Comparison of Usability Between Gear Shifters with Varied Visual and Haptic Patterns and Complexities
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Multimodal Technologies and Interaction Article Comparison of Usability between Gear Shifters with Varied Visual and Haptic Patterns and Complexities Sanna Lohilahti Bladfält * , Camilla Grane and Peter Bengtsson Department of Business Administration, Technology and Social Sciences, Luleå University of Technology, 971 87 Luleå, Sweden; [email protected] (C.G.); [email protected] (P.B.) * Correspondence: [email protected]; Tel.: +46-920-49-33-86 Received: 3 April 2020; Accepted: 27 May 2020; Published: 29 May 2020 Abstract: Shift-by-wire technology enables more options concerning the design, placement and functions of gear shifters compared to traditional gear shifters with manual transmission. These variations can impact usability and driver performance. There is a lack of research regarding the potential advantages and disadvantages of different types of gear shifters. The purpose of this study was to investigate the efficiency and subjective ease-of-use of mono- and polystable joystick gear shifter types at different complexity levels and with full or limited visibility. An experimental study with 36 participants was conducted. The results showed that monostable joysticks, especially those with an I/J-shape, were overall less efficient and easy to use than polystable joysticks. The highest complexity level clearly affected the efficiency for the monostable joystick with an I/J-shape (mono I/J) compared with the other gear shifter types. The monostable joystick with an I/J-shape (mono I/J) was also most affected by reduced visibility at the highest level of complexity, indicating that it was more prone to causing users to take their eyes off the road. Keywords: usability; complexity; shift-by-wire; gear shifter 1. Introduction In 1968, the US National Highway Traffic Safety Administration (NHTSA) alleged that diversity among automatic gear shifters could potentially negatively affect traffic safety [1]. Thus, the NHTSA introduced legislation to prevent errors by standardizing the well-established PRND (Park, Reverse, Neutral and Drive) shift lever sequence. The NHTSA was particularly concerned about shifter errors in association with unfamiliar vehicles and infrequent drivers. This reasoning was in accordance with contemporary research emphasizing that the infrequently used functions in a vehicle should have good learnability and memorability [2]. The linkage between the gear shifter and transmission has traditionally been mechanical, with large and heavy components such as a Bowden cable [3]. Today, the mechanical components can be removed and replaced by electronic shift-by-wire technology, which is becoming increasingly common in modern cars with automatic transmissions [4]. Shift-by-wire gear shifters are often monostable, meaning that the gear shifter will return to one position when the driver releases it. Gear shifters with mechanical transmissions are instead polystable, and the gear shifter will stay in the position to which the driver moves it. Shift-by-wire technology enables new options concerning the design and function of the gear shifter as well as the overall interior design and functionality of the car since the gear shifter is no longer restricted by a mechanical connection [3]. However, as electronic by-wire technology offers car designers increased degrees of freedom, the drivers might face issues regarding usability. A monostable gear shifter lacks the typical spatial haptic feedback when moving the shifter into park, drive or reverse. Monostable shifting requires the driver to devote time to confirm the desired gear position on a display. In a worst-case scenario, this could have fatal consequences. Multimodal Technol. Interact. 2020, 4, 24; doi:10.3390/mti4020024 www.mdpi.com/journal/mti Multimodal Technol. Interact. 2020, 4, 24 2 of 16 The NHTSA concluded that the operation of a monostable shifter is not intuitive, which increases the potential for unintended gear selection [5]. Studies into both manual and automatic gear shifting suggest that drivers might fail to notice traffic information and also make gear-shift errors when gear shifting in attention-demanding or stressful situations [6,7]. A tragic accident caused by a miss-shift occurred in 2015, in which a driver tried to reverse her car that was standing too close a railway crossing. Instead of reversing, the driver drove the car forward; the driver and five train passengers were killed [8]. Based on consumer reports, there have been numerous incidents related to electronic gear shifters [9–12]. One driver described a situation in which he exited the car, believing the gear was in “Park”, and the car began to reverse out of the driveway. Another driver made a similar mistake and reversed into a car [10]. Due to several hundred numbers of unintended vehicle rollaway incidents and alleged crashes associated with a 2014–2015 specific car model, the NHTSA opened an investigation into monostable gear shifters [13]. The problems identified involved more than one model and manufacturer; consequently, the