Report numberRA-2006-88
TitleVehicle technique for enhancing directional and vehicle stability
SubtitleOverview and effectiveness of technology for enhancing directional and vehicle stability for passenger vehicles.
AuthorsTobias Denys
Published byPolicy Research Centre for Traffic Safety 2002-2006
Number of pages27
Document languageDutch
Partner(s)Vlaamse Instelling voor Technologisch Onderzoek
Work packageOther: Vehicle technology

Loss of directional stability means the loss of optimal contact or grip between the vehicle and the road surface. Vehicle stability relates to the stability of the entire vehicle. A loss of vehicle stability often results in a loss of directional stability.


The loss of directional and vehicle stability can be caused either by the road surface and weather conditions, or by the driving behaviour and driver’s interventions. The road surface can be in a bad condition, be slippery, etc. The weather conditions can be of that nature that they influence the road surface or the characteristics of the tires. Examples of driving behaviour or driver’s interventions that can cause loss of directional and vehicle stability are over and under steer due to inappropriate vehicle speed, braking and accelerating, evasive manoeuvres and load changes due to a sequence of consecutive bends.


A diversity of systems is available that can prevent or diminish the loss of directional and vehicle stability. In the first place we think of appropriate tires, since they form the direct contact between the vehicle and the road surface. In order to prevent hydroplaning in the case of heavy rainfall, the tires need to have sufficiently deep grooves and the drivers need to maintain an appropriate speed. The use of winter tires during the cold season also increases the directional and vehicle stability.


The movements of the tires are transmitted to the bodywork by means of the suspension. If for example the suspension can’t handle the load changes or the road’s bumpiness in a proper manner, the directional and vehicle stability might be compromised. An active or adaptive suspension however adapts its configuration to the road surface and the driving style.


Loss of directional and vehicle stability due to the driving behaviour or driver’s interventions can be prevented or diminished by stability control, four wheel drive and traction control. Stability control intervenes when under or over steer is imminent. Various studies have proven the system’s effectiveness in preventing accidents. In case of accelerating, taking bends, driving on ice, snow, wet leaves and a wet road surface, a vehicle equipped with permanent four wheel drive maintains its directional and vehicle stability during a longer period. When wheels are spinning and as a consequence loosing grip, traction control can intervene by slowing them down.


Loss of directional and vehicle stability due to braking can be prevented by different systems. ABS prevents the wheels from blocking when the brakes are applied in a strong manner, this way the vehicle remains handleable. Electronic brake distribution takes care of an effective distribution of the braking force between the front and the rear axle, taking the weight shift due to the braking manoeuvre into consideration. Emergency braking systems are capable of recognizing an emergency stop and consequently applying the full braking power.


This reports most important recommendation on the short term regards the accelerated and general introduction of vehicle safety systems, in particular stability control. A broad introduction of intelligent vehicle safety systems cannot depend on the private business case only, and needs the support of the public sector. The 2 main mechanisms for the public sector intervention are on the one hand promoting awareness and information, and on the other the introduction of financial incentives for the buyers of vehicles equipped with advanced safety systems.


The European Commission has launched long term proposals for measures to promote the development of intelligent vehicle safety systems, and to remove barriers which prevent their large-scale introduction and take-up in Europe. The proposals are related to: promoting intelligent vehicle safety systems; adapting the regulatory and standardisation provisions; and removing the societal and business obstacles. Also important are a thorough analysis of present and future accident data; developing public sector road maps in close co-operation with the industry; far-reaching standardization; stimulating and supporting road users and fleet owners to buy vehicles with intelligent road safety functions and to use safety-related services by incentives; and executing awareness campaigns. The OECD states that the development of a solid evaluation programme to assess the performance of future safety systems is essential.

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The Policy Research Centre for Traffic Safety carries out policy relevant scientific research under the authority of the Flemish Government. The Centre is the result of a

cooperation between Hasselt University, KU Leuven and VITO, the Flemish Institute for Technological Research.


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