Every HGV driver knows the feeling. You're running down the M6 southbound on a clear night, nothing in front, doing 56. The road is empty for three miles. You sit there at 56. Doesn't matter what's ahead — the limiter has you pegged, and it's not moving for anyone.
That wall isn't accidental. It's a legal requirement. And it's more tightly specified than most drivers realise — right down to who can touch the seal and what happens if that seal is broken.
Which regulation and what it says
Speed limiters for goods vehicles are governed by Regulation 36B of the Road Vehicles (Construction and Use) Regulations 1986. The requirement applies to most HGVs you'd be driving day-to-day:
Goods vehicles over 12,000 kg registered from 1 January 1988 must have a speed limiter fitted and set so the stabilised speed of the vehicle cannot exceed 90 km/h. That's approximately 56 mph. Goods vehicles between 3,500 kg and 12,000 kg first used from 1 January 2005 have the same 90 km/h requirement.
There's an older band as well — goods vehicles between 7,500 kg and 12,000 kg first used between 1 August 1992 and 1 January 2005. Those were required to be limited to 60 mph (approximately 97 km/h). The different limit reflects the era of the legislation; the more recent 90 km/h harmonises with EU-wide requirements.
The regulation uses the term "stabilised speed" rather than just "top speed". That means the limiter has to hold the vehicle at 90 km/h during normal driving — not allow a brief overshoot to 92 before correcting. The calibration has to be stable at 90.
The seal requirement
Regulation 36B also says the limiter must be "sealed by an authorised sealer". That's the part most drivers haven't thought about much. An authorised sealer is a DVSA-approved workshop. When the limiter is calibrated or recalibrated, the workshop attaches a tamper-evident plaque or seal to the installation. The plaque carries the workshop details, the calibration date, and the set speed.
The vehicle must carry this plaque, and it must be legible. If it's missing, damaged, or shows signs of tampering, that's a problem — not just an advisory, but a potential major defect that can lead to a PG9 prohibition at roadside.
The logic is straightforward: the seal proves the limiter hasn't been adjusted since calibration by an approved workshop. A broken seal raises the question of whether the limiter is still set correctly. DVSA can't assume it is.
Where the plaque lives
The calibration plaque is usually mounted somewhere visible in the cab — often near the tachograph head or on the fuse panel cover. It'll show the vehicle registration (or VIN), the approved workshop details, and the set speed. Some workshops put it on the bulkhead, some on the dashboard panel, some on the driver's door pillar.
If you're doing a walkaround check on a vehicle you haven't driven before, it's worth knowing where the plaque is on that specific unit. On a Scania R-series it's typically on the fuse box cover. On a DAF XF it tends to be on the nearside dash panel. On a Volvo FH, usually somewhere around the centre console.
Can't find it? That's worth a mention in the defect book. Not a "do not drive" defect necessarily, but a note that the plaque wasn't located — because if you're pulled by DVSA and it's missing, it becomes your problem as much as the operator's.
What a broken or missing seal means at roadside
DVSA inspect speed limiter compliance as part of roadside checks. The officer will check the plaque — is it present, is it legible, does it match the registration, has the seal been tampered with. If it's broken or missing, they have the option to test the vehicle's actual top speed against the 90 km/h requirement. That test happens at the roadside with the officer in the cab or at an adjacent test area.
A speed limiter that tests above 90 km/h is a major defect. PG9 prohibition. Vehicle stopped. Operator notified. The driver gets a fixed penalty, the operator gets an OCRS hit, and the vehicle doesn't move until a compliant limiter is fitted and sealed by an authorised workshop.
A vehicle where the seal is broken but the limiter tests correct is still a problem — DVSA may issue a delayed prohibition (PG10) requiring the seal to be replaced within a specified timeframe. It's not the end of the day, but it goes on the OCRS record.
What the limiter doesn't cover
The 90 km/h limiter is a maximum speed. It doesn't enforce the lower speed limits that apply to HGVs on certain roads. National speed limit on a single carriageway for an HGV is 50 mph (80 km/h). Dual carriageway is 60 mph (97 km/h). Motorway is 70 mph (113 km/h) — but the limiter stops you at 90 km/h (56 mph) regardless, so on a motorway you're limited well below the legal maximum anyway.
The limiter also doesn't protect you from speeding on a lower-limit road. If you're on a 30 mph stretch through a village, the limiter sitting at 90 km/h isn't doing you any favours. You're still responsible for matching the road speed limit. A driver doing 56 mph through a 30 zone because "the limiter didn't stop me" is still getting six points and a ban.
Tampering — don't
I've seen it done. Bypass devices, remapped ECUs, adjusted cables on the old mechanical linkages. It's not clever and it's not safe. Tampering with a speed limiter is a criminal offence under Regulation 36B — specifically, the regulation says the device must be "maintained in good and efficient working order". Intentionally disabling or bypassing it is a straightforward breach.
Beyond the legal side: there's a reason HGVs are limited to 56 mph. The stopping distances at 70 mph are not something a loaded 44-tonne artic handles the same way a car does. The limiter exists for everyone on the road. Bypassing it isn't a technical achievement — it's a decision to put unmanaged weight and momentum on public roads with no ceiling. Not worth it.
At the PMI
Speed limiter compliance is checked during the six-weekly Preventive Maintenance Inspection. The workshop should be confirming the plaque is present and legible, the seal is intact, and the calibration date is current. It's also checked at the annual goods vehicle test.
If the limiter seal has been broken during a repair (some engine work requires accessing the limiter installation), the operator must have it resealed by an authorised workshop before the vehicle returns to service. That applies even if the limiter itself wasn't adjusted — the seal must be intact, and a broken seal without an authorised resealing record is still a defect.
It's one of those checks that runs in the background every inspection and mostly never causes an issue. Until the day someone can't find the plaque at roadside and suddenly it matters a great deal.
Keeping maintenance records current and accessible is easier with a dedicated tool. ShiftOwt tracks compliance dates including PMI cycles — £5.99/mo for drivers, agency pricing on request.