In some cases, security guards have had to be brought in to protect workers when the abuse has become too dangerous.
The transport agency said there has been more than 10 reports of gun-related incidents against contractors so far this year - compared to four last year.
In the past six weeks workers have been threatened at gunpoint, shot at with BB guns, and had a knife pulled on them in separate events in the North Island.
Warren Epapara, a traffic management supervisor in the Bay of Plenty, said he was shot with a BB gun by a passing vehicle in early November at a worksite in Te Ngae Rd, Rotorua.
“The first thing that came to my mind was why… just a big question mark aye.
“I mean, it’s a work site - you’re travelling through a work site - of course there’s going to be a temporary speed limit. Why would you feel the need to shoot at the truck or the driver of the truck because they’re not doing the speed that you want to go through.”
He's been working in traffic management for the past four years and said the threatening behaviour has increased to become a daily part of the job.
“If it’s not verbal abuse it’s the body language in their cars - it’s like the speeding through site and trying to get as close as they can to you, we get that a lot. It’s just angry people behind the wheel.”
In 2013, George Taiaroa was shot and killed in Waikato while operating stop-go roadworks on Tram Rd in Ātiamuri. Quinton Winders was convicted of his murder in 2016.
This year, the issue came to light again in the aftermath of Cyclone Gabrielle - when road workers reportedly had a pistol and sawn-off shotgun pointed at them at a Hawke's Bay roadblock.
In October, a security guard protecting equipment at Mangahauini River on Statet Highway 35 just north of Tokomaru Bay on the East Coast was threatened at gunpoint - so two extra security guards had to be brought in.
Waka Kotahi’s Mark Owen said while gun incidents are at an extreme end - general abuse against workers has also increased by 20 per cent each year since 2020.
When the abuse gets too dangerous, it can lead to the work site being shut down – causing further traffic delays.
He urged the minority of drivers causing problems to be more respectful.
“It may be a hand gesture, being spat on, objects thrown at them – it’s really endangering their lives, not to say they are working in a challenging environment anyway with the amount of traffic they are working adjacent to."
First Union organiser Justin Wallace said workers were on high alert for verbal abuse in Auckland when operating stop/go signs or diverting traffic in busy areas.
“They know there’s a potential that something could go down because of the high volumes of traffic that is going through.
“There’s thousands of vehicles going through there at any time – sooner or later someone’s going to want to vent their spleen because they’re not happy with the way things are,” Wallace said.
Threats involving weapons need to stop, he said.
“The last thing I want to see is a worker going to work and not going home that shift because obviously something has happened within their workplace which meant they no longer go home to their family.”
Police said they are aware of instances across the country where road workers have faced violence or been threatened.
“It’s unacceptable for road users to use or threaten violence against workers whose job is to keep us all safe," a spokesperson said.
“Police will investigate complaints where road workers, or anyone, has been threatened.”
