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From speed limits to diamond symbols - your Motorway FAQs answered From speed limits to diamond symbols - your Motorway FAQs answered


From speed limits to diamond symbols - your Motorway FAQs answered

Published 6th September 2021Read Time 31 min

Your Motorway FAQs Answered

Do you know what the numbers at the side of the motorway are or what the little diamonds along the M50 are about? Ireland’s motorway network has come a long way since the first stretch of the M7 opened in Naas in 1983, but it’s growing and changing all the time, with the addition of emergency diversion routes, average speed cameras and, soon, variable speed limits. 

Motorways are among the safest types of roads, but they have their own rules, terminology and signs. They’re also the subject of some enduring myths (such as the existence of a fast lane…). 

Here are the answers to some common motorway questions.

What lane should you drive in on a three-lane motorway?

Forget about “fast lanes” and “slow lanes”- they don’t exist! The golden rule for all motorways in Ireland is “keep left unless overtaking”. So whether it’s a two-lane or three-lane motorway, you should drive in the left lane unless you’re passing slower traffic or moving over to give another driver space to merge at a junction. Then, when it’s safe to do so, you move back left. Essentially, you should not drive in the right lane if the middle lane is empty, and you shouldn’t be in the middle lane if the left lane is open. Remember that you should never undertake – pass someone in the left lane – unless traffic is moving in slow queues and your lane moves faster. 

HGVs, vehicles towing trailers and buses designed for carrying standing passengers should not drive in the right lane of any motorway. They may only use the right lane to get by if an incident obstructs the other lane(s). We have a complete guide to motorway driving rules here.

What’s an auxiliary lane on a motorway?

Is it different from a hard shoulder?

An auxiliary lane is an extra lane to the left of the main lanes that joins an on-ramp with the next off-ramp. It has a closer-spaced broken white line and gives drivers more space to merge. This doesn’t count as the left lane, so don’t enter it unless you plan to exit at the next junction. 

The hard shoulder is the space to the left of the motorway marked off by a yellow line. This is not a driving lane and should only be used when directed by the emergency services or when your vehicle has broken down. Never pull into the hard shoulder for any other reason – it’s one of the most dangerous places to stop, so wait for a layby. (See here for how to stay safe with a motorway breakdown) 

What do the signs on the M50 mean?

Graphic showing the 8 possible diversion symbols


The little yellow signs with black symbols on them on the M50 and nearby routes are emergency diversion signs. If a stretch of the motorway is closed due to an incident, take a note of the shape that appears on the off-ramp or on the electronic signs overhead as you divert. The same shape will appear on road signs on nearby roads, leading you to the next junction where you can rejoin the motorway.

There are 8 different shapes – filled in and outline versions of a diamond, a circle, a triangle and a square – so it’s important to remember the one you are following.

What do the numbers along the side of a motorway mean and what are the phones for?

Along the side of all Irish motorways, you’ll see small signs – sometimes blue rectangles, sometimes little rectangular stakes – with a number and direction on them. They are placed at every 500m and are specific location markers. So, for example, N 35.5 means you are 35.5 kilometres from the start/end of the motorway on the northbound side. These are useful for emergency services – if you ever need assistance, you can use these to give a precise location.

The phones are placed every 1.6 kilometres along the hard shoulder, and give you a direct connection to the TII motorway control centre in case of an emergency. If you can call on your mobile phone, you can also dial them 0818 715 100.

What is the speed limit on a motorway?

The ordinary speed limit for motorways in Ireland is 120km/h, unless otherwise shown in signs. Most of Dublin’s M50 has a limit of 100km/h, with a limit of 80km/h within the Dublin Port Tunnel. The speed limit can also be reduced due to roadworks. 

Bear in mind, too, that some vehicles are subject to lower limits: HGVs are limited to 90km/h, buses to 100km/h and vehicles towing trailers to 80km/h. As stated above, most of these are not permitted to use the right lane, except in exceptional circumstances where the inner lanes are blocked by an obstruction. 

What’s an average speed camera, and where are they in place?

Average speed cameras are permanent speed cameras installed at two points on a motorway that monitor the average speed of motorists by how long it takes them to get to the second camera. They are currently used in the Dublin Port Tunnel (limit of 80km/h). If a driver reaches the second point too soon, a record of the speed violation is auto-generated and sent to the Gardaí, where it’s treated the same way as a speed van image. 

There is also a pilot run of average speed cameras on the M7 in Tipperary, between J26 Nenagh West and J27 Birdhill (limit of 120km/h).  


What does a variable speed limit mean on a motorway?

