact it was completed by US engineers a year before schedule in 1914 makes the Central American waterway all the more extraordinary.

Adding to the superlatives, the canal cost $23 million less than the $398 million budgeted for the entire job. In today's money, this saving amounts to a beefy $589 million (£468m).

Another American engineering triumph, the Hoover Dam, which was originally known as the Boulder Dam, went operational in 1936, a good two years ahead of the planned date and much to the delight of the Depression-era Hoover administration.

Adding to the delight of the authorities, the dam, which straddles the border of Nevada and Arizona, was $15 million under budget. The entire megaproject cost $49 million – $903 million (£717m) in today's money – and the money saved works out at $276 million (£220m).

Staying in the US, San Francisco's most emblematic bridge opened in May 1937, many months ahead of schedule. At the time, the crossing had the longest suspension bridge span in the world (the record was claimed in 1964 by the Verrazzano-Narrows Bridge in Brooklyn, New York).

Needless to say, the tight efficiency of the construction job resulted in big savings. The bridge cost a total of $35 million – $622 million (£494m) in 2019 dollars – but the final bill was $1.3 million under budget, or $23 million (£18m) when adjusted for inflation.

The world's tallest building from its completion until 1970, Manhattan's Empire State Building was finished four and a half months ahead of schedule. The Art Deco skyscraper took just a year and 44 days to build, and opened its doors in May 1931.

As well as being fast to erect, the Empire State Building was a veritable bargain. The final bill of $40.9 million, which is around $659 million (£524m) when adjusted for inflation, was considerably under budget.

Abandoned projects the US government spent billions of taxpayers' money on

Mozambique's largest ever private sector and direct foreign investment project, the Mozal aluminium smelting facility was up and running in September 2000, a very respectable six months ahead of schedule.

The final bill for the facility was a stellar result too, coming in $100 million under budget at $1.2 billion. The saving in today's money amounts to some $150 million (£119m). Thanks to its successful delivery, Mozal was named project of the year by the International Project Management Institute (PMI).

The first phase of Vancouver's second SkyTrain rapid transit line is a masterclass in how to deliver an urban public transport megaproject. Managed to perfection, the new route from Columbia to Commercial Drive opened ahead of schedule on 7 January 2002.

Wowing its owner and key investor TransLink, the megaproject was a lot more affordable than expected. All in all, the final construction bill was $37 million under budget, around $53 million (£42m) in today's money.

Building the tallest bridge in the world was bound to be fraught with difficulty, but Effiage, the engineering firm in charge of constructing the towering Millau Viaduct in southern France, pulled it off in next to no time.

The crossing was completed in December 2004, three months before the due date. Best of all, the megaproject stayed well within budget, with the final cost working out at a value for money $710 million (£565m) in 2019 dollars.

Heathrow Terminal 5 might have been 20 years in the planning, but when the airport extension finally did get the green light, it was delivered super-speedily. The megaproject was opened by Queen Elizabeth II on 14 March 2008, comfortably ahead of schedule.

The total construction cost of $5 billion – $6 billion (£4.8bn) when adjusted for inflation – was notably less than the figure allocated, cementing the success and value for money of the job.

The construction of the first phase of Delhi's shiny new rapid transit system has been described by experts as "miraculous". The megaproject, which is now regarded as the "jewel in India's mass transportation crown", was completed in 2006, almost three years ahead of time.

The line also stayed well within the budget with the final construction cost a steal at $2.4 billion, about $3.1 billion (£2.5bn) in today's money. The cherry on the cake came in 2011 when the capital's metro rail authority recovered all its costs, two years earlier than expected.

Another rapid transit system that was delivered far ahead of time and enormously under budget, the University Link Extension to Seattle's Sound Transit Light Rail system opened in March 2016, six months earlier than scheduled. 

Budget-busting megaprojects coming soon – or are they?

The Central Link extension, which links Capitol Hill and the University of Washington to downtown Seattle, wasn't just fast to construct, it was refreshingly cheap too. Total costs came in at $200 million (£159m) under budget.

The world's third largest offshore wind generating facility, which is located in the North Sea just off the coast of the Netherlands, was completed in April 2017, well ahead of time, despite a delay during the initial stage of construction.

Gemini Offshore Wind Park has shaped up to be a value for money megaproject to boot. The renewable energy endeavour has cost a total of $4 billion (£3.2bn), which is some way south of the projected figure.

Late global megaprojects that blew the budget

Having stayed well within the budget of $9 billion (£7.2bn), German multinational Siemens delivered its largest ever megaproject in July of last year. The contract to build 12 power plants at various locations in Egypt was completed in a record 27.5 months.

No other company has come close to constructing so many power plants in such a short space of time. The state of the art generating facilities, which have a combined capacity of 14.4 megawatts, are expected to save Egypt billions in electricity costs each year.

The first stage of Sydney Metro, the Aussie city's rapid transit system, has come together like a dream. Not only has the urban rail megaproject been delivered a lot earlier than expected having opened ahead of schedule in May, it's also massively under budget.

Sydney Metro Northwest has finished up costing a cool billion Aussie dollars less than anticipated. This works out at a bumper $685 million (£545m), which makes it the biggest saving in our round-up.

'White elephant' projects that defied the critics