They also said the cost of the scheme had been cut further thanks to savings, by £50 million to £1.325-1.35 billion.
Project director David Climie told MSPs: “We continue on target for opening at the end of 2016.
“When the bridge was first considered in 2007, a ten-year timescale was considered extremely challenging.
“We are absolutely focused on the target of having traffic on the bridge by the end of the year, whatever happens.”
Mr Climie, of the Scottish Government’s Transport Scotland agency, said such factors included more bad weather or any further closures of the Forth Road Bridge.
However, he admitted progress had been hampered by adverse weather during the winter, with the bad outweighing the good.
Mr Climie also highlighted yesterday’s Met Office announcement that Scotland had had its wettest winter since records began 105 years ago.
He said: “We have not made as much progress as we would have liked over the winter, but it [completion by December] is still do-able.”
Mr Climie’s comments to Holyrood’s infrastructure and capital investment committee followed media claims that the bridge opening would be delayed because work on the towers and vehicle deck was behind schedule.
The three towers were completed between October and December, with the centre tower 210m (689m) above water level, making it the UK’s tallest bridge structure.
The towers have also dwarfed those of the adjacent Forth Road Bridge’s towers, which are one quarter lower.
Mr Climie said a total of 43 of the 110 sections of deck had been lifted into place, with the final shipment from China about to arrive.
The latest cost saving means the project budget has been reduced by £245m since construction began in 2011.
The bridge was originally expected to cost £3.2-£4.2bn but this was cut by £1.7bn by axing plans for extra lanes for public transport.
Buses and taxis will now continue to use the Forth Road Bridge when other traffic is switched to the new crossing.
Further savings over the last five years have previously reduced the cost to £1.45-1.6bn and then to £1.4-1.45bn.
Mr Climie said the workforce had peaked at 1,287 in November. He said a dispute which erupted in December over holiday pay was still being resolved by the Forth Crossing Bridge Constructors contractors’ consortium, but it had not affected construction progress.
Mr Climie said the problem had been caused by changes to payment regulations which had left staff receiving less than they had expected.
He said: “This was not very well understood and perhaps not very well communicated.”