The objective of the present dissertation was to investigate key BEV attributes from a psychological perspective. Regenerative braking and the low noise emission and their impact on user behavior and experience were examined in detail. Findings of paper I, II and IV suggest that drivers quickly adapted to driving with BEVs. Furthermore, both attributes seemed to play an important role in the evaluation of BEVs (paper III).
As discussed above, the tracking and regulating layer of the driving task are altered due regenerative braking and low noise emission. In the future, this could have implications for driver education. If the majority of acceleration and deceleration maneuvers can be executed with one pedal, curricula might have to be adjusted. Especially as conventional braking maneuvers occur less often, it has to be ensured that conventional braking skills are maintained to take over control in emergency situations. Additionally, anticipatory skills appear to be crucial to
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compensate for safety problems arising from the low noise emission. Developing such skills will be even more important in driver education.
9.1 Specific implications of regenerative braking
Findings of paper I and III and studies by other researchers (Schmitz et al., 2013; Eberl et al., 2012) showed that drivers quickly adapted and appreciated a regenerative braking system, which was relatively strong and triggered via accelerator pedal. Using regenerative braking to accurately decelerate to a predefined location also seems to be learnt rapidly. This was shown in an additional study by Witzlack, Cocron, and Krems (2013).
Nevertheless, paper I revealed that the wish to adjust the intensity of regenerative braking corresponded positively with a conventional braking strategy instead of regenerative braking utilization. Offering customizable levels of regenerative braking intensity appear to be a viable solution in this context. The impact of different regenerative braking modes on driver behavior and acceptance should be addressed in future research.
Moreover, some drivers reported on temporary confusion when switching between vehicle types. When driving a conventional vehicle after extended BEV usage, these drivers were expecting the strong drag torque and were then surprised about its absence. Similar effects could occur if regenerative braking fails, temporarily or permanently. In such cases, drivers need to quickly take over control and apply the friction brakes. Similar failures have already been studied in ACC systems, for instance by Nilsson, Strand, Falcone, and Vinter (2013). Initial steps to better understand the impact of regenerative braking failures on driver behavior and acceptance have been undertaken by the EVERSAFE project (http://www.eversafe-project.eu). With respect to system design, appropriate information about the system’s implementation (accelerator, brake pedal or both) and feedback on its status (working vs. not working) seem essential.
Finally, the regenerative braking tested in the dissertation provided direct feedback which could have contributed to its positive evaluation. Due to positive transfer (Fitts & Posner, 1967) of already acquired skills, changing from ICE to BEV driving seems undemanding. Notably, braking and accelerating with one pedal has already been tested in ICE vehicles. Comparable to results discussed in paper I, Nilsson (2002) reported a short learning phase and a positive evaluation of such a pedal solution. Taken together, these findings could provide input how to trigger regenerative braking in EVs.
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9.2 Specific implications of low noise
Findings reported in paper II, III and IV emphasized that drivers were fond of the low noise emission of their BEV. With increasing driving experience, noise as a specific BEV attribute was regarded less as a safety issue and more as a comfort feature. This effect even occurred after a short test drive. Moreover, no substantial differences could be found between experienced and novice BEV drivers in a specific hazard detection task. The latter finding implied that even without extended BEV experience drivers could detect noise related hazards and react accordingly.
These findings could serve as input to the discussion about the safety of EVs. Similar to the US and Japan, the EU (European Commission, 2014) decided on Acoustic Vehicle Alerting Systems (AVAS) to alert pedestrians and bicyclists. The rule will be mandatory after a transitional period of 5 years. As reported in paper II, BEV drivers did not favor artificial sounds. This is comprehensible as noise related incidents were reported rarely and were mostly rated as not too dangerous. Still, given that artificial sounds of EVs will be mandatory soon, it needs to be understood how to implement these systems. Cottrell and Barton (2012) tested different vehicle sounds for pedestrians and found that a warning system, which had to be operated manually, produced higher stress when compared to no external noise and an automated system. Related to the benefit of AVAS, Sandberg (2012) argued that these might result only in marginal safety improvements which could easily be evened out by an inadequate notion of safety among drivers and pedestrians.
To sum up, addressing safety issues due to low vehicle noise appears complex as different perspectives need to be accounted for. The mandatory integration of AVAS might not solve the problem alone. While automated AVAS appear promising, permanent noise at low speeds could compromise the environmental benefit of EVs. Other strategies such as driver and pedestrian training and cooperative systems should also be pursued. A combination of approaches appears most promising to benefit from low noise as important advantage of EVs.
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