TRANSPORT MINISTER EAMON Ryan’s remarks that motorists should drive slower to ease fuel consumption have drawn heavy criticism since made yesterday, but experts in the area agree with the Green Party leader.

One has gone further and believes the Government will need to mandate lower speed limits in the coming weeks in a bid to keep costs down – similar to a measure introduced in 1979 in the face of a global oil crisis at the time.

Speaking yesterday as the government announced a cut in the excise duty on petrol and diesel, Ryan said a “practical example” of how people could save costs, would be to drive slower.

“Everyone knows that the speed of cars affects efficiency and if you go above a certain speed, the cost increases dramatically,” he said.

A spokesman for Ryan has indicated that there are currently no plans to change speed limits, saying that the Government’s main response to the increasing cost of fuel is to reduce excise. Details of the cuts were confirmed yesterday after a cabinet meeting. 

“The government is not forcing anyone to slow down, this is merely some helpful advice that could be of help to people who are looking for ways to save extra money on their bills,” the spokesman added.

Sinn Féin frontbench spokesman David Cullinane was among those to blast Ryan’s comments about driving slower.

“As people face into very steep increases in petrol, diesel and home heating prices – the leader of the Green Party Eamon Ryan tells motorists to slow down. God almighty, how more out of touch can you get?”

He added that measures introduced to reduce petrol and diesel costs have already been “wiped out”.

However the stance has received support from experts, who also cite the 1979 measure.

At that time, the general speed limit was reduced as a conservation measure during the energy crisis sparked by the fallout from the Iranian Revolution, as Iran was a key supplier of the world’s oil.

Earlier that decade, the US and the UK introduced their own limits on speed to reduce fuel consumption in response to an oil crisis. 

Dr Paul Deane, from UCC’s Environmental Research Institute, told The Journal that advising motorists to slow down was the correct measure.

“The minister is spot on. It’s quite clear that actually reducing speed limits on how we drive will reduce a potentially massive amount of fuel that we use.

What I would expect the Irish government to start mandating in the next number of weeks – reduced speed limits across motorways in Ireland as this crisis deepens across Ireland and across Europe.

From a policy perspective it’s challenging but from a practical perspective it delivers real significant emissions reductions.

Deane said that reducing speed on motorways from 120km/h to 100km/h could save 15% of the fuel used. “That’s significant,” he added.

Experts from various fields agree that slowing down will lower fuel consumption, although different studies show different savings, depending on the type of car, the direction of prevailing wind and other factors.

Turlough Downes, professor of astrophysics and mathematics at Dublin City University, also highlighted the ”big problem” of air resistance while driving – particularly when hitting the speed limit on a motorway.

He said: “When we go above about 80km/h then the majority of your fuel is being used simply to deal with the drag, simply to deal with the wind resistance.

“There’s some of it still going into dealing with the resistance of the tyre but the main problem is the air resistance.”

For those worried about #FuelPrices for cars: if you drive significant distances then you can *easily* reduce your fuel costs by around 40%. tl;dr speed kills fuel efficiency and driving slower makes a *big* difference /1

— Turlough Downes (@TurloughDownes) March 8, 2022

Professor Downes said the issue is that speed gets “squared” as you drive faster, in a mathematical sense.

“This is why Formula One car crews put so much effort into their aerodynamics.

The big problem with the air resistance is that if you double your speed, your air resistance goes up by a factor of four.

He added: “So it means if I’m driving at 100 kilometres an hour and I increase my speed by 20%, up to 120 kilometres an hour, so it increases by about 40%. And because you’re spending most of your fuel on dealing with the air resistance, it means your fuel goes up by about 40% as well.”

A spokesman for Eamon Ryan told The Journal that the Sustainable Energy Authority of Ireland’s (SEAI) own advice is that motorists who slow down from 120kph to 100kph can save 20-25% of their fuel.