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Intelligent Speed Assistance (ISA)

Board resolution taken on 06th November 2018 based on the recommendation the Executive Committee Vehicle Engineering

German Road Safety Council - 2018


Excessive and above all inappropriate speeds are the essential causes of road accidents throughout Europe. Driver assistance systems to assist drivers in their choice of speed have been the subject of discussion for a long time. They have developed from systems which cannot be bypassed by the driver to the assistance systems which can be bypassed, as now proposed in the General Safety Regulation (GSR). Investigations have shown that intervening systems are the most effective systems with regard to accidents, but would have considerably less acceptance by users1.

Accident figures: accident database of the German insurers (UDB)

Evaluation of the UDB clearly shows that inappropriate speed is stated by the police as a considerably more frequent cause of accidents than exceeding the maximum speed limit. This applies for all types of road users. The data in the following table takes into account "speed" as the cause of accidents as it is recorded by the police.

Accident Causes VUA [accident recording] (01-69) Responsible for accident
Car/van Goods vehicle Bus
n % n % n %
3941 100 884 100 334 100
Exceeding the maximum permissible speed 40 1.0 21 2.4 1 0.3
Inappropriate speed in other cases 502 12.7 121 13.7 48 14.4

Source: UDB (accident database of German insurers), motor vehicle liability damage with claims of at least € 15,000 and personal injury

In-depth analysis shows that for the accident cause "inappropriate speed" for cars, trucks as well as buses, increased effectiveness of ISA systems can mainly be expected outside built-up areas and on motorways. For "exceeding the permissible maximum speed" this is only shown outside built-up areas, without motorways. These statements are also confirmed by analyses of road accident data for 2015 from the federal state of Baden-Württemberg.

Accident Causes VUA [accident recording] (01-69) Responsible for accident in built up areas
Car/van Goods vehicle Bus
n % n % n %
2314 100 370 100 228 100
Exceeding the maximum permissible speed 13 0,6 7 1.9 0 0.0
Inappropriate speed in other cases 157 6,8 32 8,6 26 11,4
Accident Causes VUA [accident recording] (01-69) Responsible for accident outside built up areas
Car/van Goods vehicle Bus
n % n % n %
1213 100 228 100 83 100
Exceeding the maximum permissible speed 25 2,1 6 2,6 1 1.2
Inappropriate speed in other cases 213 17,6 29 12,7 15 18,1
Accident Causes VUA [accident recording] (01-69) Responsible for accident on motorways
Car/van Goods vehicle Bus
n % n % n %
413 100 286 100 23 100
Exceeding the maximum permissible speed 2 0,5 8 2,8 0 0.0
Inappropriate speed in other cases 132 32,0 60 21,0 7 30,4

Source: UDB (accident database of German insurers), motor vehicle liability damage with claims of at least € 15,000 and personal injury

An ISA system which was only designed for use outside built-up areas would have the advantage that due to the less complex and more uniform infrastructure, the number of false alarms by the systems – mainly those of the first generation – would be reduced and therefore acceptance by drivers could be increased.

In association with inappropriate speed, evaluations of accidents have shown that mainly curves and the state of the road (e.g. ice, snow, etc.) are the two decisive factors which cause car accidents outside built-up areas.


According to calculations in the context of the EU cost/benefit assessment, as a system, ISA which influences the driving speed in relation to the permissible maximum speed has the following reduction potential2:

According to ERTICO3 the reduction potential for heavy commercial vehicles is 1% of all accidents and according to a TRL analysis4 for the vehicle classes M2/M3/N2/N3 it is

Furthermore, it is to be expected that a warning that the prescribed speed limit has been exceeded would have a positive effect on overall speed behaviour – including in built-up areas. It is expected that overall, excessive speeds will be reduced by this.

Method of effect:

According to the European Commission ISA systems are driver assistance systems to assist drivers in observing the current speed limits on the section of road which is currently being travelled on. The speed limits are either stored in a digital map in the navigation system and/or are determined by road sign detection. In principle, a differentiation is made between informing, assisting and intervening systems. Over the past decades of discussion, investigations have shown that only assistance systems which can be overridden by drivers have a realistic chance of meaningful implementation to increase road safety.

Furthermore, from the point of view of increasing road safety, it is essentially desirable that ISA systems include an element to assess the "appropriate speed". This can be carried out on the basis of the current traffic situation in the vicinity of the vehicle, the road situation and the road course (curves) as well as the current weather and the state of the road surface.


