Quick Guide
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Understanding Speed Assistance
Speed assistance technologies are designed to help the driver understand and manage the speed of the vehicle. Depending on the system fitted, they may identify the prevailing speed limit, warn the driver when the vehicle exceeds it or provide assistance in controlling the vehicle's speed.
Managing vehicle speed involves more than simply recognising the legal speed limit. The appropriate speed can also depend upon traffic, visibility, weather and road conditions, while technologies such as cruise control and Adaptive Cruise Control (ACC) can influence how the vehicle maintains or adjusts its speed during a journey.
These technologies can include Traffic Sign Recognition (TSR), Intelligent Speed Assistance (ISA) and speed limiters. Cruise and distance assistance systems perform a different function, but are also relevant to understanding how vehicle speed may be managed. Although these technologies may work together, their capabilities and the level of assistance they provide can vary between vehicles and manufacturers.
Traffic Sign Recognition ('TSR')
Traffic Sign Recognition (or 'TSR') can identify certain road signs and display relevant information to the driver, including information about the prevailing speed limit.
Depending on the system fitted, information may be obtained using a forward-facing camera, digital mapping data or a combination of different sources.
The information recognised by the system can then be displayed within the instrument panel, head-up display or another area visible to the driver.
The ability of a camera-based system to recognise road signs can be affected by poor visibility, weather conditions, obscured or damaged signs and other circumstances that make a sign difficult to identify. Mapping information may also not always reflect temporary or recently changed speed limits.
Traffic Sign Recognition is primarily an information system. The speed limit displayed by the vehicle should not be assumed to replace the driver's responsibility to observe road signs and determine the applicable speed limit.
Intelligent Speed Assistance ('ISA')
Intelligent Speed Assistance (or 'ISA') uses information about the prevailing speed limit together with the speed of the vehicle to help the driver manage vehicle speed.
Depending on the system fitted, ISA may provide a visual or audible warning when the vehicle exceeds the identified speed limit. Some systems may also provide another form of feedback or assistance intended to encourage the driver to reduce speed.
ISA should not be confused with cruise control. Its primary purpose is to assist the driver in recognising and responding to the applicable speed limit rather than maintaining a selected cruising speed or distance from traffic ahead.
The way ISA operates can vary between vehicles. Drivers may therefore experience different types of warnings, feedback or intervention depending on the vehicle, its settings and the particular system fitted.
ISA should not be assumed to determine an appropriate driving speed in every situation. The driver remains responsible for observing the applicable speed limit and adjusting vehicle speed to suit the road, traffic, visibility and weather conditions.
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Speed Limiters
A speed limiter is designed to restrict the speed of a vehicle rather than simply warn the driver that a particular speed has been reached or exceeded.
Some vehicles allow the driver to select a maximum speed, after which the system can restrict further acceleration beyond the selected limit. The way the driver can override, adjust or deactivate a driver-selected limiter will depend on the vehicle and system fitted.
Speed limiting can also have a different meaning for commercial vehicles. Certain goods vehicles may be required to have equipment fitted that restricts their maximum speed, rather than relying upon a limit selected by the driver.
A speed limiter setting should not be assumed to represent either the legal speed limit or an appropriate speed for the conditions. The driver remains responsible for observing the speed limit applying to the vehicle and adjusting speed to suit the road, traffic, visibility and weather conditions.
Vans and UK Speed Limits
Van drivers should be aware that the maximum speed permitted for their vehicle may differ from the speed limit applying to a car using the same road.
The speed limit applying to a van can depend upon factors including the type, classification and weight of the vehicle. Different rules can also apply to car-derived vans and qualifying dual-purpose vehicles.
This distinction is particularly important when considering Traffic Sign Recognition and Intelligent Speed Assistance. A road sign or speed assistance system may identify the general speed limit applying to the road, but this should not be assumed to represent the maximum speed legally permitted for every vehicle using it.
Drivers should therefore understand the speed limits applying to their particular vehicle and should not rely solely upon a speed assistance system to determine the maximum speed at which the vehicle may legally be driven.
Current speed limits for different types of vehicles and roads are available from the UK Government speed limits guide and The Highway Code.
Vehicle Speed and Speedometer Accuracy
Drivers should also be aware that the speed shown on a vehicle's speedometer may not exactly match the vehicle's true road speed.
UK requirements allow a speedometer to indicate a speed higher than the vehicle's true speed within specified tolerances, but it must not indicate a speed lower than the true speed under the applicable test requirements.
This means that the speed displayed by the vehicle, the speed identified by a driver assistance system and the vehicle's actual road speed should not necessarily be assumed to be identical.
