VEHICLE DIMENSIONS.
Updated: 2 days ago
HEIGHTS, WEIGHTS & LOADING
Know what you're driving before you move it
When you start driving HGVs professionally, there are some numbers you need to know about your vehicle.
Not roughly.
Not “it's about that.”
You need to understand the height, width, length and permitted weights of the vehicle or combination you are actually driving.
Changing tractor unit, trailer, body or load can change those numbers.
And some mistakes involving vehicle dimensions and weights can have very serious consequences.
1. KNOW YOUR DIMENSIONS
For a typical HGV driver in Ireland, these are useful maximum dimensions to recognise:
Vehicle / dimension | Maximum |
Motor vehicle | 12.00 m long |
Trailer | 12.00 m long |
Articulated vehicle | 16.50 m overall |
Motor vehicle + one trailer | 18.75 m overall |
Most goods vehicles over 3.5t | 2.55 m wide |
Conditioned/refrigerated vehicle | 2.60 m wide |
Vehicle height* | 4.00 m |
*Other than the separate provision for double-deck large public service vehicles.
These are general maximum dimensions; special vehicles, abnormal loads and particular configurations can be subject to different requirements. RSA
Why does a driver need to know this?
Because you're the person trying to put that vehicle through a gateway, around a corner, along a narrow road and underneath a bridge.
A 16.5 m artic does not follow the same path around a corner as your car.
Your trailer wheels cut in.
The rear of the trailer can swing out.
The unit and trailer need space.
Your mirrors add to the practical width you need to consider.
And the roof of the trailer doesn't magically disappear because your sat-nav told you to go under a bridge.
2. KNOW YOUR HEIGHT
Seriously. KNOW YOUR HEIGHT.
Of all the dimensions in this guide, this deserves particular attention.
Before you move an HGV, know its travelling height.
Not yesterday's vehicle.
Not the trailer you normally pull.
Not what somebody thinks it is.
THE VEHICLE YOU ARE DRIVING TODAY.
Iarnród Éireann specifically tells drivers of high vehicles that they should know the height of their vehicle and load at all times, obey statutory height restrictions and approach bridges cautiously. Irish Rail
Changed trailer?
Check the height.
Changed load?
Check the height.
Carrying machinery, equipment or something projecting above the normal body?
Check the overall loaded height.
Not sure?
STOP AND FIND OUT.
Do not approach a bridge thinking:
“Ah, I'd say we'll fit.”
There are very few good things waiting at the end of that sentence.
3. BRIDGE HEIGHT SIGNS ARE NOT SUGGESTIONS
If a bridge is marked with a height restriction that your vehicle exceeds:
DO NOT PROCEED.
Do not creep underneath to “see”.
Do not rely on another driver having gone through.
Do not assume the sign is overly cautious.
Do not blindly follow the sat-nav.
And do not forget that an arched bridge may have different clearance away from its centre.
Iarnród Éireann specifically warns that clearance at arched railway bridges is available only within the restricted width indicated by the markings or “goal posts”. Irish Rail
HGV SAT-NAV?
Excellent tool.
Still not permission to ignore a road sign.
Even if your HGV sat-nav has your dimensions correctly entered, you must continue to read and obey the signs in front of you.
If the sat-nav says GO and the bridge says NO:
THE BRIDGE WINS.
4. WHAT IF YOU HIT A BRIDGE?
A bridge strike isn't just an embarrassing phone call to the boss.
A strike can:
seriously damage your vehicle or trailer;
damage or dislodge the load;
damage the bridge;
close a road;
stop railway services;
put road and rail users at risk;
cause injury or death;
lead to Garda involvement and prosecution;
have consequences for your driving licence, employment and insurance.
The damage to a railway bridge may also be far more serious than it looks. Following a strike, the structure may have to be assessed before trains can safely use it again. Irish Rail
Could you actually be fined or imprisoned?
Depending on the facts, a collision may result in prosecution under road traffic legislation. It would be wrong to say that hitting a bridge automatically amounts to dangerous driving — the circumstances determine the offence.
But the potential consequences are serious.
Under Irish law, dangerous driving which does not cause death or serious bodily harm can result on summary conviction in a Class A fine, imprisonment for up to six months, or both.
