Between 20 to 25% of the potential range of an electric vehicle is lost as a psychological safety buffer, according to a study by a doctoral candidate at Technische Universität Chemnitz in Germany. The results of the study, which also suggested that assistance systems could reduce the size of that buffer, were based on more than 400,000 km (249,000 miles) of user experience gathered in the research project “MINI E Berlin powered by Vattenfall”.

The MINI E project was funded by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety. The Professorship of Cognitive and Engineering Psychology of TU Chemnitz was involved in the project from the start, alongside with BMW and Vattenfall and other university partners. During the field study a total of 79 users drove the MINI E for six months. The psychologists of TU Chemnitz conducted qualitative interviews at several points in time. In addition, questionnaires, diary methods and data loggers were used.

Using the results from the project, Thomas Franke developed and tested a model—the adaptive control of range resources (ACOR)—based on transferrable theories and concepts from related areas of applied psychology. A key element in ACOR is the concept of comfortable range, which represents a psychological foundation for the widely discussed concept of range anxiety.

…in everyday life, users with practical electric vehicle experience rarely experience situations in which range anxiety occurs, given a relatively typical mileage for mobility in Germany. Rather, range interaction is characterized by the avoidance, not the experience, of range anxiety (i.e., range stress). Via the analogy to psychological stress, different variables that influence comfortable range are identified. The comfortable range (i.e., an individual’s preferred range safety buffer) appears to be a variable that shows a high inter-individual variance, which partly seems to be predicated upon differing stress resistance.

In sum, the suboptimal range utilization found in previous studies is explained by the proposition that there are three psychological range levels besides the technical range that characterize the transition from the objective physical to the subjective psychological range situation: (1) The competent (i.e., maximum achievable for the user), (2) the performant (i.e., available on an everyday basis) and (3) the comfortable (i.e., actual usable) range. It shows that 20-25% of the range resources that are available on an everyday basis are lost as a psychological safety buffer.

Franke posits that users adopt a preferred coping style when dealing with limited energy resources: “user–battery interaction style (UBIS)”. This is based on the observation, that although EV energy resources are limited, experience of subjectively critical range situations is still relatively infrequent; therefore, EV users seem to be mostly free to choose how they manage their battery resources in everyday use.

The understanding of user-range interaction enables the development of better informed strategies for attaining higher actual battery usage relative to battery capacity, as well as supporting users in the sustainable use of range resources, Franke suggests.
The objective would be to help drivers to fill any gaps between these three range levels (competent, performant and comfortable) and thereby to have more usable range if needed without sacrificing driving pleasure.

[The results imply] that the primary objective of vehicle development should not be to increase battery capacity but to increase the comfortable usable range for the driver. If you consider how much increasing the technical range of electric vehicles by 20 percent costs today, it is very promising if one could achieve such an increase potentially also through optimized information and assistant systems.

The study, which was the basis for Franke’s doctoral dissertation, also covers the preferences for certain range configurations. Here, the pattern of previous research findings indicate that range preferences of car buyers are often far greater than their actual range needs. Franke quantifies the discrepancy based on data from potential electric car customers with practical electric vehicle experience. Among the findings are that:

1. users with practical EV experience do not necessarily have exaggerated range preferences;
2. range preferences decrease with increasing EV experience; and
3. the correlation between actual range needs and range preferences grows as practical experience increases.

This highlights, he sugests, the importance of practical experience for the broad success of sustainable electric mobility systems.

The results of the dissertation are highly relevant for the development of electric mobility systems. Because of the developed theoretical framework the dissertation also contributes to a generally better understanding of the interaction with limited resources. And this is a fundamental issue of our time.