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Cruise and Distance Assistance
Cruise and distance assistance systems are designed to help the driver manage vehicle speed and, in more advanced systems, the distance from traffic ahead.
These technologies range from conventional cruise control, which maintains a speed selected by the driver, to Adaptive Cruise Control (ACC), which can also respond to changes in the speed of traffic ahead.
Conventional Cruise Control
Conventional cruise control allows the driver to select a vehicle speed which the system then attempts to maintain without the driver continuously operating the accelerator.
The driver remains responsible for monitoring the road and surrounding traffic and must intervene when the selected speed is no longer appropriate. Conventional cruise control does not normally adjust the vehicle's speed to maintain a distance from traffic ahead.
Adaptive Cruise Control ('ACC')
Adaptive Cruise Control (or 'ACC') adds the ability to monitor traffic ahead and adjust the vehicle's speed to help maintain a selected distance from the vehicle in front.
Depending on the system fitted and the traffic conditions, ACC may reduce the vehicle's speed when approaching slower traffic and increase it again when the road ahead becomes clear, up to the speed selected by the driver.
Some systems can operate over a wide range of speeds and may be capable of slowing the vehicle to a standstill in congested traffic. Depending on the vehicle, the system may also be able to resume following traffic automatically or after an input from the driver.
These capabilities vary considerably between vehicles, and the term Adaptive Cruise Control should not be assumed to describe an identical level of functionality on every car or van.
Intelligent and Predictive Cruise Control
Manufacturers may use terms such as Intelligent Cruise Control, Intelligent Adaptive Cruise Control or Predictive Cruise Control for systems that combine conventional adaptive cruise functions with additional information.
Depending on the system, this information may include recognised speed limits, digital mapping, road layout or navigation data. The vehicle may then use this information to assist with adjusting its speed in response to changing road conditions or speed limits.
Manufacturer terminology varies considerably, so the name given to a system should not by itself be taken as an indication of its precise capabilities.
Understanding the Limitations
Speed, cruise and distance assistance technologies can provide useful information, warnings and assistance, but their capabilities vary between vehicles and manufacturers and depend upon the particular systems fitted.
Information about speed limits, vehicle speed, surrounding traffic and road conditions may be obtained from different sources, including cameras, sensors and mapping data. The information available to a system, and the way in which the vehicle responds to it, may therefore vary according to the technology and driving conditions.
These technologies should not be assumed to determine an appropriate driving speed in every situation. The driver remains responsible for observing the speed limit applying to the vehicle and adjusting speed to suit the road, traffic, visibility and weather conditions.
Speed Assistance and Vehicle Safety Ratings
Speed assistance technologies form part of modern vehicle safety assessment. Euro NCAP considers the performance of systems designed to help drivers recognise and respond to speed limits and manage vehicle speed.
This can include technologies that identify speed limits, provide warnings or feedback to the driver and, depending on the system fitted, provide assistance in controlling vehicle speed.
The presence of a particular Speed Assistance technology does not, by itself, determine a vehicle's overall safety rating. Euro NCAP assesses a range of safety technologies and their performance as part of its wider assessment of the vehicle.
You can explore our Euro NCAP safety ratings for cars and vans using the searchable vehicle safety information below.
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Independent Vehicle Information
DriveSmart provides independent information designed to help motorists, self-employed drivers, businesses and fleet operators understand vehicle ownership.
Our searchable vehicle databases combine technical specifications, taxation, running costs, grants and safety information, allowing users to compare vehicles using consistent, structured data.
Whether you are choosing a family car, an electric company car or a commercial van, our aim is to help you understand the facts before making your decision.
Our Vehicle Safety Hub Is Growing
DriveSmart continues to expand its Vehicle Safety Hub with additional guides covering modern vehicle safety technologies, commercial vehicles, electric vehicles and independent safety information.
As new vehicle assessments become available, our searchable databases and supporting guides will continue to develop.
Important Safety Information
Advanced Driver Assistance Systems are designed to assist the driver. They do not replace the need for the driver to remain attentive, maintain control of the vehicle and respond appropriately to road, traffic and weather conditions.
The availability, operation and limitations of individual ADAS technologies vary between vehicles, manufacturers and vehicle specifications. Drivers should familiarise themselves with the systems fitted to their vehicle and follow the information and instructions provided by the vehicle manufacturer.
No driver assistance system should be relied upon to prevent a collision or to operate correctly in every situation. The driver is still responsible for the safe operation and control of the vehicle at all times.
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Explore Euro NCAP Safety Ratings