Where dangerous driving causes death or serious bodily harm, conviction on indictment can carry up to 10 years' imprisonment and/or a fine of up to €20,000. Irish Statute Book
If you strike a railway bridge
STOP and report it immediately.
Do not look in the mirror, decide the trailer still appears to be attached and carry on.
Iarnród Éireann's current bridge-height information instructs anyone who strikes or witnesses a railway bridge strike to report it immediately. Its current bridge map gives the emergency reporting number as 01 855 5454. Irish Rail
5. WEIGHT — THERE IS MORE THAN ONE NUMBER
This is where things can initially seem complicated.
They don't need to be.
There are several different weights that matter.
Unladen weight
Broadly, what the vehicle weighs without its load.
Payload
What you can actually carry.
Payload is NOT simply whatever will physically fit in the trailer.
Gross vehicle weight / maximum permitted laden weight
The maximum permitted weight of the loaded vehicle.
Gross combination weight
For a vehicle towing a trailer, there is also a permitted weight for the whole combination.
Axle weight
The amount of that weight being carried through an individual axle or axle group onto the road.
And this last one is extremely important.
6. READ THE PLATE
Don't try to learn every possible weight combination in Irish legislation.
Learn how to read YOUR vehicle.
The vehicle's plate provides the permitted weights applicable to that vehicle, including maximum laden weight and individual axle limits. Current Irish plating requirements specifically provide for “Weights not to be exceeded in the State (IE)”, including vehicle/combination and axle weights. Irish Statute Book
You may see figures for:
Maximum permitted laden weight
Maximum permitted combination weight
Axle 1
Axle 2
Axle 3
…and so on.
These are separate limits.
You don't get to exceed one because you're under another.
7. “BUT I'M UNDER MY GROSS WEIGHT!”
This is one of the most important concepts for a new driver.
Imagine, purely as an easy example, your combination is allowed to weigh:
40 tonnes
You go onto a weighbridge and your total is:
39 tonnes
Happy days?
Not necessarily.
You can be:
UNDER YOUR GROSS WEIGHT
AND
OVERWEIGHT ON AN AXLE.
Why?
Because those 39 tonnes are not necessarily spread evenly across the vehicle.
Imagine carrying something extremely heavy right at the front of the trailer.
Your total weight hasn't changed.
But where that weight is being carried has.
One axle or axle group may now be carrying too much.
Irish regulations specifically require compliance with both the vehicle's permitted laden weight and its permitted axle weights. Irish Statute Book
8. THINK OF IT LIKE SHOPPING BAGS
This is an easy way to understand weight distribution.
You have four heavy shopping bags.
Two in each hand?
Manageable.
Put all four in your right hand?
The total weight of your shopping hasn't changed.
But the weight carried by your right arm certainly has.
Your vehicle is similar.
TOTAL WEIGHT tells you how heavy everything is.
AXLE WEIGHT tells you where that weight is being carried.
Both matter.
9. LOAD POSITION CHANGES AXLE WEIGHTS
Where the load sits matters.
On an artic, moving weight forward can increase the weight imposed through the front of the trailer/tractor.
Moving it rearwards transfers more weight towards the trailer axles.
Exactly how much depends on the combination, axle positions and load.
So don't fall into the trap of thinking:
“It weighs 20 tonnes, and I'm allowed to carry 20 tonnes, so I'm grand.”
You still need those 20 tonnes distributed correctly.
The same principle applies to rigids.
A load concentrated in the wrong place can overload an axle even though the vehicle is within its permitted gross weight.
10. AXLE WEIGHTS
There isn't one magic axle limit for every HGV.
The legal maximum depends on things such as:
whether it is a drive axle;
single, tandem or triaxle configuration;
axle spacing;
tyres;
suspension;
vehicle configuration;
and the limits applicable to the individual vehicle.
For example, Irish regulations generally set 10 tonnes for a single axle, while certain sole driving axles can operate at higher limits subject to specified tyre/suspension conditions.
Tandem and triaxle limits vary according to their configuration and spacing. Irish Statute Book
As a new driver, the important lesson is:
CHECK THE VEHICLE'S PLATE.
If you're unsure what the numbers mean, ask before loading or driving.
Nobody starts professional driving knowing everything.
Guessing is the problem.
11. LIFT AXLES
You may drive a truck or trailer fitted with a lift axle.
When it isn't required, the axle may lift clear of the road.