Updated 17/10/2023

A variable speed limit means the speed limit of the motorway, or even of an individual lane, can be changed depending on the road conditions and traffic congestion. The speed limit can be reduced when there is an incident, heavy traffic or bad weather. The new speed limit is displayed on electronic overhead signs, and that remains active until you pass another sign with a different limit or until the signs are switched off. 
The first roll-out of these in Ireland began on the M50 in Dublin in early October 2021. The first set of signs was switched on the northbound side between J6 Blanchardstown and J4 Ballymun on Monday 4th Oct, as of 12 May 2022, variable speed limits extend from Junction 4 Ballymun to Junction 9 Red Cow on the M50. We have a full round-up on the M50 variable speed limit programme here. 

What vehicles and drivers are allowed and prohibited on Irish motorways?

To be driven on a motorway, vehicles must have an engine over 50cc, be capable of speeds over 50km/h and use inflatable tyres. Tractors that can travel more than 50k/h are allowed. 

Learner drivers (or drivers on a learner permit for the category of vehicle they are driving) are not permitted to drive on motorways. You should never enter a motorway while walking, cycling, or moving animals, including horse-drawn carts. 

What’s the difference between M- and N-roads?

Irish roads are generally named with a letter and a number. An M means motorway (M50, M1, M18, M20, etc), while an N means National Route. There are two types of National Route – primary and secondary – which are both designated N. The lower N-numbers are primary routes, while numbers higher than 51 are secondary routes. 

Some of these National Primary Routes can look remarkably like motorways and lead onto them, including the N4 and N7 on the Dublin/Kildare bounds, the N40 South Ring Rd in Cork, and parts of the N18 in Limerick. These stretches have two or three lanes, but the motorway-specific restrictions generally do not apply, including the restrictions on certain types of vehicles and road users. 

A learner driver, for example, can drive on the N7 but must exit before it becomes a motorway at J9 Naas North. A blue “Motorway Ahead” sign is always placed before a motorway starts so you can choose another route and exit in advance. Always follow signage, keep to the posted speed limit, and remember the “keep-left-unless-overtaking” rule applies on dual carriageways, too. 

Which motorways in Ireland are tolled, and where are the toll plazas?

There are 12 toll locations on Irish roads, most of which are on motorways. They are: 

  • On the M1 in Meath between J7 Julianstown and J8 Duleek 
  • On the M3 in Meath between J5 Dunboyne and J6 Dunshaughlin 
  • On the M3 in Meath between J9 Navan North and J10 Kells 
  • On the M4 on the Kildare/Meath bounds, between J8 Kilcock and J9 Enfield 
  • On the M6 in Galway between J15 Ballinasloe West and J16 Loughrea 
  • On the M7 in Laois between J18 Portlaoise West and the M8 jct 
  • On the M8 in Cork between J16 Rathcormac and J17 Watergrasshill 
  • On the N25 Waterford City Bypass, near where it meets the M9 at Grannagh 
  • On the M50 in Dublin between J6 Blanchardstown and J7 Lucan – this one is barrier-free 
  • At the Port Tunnel in Dublin 
  • At Tom Clarke Bridge in Dublin city centre (East-Link) 
  • At the Limerick Tunnel (on the N18 between J2 Dock Rd and J3 Cratloe) 

A photo of the M50 toll-free signs

How do you pay the motorway tolls?

Can you pay by card?

The price depends on the route, vehicle type and sometimes the time of day. You can find the current charges here. If you’re a frequent motorway driver, you can get various toll tags for your car that allows you to drive through without barriers and have the toll charged to your online account. Some tolls also have multi-trip cards for commuters who travel the same route regularly.

Otherwise, you will need to have pay on the spot, except on the M50. The M50 is barrier-free, so you will need to remember to pay online or at some retailers by 8pm the next day.

All other tolls accept cash but vary when it comes to card payments.

  • No card payments: M8, Limerick Tunnel (N18), Tom Clarke Bridge (East Link)
  • Contactless card payment, but not PIN/Swipe: both M3 tolls, M4
  • Mastercard and Visa cards generally accepted: M1, M6, M7, Port Tunnel, N25

Our Guide to Tolls and Tolling in Ireland  explains costs and everything else you’d ever need to know.

What’s that bit of motorway near the Port Tunnel and Coolock called?

Believe it or not, that stretch of motorway from the M1/M50 interchange down to the Port Tunnel is part of the M50. A common misconception is that it’s the start of the M1 because you can indeed continue straight onto the M1 from there. 

However, it’s actually the start of the M50 – J1 is the Port Tunnel, J2 is Santry and Coolock Lane, and J3 is the M1/M50 interchange. The M1 officially starts at the M50 interchange (J1). 

AA Membership covers you in any car, including if you break down on a motorway. Our patrols fix 8 out of 10 cars at the roadside so you can continue on your way. Sign up online here. 

This is part of a series of driving and road safety blogs. Click here for more driving advice, including driving in all weather, how to deal with vehicle fires, how to prevent rodents from damaging your vehicle, and more.