What are the new variable speed limits on the M50? AA Ireland

A screengrab from the TII explainer video, showing what the new signs will look like under the existing signage at J5 Finglas.
Image: TII, from M50 Digital Signs Video 01
Updated 4/10/21

What’s changing on the M50? What does variable speed limits mean?


The M50’s new dynamic traffic management system is being rolled out from October 2021, as part of the eMOS programme (Enhancing Motorway Operation Services).

As a driver, the main thing you’ll see are a new set of overhead digital signs for variable speed limits – this means that operators can change the speed limit or manage lane closures.

The M50’s usual speed limit is 100km/h (and 120km/h south of J14 Sandyford). Under this new system, the speed limit can be temporarily reduced for specific stretches when the conditions require it. So, when there are adverse road conditions, like hail or heavy rain, the speed limit can be reduced to a lower one to slow traffic and reduce the risk of collisions. The limit can also be lowered when there is an incident ahead affecting traffic flow, or when the motorway is particularly congested.

The lower limit will apply until the signs show a return to 100km/h or 120km/h. When the digital signs are switched off, the normal limit applies.

Why will this reduced speed limit help traffic on the M50?

Traffic moves best when it flows at a steady speed, rather than speeding up whenever there is a gap and slowing down at congestion.

When something happens to slow traffic, whether an incident or a last-minute manoeuvre by a driver, it can lead to a “shockwave” of braking by all the traffic coming behind it. This causes congestion for far longer than the original incident caused, and can lead to further collisions as drivers hit the brakes. The idea of lowering the speed limit is to prevent this – if traffic is moving more slowly to begin with, there’s less of an impact on braking. The M50 had 1,200 incidents in 2019, 525 of which were collisions.

In bad weather, the road conditions can change quite suddenly and it takes longer to stop – up to twice as long on a wet road, and up to ten times as long on an icy one. Going at a slower speed reduces the risk and makes it easier to control your vehicle.

At the scene of a collision, passing by at a lower speed will also help to keep emergency service workers and the people involved safer.

When do the variable speed limits start?

The system is being installed on a phased basis. The first signs are due to be switched on at 11am on Monday 4th October on the northbound stretch between J4 Ballymun and J6 Blanchardstown. They’re expected to run between 7am and 7pm for the first couple of weeks, and then the southbound side will be switched on after that.

The next stretch, from J6 Blanchardstown to J9 Red Cow is due in the spring, and all stretches should be operational by early 2023.

Who controls the variable speed limits?

The speed limits will be controlled from TII‘s motorway operations control centre with a new Intelligent Transport System. The control centre is based at the Port Tunnel on East Wall Rd, where operators monitor the M50 24/7 by CCTV.

For more information on the system and what the signs will look like, see this video from TII. If you have other questions about motorway driving, including the little “shape” signs on the M50, check out our Motorway FAQs.