NZTA Northland manager Jacqui Hori-Hoult said following the deaths all contractors were asked to review their work with a particular focus on safety.
''This meant that during this time safety across the network was the priority and some activities like rubbish collection were placed on hold until we could assess the safest roadside working conditions,'' she said.
''We have now returned to business as usual and efforts are being made to catch up on the rubbish collection backlog.''
Hori-Hoult said NZTA took the safety of its crews and other road users seriously.
Fulton Hogan, which is contracted by NZTA to maintain Northland's state highways, did not respond to Advocate inquiries.
While state highway maintenance is the responsibility of NZTA, other roads come under local authority jurisdiction.
Far North District Council spokesman Richard Edmondson said removing litter from roadsides was not included in council roading contracts due to the sheer size of the roading network.
However, the council did remove household rubbish or large quantities of rubbish, as opposed to litter thrown from car windows.
Removing illegally dumped rubbish around the district, including from roadsides, cost ratepayers $118,065 in 2017/18.
''Some of our roading contractors voluntarily pick up rubbish during annual clean-up events but they're not contracted to do this,'' he said.
The council's town maintenance contractor Recreational Services also removed litter from selected parks and the main streets of Kaitaia, Kerikeri, Kaikohe and Paihia.
The council supported clean-ups at beaches and reserves by removing the collected rubbish without charge and would do the same for volunteers wishing to remove litter from roadsides.
''However, we encourage them to contact us first so we can discuss traffic management and safety issues,'' Edmondson said.
