The 'NorthConnex' motorway is scheduled to open early in 2019 and will provide a connection from the M1 motorway to the Central Coast and Newcastle to Sydney's M2 motorway.

At a ceremony to mark the start of construction of the $3 billion motorway on Friday, Roads Minister Duncan Gay said measures would be put in place to force trucks not making local deliveries or carrying dangerous goods to use the nine-kilometre tunnel.

"We are putting a timer that would indicate a fair time to get through, and if trucks leave and rejoin they will be picked up by the technology that indicates that they've been deliberately doing a bypass and they will be fined at least the equivalent of the fare," Mr Gay said.

The motorway project, which has been talked about for decades, is being part paid for with $405 million grants from the state and federal governments. Motorway operator Transurban is funding the rest after being granted longer toll concessions on other roads.

Transurban's NSW general manager, Andrew Head, said gantries could be installed at the start and finish of the motorway corridor. They would enable Transurban "to determine whether or not that truck is making a through passage, and therefore should be in the tunnel and not on the local streets.

"If it is providing services to a business on the corridor, it will be exempt," he said.

Mr Gay, however, said a similar system of fining truck operators who did not use the NorthConnex tunnel would not be applied on other toll roads in Sydney, such as the new WestConnex motorway.

"We don't believe this problem will be on Parramatta Road running beside WestConnex,'' he said.

The Pennant Hills road corridor has been identified as the nation's worst, and the new tunnel is estimated to take up to 5000 trucks a day from Pennant Hills Road.

The funding agreement for the motorway was first put in place by the state Coalition government and the former federal Labor government.

At the ceremony on Friday, the Member for Berowra, Philip Ruddock, said: "There is only one point in which the traffic that has to get across Sydney and go north can travel and it's on Pennant Hills Road, and that congestion has been a major impediment to economic development of this city."

The Assistant Minister for Infrastructure, Jamie Briggs, said: "The hotspot of infrastructure across the country is NSW, is Sydney, under the leadership of [Premier] Mike Baird and Duncan Gay."

Labor's roads spokeswoman, Jodi McKay, said she understood the trucking industry had significant concerns about the transparency around the fine regime, and how it would be enforced.