car industry recalled more than a million vehicles on account of traffic safety. The cars were equipped with electronic monostable gear shifters, conveying the selected gear by indicator lights instead of the gear shifter position [13]. According to [14–17], haptics can be used to relieve the visual load and make the vehicle interface more intuitive to use. Findings like these emphasize the importance of haptics when handling secondary tasks such as gear shifting in cars. Consequently, the transition towards monostable gear shifters raises several questions from a traffic safety perspective. There are several studies available on gear shifters [18–20]; however, the implications for usability have not been thoroughly explored. Studies comparing and evaluating monostable and polystable gear shifters are lacking [21,22]. Nevertheless, developers and producers of monostable gear shifters have to continuously make design solutions related to usability and safety issues with the new technology. A study on monostable gear shifters in new vehicles [21] concluded that highly innovative gear shifter designs might confuse drivers and have a negative impact on usability. Furthermore, there seemed to be differences in usability between various monostable designs such as a joystick, stalk, rotary or button shifters. The aim of this paper is to evaluate the usability aspects of monostable versus polystable joystick gear shifters at different complexity levels, with or without visual feedback. Since some cognitive functions, such as the speed of processing information, seems to begin to decline for adults at the age of 20 or 30 with an acceleration of decline at the age of 50 [23,24], only younger drivers under the age of 35 were chosen as participants in this study. More specifically, three hypotheses were tested. Hypothesis 1. There is a difference in efficiency and ease-of-use between shifter types, i.e., monostable and polystable joystick gear shifters. Hypothesis 2. There is a difference in efficiency and ease-of-use between joystick gear shifters at different complexity levels, i.e., with a different number of choices. Hypothesis 3. There is a difference in efficiency and ease-of-use between joystick gear shifters depending on visual feedback. 2. Materials and Methods 2.1. Participants The study comprised 36 participants (29 M; 7 W) with driver’s licenses who were between 19 and 31 years old (M = 22.8; SD = 2.7). All participants drove on a regular basis and had—except for two participants—experience of driving a car with automatic transmission. The participants were students at Luleå University of Technology and received information regarding the study by email. If the students had driver’s licenses, they could apply to participate by choosing an appropriate time and date. Multimodal Technol. Interact. 2020, 4, 24 3 of 16 Participation was voluntary, and the students were not in any position of dependency with the project team. Participants received detailed verbal, as well as written, information about their participation in the study. They were informed about the plan and purpose of the study, the methods to be used, the parties responsible for the study, that participation was voluntary and that they could interrupt and discontinue their participation at any time. The participants received information stating that their anonymity would be maintained and that the study was not measuring individual performance; the study solely measured the performance of the gear shifters. After this, the participants gave their written and verbal consent before actual participation. The study followed Swedish laws regarding conducting experimental research, [25] as well as research rules and guidelines [26]. The participants received a cinema ticket voucher to the value of 135 Swedish crowns. 2.2. Equipment A gear shifter prototype with exchangeable movement patterns was used in the study (Figure1). The gear shifter prototype was developed by Kongsberg Automotive in the form of a joystick, one of the most common gear shifter types in production today. The structural components were made of aluminum with a gimbal joint equipped with ball bearings. The shift force was generated by a spring-loaded plunger acting against an index landscape; the shift pattern and number of shift positions could be altered by exchanging the index component. The panel and knob were made out of 3D-printed, painted polyamide (SLS). The movement patterns were constructed based on vehicle standards regarding movement resistance and the distance between shift positions. The gear shifter visibility was regulated through a blanket fixed on a stick that was lowered over the participant’s right shoulder, which limited their vision but not their hand movement between the steering wheel and gear shifter. The participants were seated in a car seat in front of a desktop driving simulator. The gear shifter was placed on the right-hand side of the participant, at a height and distance that could be assumed to be a common distance in a traditional passenger car with a joystick gear shifter, i.e., approximately 33 cm from the backrest of the seat and 12 cm above the sitting surface of the seat.