New study offers insights into most effective ISA systems

A new study led by Professor Oliver Carsten at the Institute for Transport Studies, University of Leeds, looks at the most effective and user-friendly human machine interface (HMI) options for Intelligent Speed Assistance (ISA).

ISA systems will be required on all new cars, vans, lorries and buses sold in the EU from 2022, as part of an array of mandatory new vehicle safety technologies included in the updated EU General Safety Regulation, agreed last year.

The updated law defines ISA as “a system to aid the driver in maintaining the appropriate speed for the road environment by providing dedicated and appropriate feedback”.  It goes on to say that “it shall be possible for the driver to be made aware through the accelerator control, or through dedicated, appropriate and effective feedback, that the applicable speed limit is exceeded”.  The law also requires that the system can be overridden at any time.

Detailed technical and operational requirements for the system have been left to the European Commission to develop as part of the implementation of the new rules.

The new research, commissioned by ETSC, aimed to find the most effective system designs, by evaluating a number of alternative HMI approaches for ISA, looking both at their effectiveness in terms of promoting speed compliance and at their acceptability to drivers.

The study involved 30 participants testing different variants of ISA on a state-of-the-art driving simulator.  It looked both at how effective each system was at keeping drivers within the speed limit, but also at how the drivers felt about the acceptability of each system.

The results identified three variants of the system as the favoured HMIs, ranked as followed:

• “Speed Control Alone” – whereby the vehicle cuts engine torque once the speed limit is reached, unless the driver deliberately overrides the system by pushing down substantially on the accelerator pedal. This is the approach taken on some existing ISA systems, such as the one found on the Ford Focus, Galaxy and S-Max.  It is also the approach taken on many more basic speed limiter systems on vehicles where the driver can choose their own top speed limit.
• “Haptic Pedal” – in this variant, a system known as force-feedback makes it more difficult to push down on the accelerator pedal once the speed limit has been reached. Again the system could be overridden by pushing down harder on the pedal.
• “Speed Control with Vibrating Pedal” – in addition to the speed control function outlined above, the accelerator pedal would vibrate once the speed limit had been exceeded.

Furthermore the results indicated that neither an “Auditory Warning” only nor a “Vibrating Pedal” without Speed Control are good choices for ISA HMI, as participants considered them the most annoying systems.

“Speed Control Alone” was instead regarded by participants as the most pleasant system and is therefore considered to have reasonable acceptance. Acceptance is deemed important for the overall effectiveness of the ISA system, as drivers are likely to switch off driver assistance systems that they consider unpleasant or annoying. ETSC’s view is therefore that among the three viable HMI options, Speed Control Alone is the best.

ETSC has forwarded the results of the study to the European Commission and TRL, the Transport Research Laboratory who have been commissioned to help develop the technical requirements for ISA.

Click here to download the policy briefing on the results of the study.

The full study can be downloaded from the University of Leeds – Institute for Transport Studies website.