While digital maps can only be updated with great effort with regard to short-term changes to the permitted speed, for example at roadworks, a further challenge is the detection of static road signs (speed limit signs, signs showing the limits of built-up areas and the adaptive display of systems to influence the flow of traffic).

Inadequately certain detection of road signs, especially due to defective or dirty signs as well as additional signs, e.g. speed limits according to time of day, valid section lengths, valid vehicle types or the assignment of the detected signs to the correct traffic lane are also challenges.

In addition, road signs are not harmonised throughout Europe. This especially applies to supplementary signs. Therefore, even in the years to come, drivers will remain necessary at the decision-making level, e.g. in order to interpret signs which are incorrectly installed, illegible or have been forgotten at cleared roadworks. Solely digital interpretation by the ISA system can create new accident hazards.

In association with the revision of the General Safety Regulation, the European Commission has also revised the infrastructure directive, which has the aim of specifying minimum standards for lane markings and road signs in order to facilitate the introduction of cooperative, networked and automated mobility systems (e.g. ISA)5.


In order to have a high level of user acceptance, the error rate of the systems must be very low. This is the only way to achieve the desired effect on the number of accidents.

For intelligent speed assistants, above all, up-to-date and accurate map data is essential. The correctness of road signs and their cancellation must be reliable. Road signs must also be visible in bad weather conditions.

The acceptance of speed assistants also reduces if they record the driving speeds, communicate these to third parties or can be read out for traffic control purposes.

Legislation and consumer protection:

In the context of the revision of the General Safety Regulation (GSR) the EU Commission requires an assisting ISA system which can be overridden by the driver for all category M and N vehicles as of 2022/2024 (new types/all vehicles)6. The system shall have the following minimum specifications:

The consumer protection test EuroNCAP praises special types of ISA systems. These represent the current state-of-the-art. However, it requires only few additional relevant signs to be recognised in Europe.

Explanation of the DVR position:

If the accelerator pedal is not actuated, e.g. when travelling downhill or with a so-called "coasting function" (freewheeling), this signal cannot be detected. As vehicle regulations normally contain regulations with regard to effect and not design regulations, a tactile accelerator pedal should not be prescribed as the sole technical solution. Because of this, the DVR suggests the use of a suitable attention-gaining human-machine interface, including in commercial vehicles. Further investigations are required for this.

Acceptance problems due to unwarranted warning signals (e.g. "continuous beeping" or "continuous vibration) must be avoided. These should therefore be able to be deactivated or suppressed according to the situation. The display of the maximum permissible speed with is detected by the system should not be able to be switched off. Furthermore, the driver can override the system at any time.



Dr. Walter Eichendorf

1 Carsten, 0., Lei, F., Chorlton, K., Goodman, P., Carslaw, D., Hess, St.: Speed Limit Adherence and its Effect on Road Safety and Climate Change. Final Report, University of Leeds, October 2008.
2 Hynd, D., McCarthy, M., Carroll, J., Seidl, M., Edwards, M., Visvikis, C., Tress, M., Reed, N. and Stevens, A. (TRL): Benefit and Feasibility of a Range of New Technologies and Unregulated Measures in the fields of Vehicle Occupant Safety and Protection of Vulnerable Road Users. Final report, European Commission, Sustainable Growth and EU 2020, 2015.
3 Winder, A.: “ITS4CV” – ITS for Commercial Vehicles. Study of the scope of Intelligent Transport Systems for reducing CO2 emissions and increasing safety of heavy goods vehicles, buses and coaches, final approved version, 9. September 2016, ERTICO-ITS Europe.
4 TRL, CEESAR and ACEA: ISA ‐ Intelligent Speed Adaption for M2/N2 & M3/N3 Accident analysis. Joint accident analysis of TRL, CEESAR and ACEA, 2018.
5 COM(2018) 274 final: Proposal for a DIRECTIVE OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL amending Directive 2008/96/EC on road infrastructure safety management, 17.05.2018, Brussels.
6 Publication 186/18; Proposal for a regulation of the European Parliament and of the Council on type-approval requirements for motor vehicles and their trailers, and of systems, components and separate technical units intended for such vehicles as regards their general safety and the protection of vehicle occupants and unprotected road users, amending Regulations (EU) 2018/ ... and repealing Regulation (EC) No. 78/2009, (EC) No. 79/2009 and (EC) No. 661/2009 Brussels, 17.5.2018 COM(2018) 286 final.
7 The English version states “...the system's prompted vehicle speed...". Instead of the "prompted vehicle speed", the "detected vehicle speed" would be more suitable.