There's an immediate problem with the new $1.2 billion, 27km Transmission Gully stretch of motorway out of Wellington, officially opened this morning: mobile blackspots. 

The head of an industry group says the patchy cellphone coverage stems from the limited access that Spark, Vodafone and 2degrees got to the project during its construction and the telco's design plan being ignored - and that he understands the solution will involve smashing up parts of the new motorway. 

"The mobile network operators produced a design plan to provide coverage on Transmission Gully back in 2020," says Paul Brislen, head of the Telecommunications Forum that counts Spark, Vodafone NZ, 2degrees and Chorus among its members. 

"Unfortunately since then, mobile operators have not been able to gain access to the area in order to build any mobile infrastructure prior to the road opening. 

"That means that while there is existing coverage at the terminus ends of the TG road, and some incidental cover along its length, the planned coverage has not been put in place," Brislen told the Herald. 

"There are pockets of coverage at best." 

Anecdotal evidence suggests you can drive for up to three minutes on the new motorway with no cell signal. 

As well as inconveniencing drivers who want to make hands-free calls, or who need mobile data for car audio or navigation systems, the mobile blackspots create a potential emergency calling issue in the event of an accident. 

A stop-gap measure goes part way to filling the breach. 

"In order to help provide cover on the parts of the road between Battle Hill and the Morgans Golf Course, all three operators have deployed a temporary cell site on private land. But that is only a temporary measure," Brislen said. 

"The engineers say they would need to build five towers to provide contiguous coverage as per the design plan. 

"Building new towers now will require access for electricity supply and for the tower construction crews and as I understand it, will involve digging up parts of the new motorway. 

"This is clearly sub-optimal and is another reason why digital infrastructure should be a key consideration in any large-scale infrastructure project." 

The Herald has asked Waka Kotahi NZ Transport Agency, which fielded the telco's recommended mobile network design, for comment. FENZ has also been asked for comment. 

Earlier Ventia - the subcontractor that holds the maintenance contract for the new stretch of motorway - told Stuff it would have full communications along the whole of the new route using its own radio network. 

There was also a network of cameras covering the whole of the new route, and Ventia said it would be able to report any incident to emergency services. 

The over-budget Transmission Gully highway was originally scheduled to open in April 2020. An Official Information Act request by the Herald revealed construction had been plagued by flawed chipseal and water seeping through the road's surface