It comes just months after the state government announced it would spend $12 million installing barriers along the Midland Highway between Ballarat and Creswick, which has been the site of 19 serious crashes in five years.

Four CFA captains of country brigades in Victoria's north-west and north-east say that a multi-million dollar Andrews government strategy to install flexible wire rope barriers along country roads is forcing firefighters to take life-threatening risks to carry out their duties.

VicRoads has admitted it will now have to "retrofit" barriers along parts of the Calder Freeway – costing about $2 million to install per kilometre on complex roads – due to a lack of emergency service access. 

The barriers, which consist of highly-tensioned wire rope supported by steel posts, are designed to avoid head-on and run-off crashes. They will be installed along 20 high-risk rural roads and median strips by the end of 2019, at the cost of $450 million, as part of a $1 billion road safety package.

Firefighters and emergency service controllers support the need for the barriers, but say a lack of consultation with first-responders has resulted in serious oversights in its design. 

For instance, VicRoads' Safe System Road Infrastructure Program director Bryan Sherritt​ said there must be a break in the barriers every 500 metres to one kilometre, to allow for emergency service access.  

But Mr Sherritt admitted that in some areas the breaks were less frequent. 

This has forced emergency services to travel extra kilometres before reaching their destination, significantly increasing response times.

In some cases, fire crews have risked their lives by driving into oncoming traffic to access the closest opening.

"We could be delayed up to five minutes," said CFA Elphinstone captain Andy Chapman.

"That's a long time if you have someone in a car getting burnt ... it's too long."

Mr Chapman warned that if a grass fire breaks out along a highway, motorists will have "nowhere to go".

"The barriers reduce the space in which they can move," he said.

Internal reviews of six crashes over the past six months along the Calder Freeway between Faraday and Malmsbury have found that Mr Chapman's crew was severely hampered by the wire barriers on every occasion. 

In August, firefighters travelled 200 metres in the wrong direction to access a burning car off the Calder, near Elphinstone, to avoid a five-kilometre detour. 

Previously, his crew would have used the median strip to cross the highway and safely park their vehicles, but a recent decision to install a barrier along both sides of the median in some sections, instead of one down the centre, has blocked access.

VicRoads' guidelines stipulate that safety barriers should ideally be installed four metres from the traffic lane to allow vehicles to stop clear of traffic. But they are being installed closer in some areas, leaving insufficient space for fire trucks to safely park.

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Andrew Wilson, captain of the Harcourt Valley brigade, said his crew's response time to a median strip grass fire south-east of Bendigo in mid-November was delayed due to the the barriers cutting off access.

Anthony White, SES controller in Sunbury, said seven-metre trucks cannot do U-turns on narrower roads with ropes on either side, or cross over the median strip in emergencies.

Josh Gamble, captain of the Kyneton brigade, said his crew's response times to a car entrapment one month ago and a grass fire mid-year were delayed, due to a lack of barrier openings.

Max Cox, a retired CFA volunteer of 65 years, after serving as Euroa group officer, said the wire ropes hindered firefighter access to a grass fire on the Hume Highway.

Experienced traffic engineer and former Planning Panels member Des Grogan warned that wire ropes were being installed too close to carriageways, in a letter sent to VicRoads and Minister for Roads and Road Safety Luke Donnellan one month ago.

But Mr Sherritt said research showed that having the barriers closer to the carriageway stopped vehicles from rolling over. 

VicRoads consulted with the CFA, Mr Sherritt said. "We have worked with stakeholders, you pick up things, you learn things, you change it as you go through.

"The work on the Calder is not lost, but we might need to go back and retrofit a couple of things."

Acting Minister for Roads and Road Safety Philip Dalidakis said evidence showed that the barriers reduced the risk of head-on and run-off-road crashes by 85 per cent.

"Dozens of people" hit barriers across Victoria this year, with the barriers "almost certainly preventing deaths and serious injuries" in many cases, Mr Dalidakis said.

Since their installation, wire ropes along the Hume Highway have been hit 65 times, 44 on the Princes Highway and 26 on the Calder Freeway.

Nationals MP Steph Ryan said CFA volunteers in her Euroa electorate warned that rope barriers would "make fighting a fast-moving grass fire on the Hume Highway more difficult".