The Government has committed to introducing variable speed limits for the M50.
It was among the measures announced as part of Budget 2021 yesterday.
The move would mean sections of the busy Dublin motorway could be reduced from the current 100km/h speed limit.
On today's Hard Shoulder, the AA's Conor Faughnan explained the idea and how it would work in practice.
He said: "At the moment, motorway speed limits are set by law and by-law - and they're inflexible. They can't vary depending on road conditions or weather.
"The M50 for most of its run it at 100km/h... fixed by law. What this will do is allow them introduce a variable speed - in other words, the speed limit isn't 100km/h, it's whatever it says on the overhead gantry. That might differ from morning to morning, or junction to junction, depending on the road conditions on the M50 itself.
"If you've got a foggy morning they might reduce the speed limit right now.
"If you've got heavy congestion in and around Red Cow, they might drop the speed limit at that location... but leave it at 100km/h for the rest of the motorway."
Mr Faughnan believes the change is a good idea, and should be rolled out across other Irish motorways as well.
However, he cautioned that it might not be a magic bullet to fix congestion issues on the busy M50.
He said: "It's possible that it's a useful tool when used well... it's also possible that used badly it could cause problems, but you'd hope that does not happen.
"I'd be reluctant to make a huge big promise about this, in terms of what it's going to deliver for us in terms of congestion management.
"I think at best it's a decent tool that might be helpful... I wouldn't make a huge boast about it beyond that. When it comes to variable motorway speed limits, I'm actually more convinced by the safety argument: it's a foggy morning in Kildare, so drop the N4 way down."
'Waste of money'
Shane O’Donoghue, editor of CompleteCar.ie, believes the M50 move will be a 'huge waste of money' that will take tens of millions of euro to get working.
He said: "Getting it working properly is another major challenge.
"There have been loads of studies done on this in various parts of the world - some of them are very successful for sure.
"Most of the ones where it works well are motorways where there's more distance between the junctions, and where the motorway is longer."
Mr O'Donohgue said most of the junctions on the M50 are very close together, so there's less room to change speed limits and communicate the fact to people.
However, he suggested: "On the motorways out of Dublin, and the longer motorways further down the country, it could well have a good safety implication to it.
"In terms of congestion, I don't think there's a big enough distance between the junctions... and I just don't think it would have any effect."
