What Is a Speed Limiter? How Speed Restrictors Normally Work

A speed limiter is a device that stops a vehicle accelerating beyond a pre-set maximum speed, however hard the driver presses the accelerator. Also known as a speed restrictor or speed limit device, it works by controlling the throttle signal (or, on older vehicles, the throttle cable) once the vehicle reaches its set speed. In the UK, speed limiters are a legal requirement on goods vehicles over 3.5 tonnes (56mph) and on buses and coaches (62mph), and many van and car fleets fit them voluntarily.

This guide explains how a speed limiter device works, the main types, when one is mandatory and what installation involves. AutoKontrol has designed and manufactured speed limiters in Chorley, Lancashire, since 1985.

Speed Limiter, Speed Restrictor or Speed Limit Device?

These terms all describe the same thing: a device that caps a vehicle’s top speed.

• Speed limiter (sometimes written “speedlimiter”) is the most common term.
• Speed restrictor is widely used by UK fleets, drivers and enforcement staff.
• Speed limit device is how many people search for it. The formal term in UN ECE Regulation 89 type-approval is “speed limitation device” (SLD).
• Speed governor is another older name you may come across.

Whichever term you use, the technology and the compliance rules are the same. For a UK fleet perspective on the terminology, see our speed restrictor guide for UK fleets.

How Does a Speed Limiter Work?

A modern electronic speed limiter sits between the accelerator pedal and the engine management system:

1. Speed monitoring: the limiter reads road speed from the vehicle speed sensor (VSS) or from the vehicle’s CAN bus network.
2. Threshold detection: as the vehicle approaches the set speed (for example 56mph on a UK HGV), the limiter starts to act.
3. Throttle control: it progressively reduces the throttle demand sent to the engine, so the vehicle stops accelerating.
4. Continuous regulation: while the driver holds the pedal down, the vehicle is held at the set speed. Below that speed, the vehicle drives normally.

The driver feels a smooth levelling off rather than an abrupt cut. A mechanical speed limiter does the same job by physically limiting throttle cable travel. Because a speed limiter controls engine power rather than the brakes, a vehicle can still gain some speed on a steep downhill gradient, so drivers remain responsible for braking. For the technical detail, read how a speed limiter works.

Types of Speed Limiter Device

The right speed limiter depends mainly on how the vehicle’s throttle works and whether you need fixed or location-based speed control.

Type	How it limits speed	Typical vehicles	AutoKontrol product
Electronic (Drive-By-Wire)	Modifies the electronic accelerator pedal signal	HGVs, buses and vans with electronic throttle	DBW speed limiter
Electronic (SENT)	Modifies the digital SENT throttle sensor signal	Latest-generation trucks and vans	SENT Speed Limiter
Mechanical (fuel line)	Works on the vehicle’s fuel line	Older vehicles with mechanically controlled engines, plant	System 80
GPS geofenced	Changes the maximum speed by location	Depots, sites, school and 20mph zones	GeoKontrol 2
Combined limiter and tracking	Speed limiter plus GNSS fleet tracking	Fleets needing compliance and visibility	TrackSpeed

Our guide to the types of speed limiters compares each option in more depth.

What Is an Electronic Speed Limiter?

An electronic speed limiter controls speed digitally rather than mechanically, and it is now the standard for commercial vehicles with electronic throttles. AutoKontrol’s DBW speed limiter is accurate to +/- 1 km/h, works on 12V and 24V systems, is sealed against tampering and is EU/ECE R89 type-approved.

Do not confuse a fitted speed limiter with Intelligent Speed Assistance (ISA) on new cars. ISA warns the driver about the local speed limit and can be overridden, whereas a sealed commercial speed limiter enforces a fixed maximum. If you are researching a car rather than a commercial vehicle, see our guide to car speed limiters.

Are Speed Limiters Mandatory in the UK?

Yes, for certain vehicles:

• Goods vehicles over 3.5 tonnes must have a speed limiter set to 56mph (90 km/h).
• Buses, coaches and minibuses with more than 8 passenger seats must have a speed limiter set to 62mph (100 km/h).

The requirements were introduced in stages from 1992 and are enforced by the DVSA. Some older vehicles are exempt depending on their registration date. Operating an in-scope vehicle without a working limiter can lead to prohibition notices, fines and referral to the Traffic Commissioner.

For vans under 3.5 tonnes and cars, fitting a speed limiter is voluntary. New cars may have ISA, but that is an overridable assistance system rather than a hard limiter. Our guide to mandatory speed limiters in the UK explains the law for cars, vans and heavy vehicles.

