Speed Limiter

What is a speed limiter? Definition and purpose

The speed limiter is an Advanced Driver Assistance System (ADAS) designed to improve safety and comfort by preventing the vehicle from exceeding a maximum speed previously set by the driver. Easily activated via steering wheel controls or a dedicated stalk, it allows you to set a speed cap (for example, 50 km/h in the city or 130 km/h on the highway). Once activated, the driver can accelerate and decelerate normally as long as they stay below this limit. It is a valuable tool for complying with speed limits, particularly in areas where the authorized speed changes frequently, thereby reducing the risk of fines and, more importantly, accidents.

How does the speed limiter work?

The operation of the speed limiter is both user-friendly and technically integrated into the vehicle's management systems. When the driver activates the system and selects a speed, the onboard computer records this setpoint. If the vehicle approaches this speed under acceleration, the Engine Control Unit (ECU) intervenes. It modulates fuel injection or throttle opening to create a virtual "wall", rendering the accelerator pedal inoperative for exceeding the threshold. The sensation is one of gentle resistance that prevents going faster. However, safety remains the priority: in the event of an urgent need for power (for overtaking or an avoidance maneuver), a hard and sudden press on the accelerator pedal all the way to the floor activates the "kick-down" function, which temporarily suspends the limiter and unleashes the full power of the engine.

Speed Limiter vs. Cruise Control: What's the difference?

It is common to confuse the speed limiter and cruise control, even though their functions are distinct and complementary. Understanding their difference is essential to using them properly.

• The Speed Limiter: It sets a maximum speed not to be exceeded. The driver must constantly press the accelerator to maintain or vary their speed below this ceiling. It is a "passive" safety system ideal in heavy traffic, in the city, or on winding roads.
• Cruise Control: It maintains a constant speed chosen by the driver, without the latter needing to keep their foot on the accelerator. It is an "active" comfort system, perfect for long journeys on highways or expressways with fluid traffic.

In summary, the limiter prevents you from going too fast, while cruise control keeps you from going too slow.

The Evolution: Intelligent Speed Assistance (ISA)

Technology has evolved the speed limiter into a proactive and connected version: Intelligent Speed Assistance (ISA). This advanced system uses a front-facing camera, often the same one used for lane departure warning, to read and recognize speed limit signs. It cross-references this information with GPS navigation system mapping data.

Thanks to this data fusion, the vehicle knows the maximum authorized speed in real time. Depending on the manufacturer's configuration, the system can then either alert the driver and suggest adjusting the limit with a single click, or automatically adjust the limiter's speed. This technology represents a significant leap forward for road safety. As such, the European Union made ISA mandatory on all new vehicle types approved since July 2022 and on all new cars sold starting July 2024. Although this system can be deactivated, it re-activates every time the vehicle is started, underlining its importance in the European "Vision Zero" safety strategy.