When required, it lowers and helps carry and distribute the vehicle's weight.
But remember:
When an axle is lifted, it isn't carrying its normal share of the load.
That weight has to go somewhere.
It is transferred to the axles remaining on the road.
So:
LIFTING AN AXLE CHANGES AXLE LOADS.
Modern vehicles may control lift axles automatically depending on load and operating conditions, but the driver should still understand what the system is doing.
Don't override or interfere with axle controls simply because you prefer how the vehicle feels or turns without understanding the consequences.
12. LOAD DISTRIBUTION IS ALSO ABOUT SAFETY
Correct loading isn't only about avoiding an overweight ticket.
Where you put the weight affects how the vehicle behaves.
Poorly positioned or inadequately secured loads can affect:
steering
braking
stability
traction
cornering
axle loading
rollover risk
A badly distributed load can make a perfectly roadworthy vehicle unpleasant — or dangerous — to drive.
13. LOAD SECURITY
If the load can move when you brake, corner or take evasive action, you have a problem.
Different loads require different methods of restraint.
Curtains are not automatically load restraint.
Doors are not an excuse for inadequate load security.
And “it weighs a tonne — it's not going anywhere” is not load securing.
Heavy objects have a considerable amount of energy when a moving vehicle suddenly stops.
Before leaving, ask:
Can it move forwards?
Can it move backwards?
Can it move sideways?
Can it tip?
Can it roll?
Can it fall?
Can anything escape or come loose?
If yes, deal with it before you drive.
14. YOUR VEHICLE HAS CHANGED? START AGAIN.
Yesterday:
Tractor A + Trailer A.
Today:
Tractor A + Trailer B.
Tomorrow:
Tractor B + Trailer B.
Don't assume they're interchangeable.
Check:
HEIGHT
WIDTH
LENGTH
WEIGHT LIMITS
AXLE CONFIGURATION
LOAD
LOAD SECURITY
COUPLING
BRAKES / AIR / ELECTRICS
TYRES
LIGHTS
…and complete your normal walkaround check.
15. HEIGHT CHANGES DESERVE PARTICULAR ATTENTION
A driver who regularly pulls the same trailer can become accustomed to its height.
Then one day somebody says:
“Take that one instead.”
That is precisely when you need to reset your thinking.
Different trailer.
Different height.
Different problem.
And if you regularly swap between fridges, curtainsiders, livestock trailers, double-decks, low-loaders or other specialist equipment, the difference can be considerable.
Put the vehicle height somewhere you can see it.
If the vehicle has an in-cab height indicator/display, use it and make sure it reflects the vehicle you're actually driving.
16. PLAN FOR YOUR VEHICLE — NOT YOUR CAR
Before taking an unfamiliar route, consider:
Low bridges
Weight-restricted bridges/roads
Width restrictions
Tight turns
Narrow roads
Unsuitable town centres
Low branches/overhead structures
Access to the delivery point
Whether there is actually somewhere suitable to turn around
Ireland also has road signs restricting vehicles according to design gross vehicle weight and signs specifying maximum permitted axle loading, so learn to recognise what those signs are telling you. Irish Statute Book
17. DON'T LET SOMEONE ELSE'S CONFIDENCE BECOME YOUR PROBLEM
Someone saying:
“Ah yeah, you'll get her through there.”
doesn't change the dimensions of the lorry.
Neither does:
“We send trucks that way all the time.”
Ask:
What size trucks?
What height?
What weight?
What length?
When was the route last used?
If you're not satisfied, stop and check.
THE FOUR NUMBERS EVERY DRIVER SHOULD THINK ABOUT
Before moving an unfamiliar HGV or combination, you should be able to answer:
↕️ HOW HIGH AM I?
↔️ HOW WIDE AM I?
⟷ HOW LONG AM I?
⚖️ HOW HEAVY AM I — INCLUDING MY AXLES?
If you don't know:
FIND OUT BEFORE YOU MOVE.
And of all of them, burn this one into your brain:
KNOW YOUR HEIGHT.
A wrong turn can be corrected.
A missed junction can be corrected.
A sat-nav can recalculate.
A BRIDGE DOESN'T MOVE!!!!!!!!
For drivers who want to check the official figures rather than relying on social-media graphics or somebody's memory, the RSA weights and dimensions guidance and Iarnród Éireann bridge-height information are excellent resources.
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