How to Install a Speed Limiter

To install a speed limiter correctly:

1. Identify the throttle type. Cable, electronic or SENT throttles each need a different product, so a vehicle survey or compatibility check comes first.
2. Use a trained installer. The limiter is fitted, set to the required speed and road tested.
3. Seal and certify. The unit is sealed with a tamper-evident seal and the installer issues a speed limiter certificate recording the set speed and seal number, which operators of in-scope vehicles need for compliance checks.

Typical fitting times are around 60 minutes for both a mechanical System 80 and TrackSpeed. AutoKontrol installs across the UK through SGH Connect, Scorpion Group’s nationwide installer network. See our speed limiter installation page for coverage, or compare suppliers with our aftermarket speed limiter buyer’s guide.

Benefits of Speed Limiters

• Safety: speed is a factor in approximately 24% of fatal road accidents in the UK (Department for Transport data), and limiting top speed also reduces stopping distances and impact energy.
• Fuel: lower top speeds reduce fuel use. Typical savings are in the region of 10-15%, depending on vehicle type and how much the top speed is reduced.
• Insurance: many fleet insurers offer premium reductions for vehicles fitted with approved speed limiters.
• Compliance: for HGVs and PSVs, a working, type-approved limiter is essential for passing DVSA checks and protecting your operator licence.
• Wear and emissions: lower speeds mean less stress on tyres, brakes and engines, and lower CO2 emissions in line with fuel savings.

Read the full breakdown of speed limiter benefits.

The Road Speed Limiter Market

Demand for road speed limiters comes from three main directions. First, long-standing legal requirements for heavy goods vehicles and buses in the UK and Europe, along with speed limiter regulations in other markets such as the Gulf states. Second, safety technology on new vehicles, including ISA on new cars sold in the EU. Third, fleet operators fitting limiters voluntarily for duty of care, fuel and carbon reporting.

The technology is also shifting. Mechanical limiters remain relevant for cable-throttle vehicles, but electronic Drive-By-Wire and SENT limiters now cover most modern commercial vehicles, while GPS-based systems and combined limiter and tracking devices add location-based control and reporting.

Why Choose AutoKontrol?

• UK designed and manufactured in Chorley, Lancashire, since 1985
• EU/ECE R89 type-approved products, with UTAC, TUV and VCA certification
• A full range covering mechanical, Drive-By-Wire, SENT, GPS geofenced and combined limiter and tracking systems
• TrackSpeed, a combined speed limiter and ScorpionTrack Fleet GPS tracking device available exclusively from AutoKontrol
• Nationwide installation through SGH Connect, part of Scorpion Group

Ready to specify speed limiters for your fleet? Get a free quote or view our product range.

Frequently Asked Questions

What is a speed limiter in simple terms?

A speed limiter is a device that sets a maximum speed a vehicle cannot accelerate beyond. When the vehicle reaches that speed, the limiter reduces the throttle so the vehicle stops accelerating, even if the driver keeps pressing the pedal. It is fitted by law to HGVs and buses in the UK and voluntarily to many vans and cars.

Is a speed restrictor the same as a speed limiter?

Yes. Speed restrictor, speed limiter, speedlimiter and speed limit device are different names for the same technology. Type-approval legislation uses the term “speed limitation device” (SLD), but the function and compliance rules are identical whichever name is used.

Can a driver override a speed limiter?

A type-approved commercial speed limiter is sealed and cannot be overridden from the driver’s seat. Interfering with a limiter that is legally required can result in prohibition notices, fines and operator licence action. This is different from ISA on new cars, which the driver can override or switch off.

Are speed limiters mandatory in the UK?

Speed limiters are mandatory in the UK for goods vehicles over 3.5 tonnes (set to 56mph) and for buses and coaches with more than 8 passenger seats (set to 62mph), subject to some exemptions for older vehicles. They are not legally required on cars or vans under 3.5 tonnes, although many fleets fit them voluntarily.

How long does it take to install a speed limiter?

Installation time depends on the product and vehicle. A mechanical System 80 typically takes around 60 minutes, SENT and GeoKontrol 2 installations around 90 to 120 minutes, and TrackSpeed around 60 minutes, even though it includes GPS tracking.

How much does a speed limiter cost?

The cost of a speed limiter depends on the product, vehicle type and fleet size. Standalone speed limiters have no ongoing subscription, while TrackSpeed includes a monthly fee for the tracking platform. Request a quote from AutoKontrol for pricing tailored to your vehicles.