Driving automation and driver monitoring

2 Driving automation and driver monitoring

In autonomous vehicles—also called self-driving or fully-automated vehicles—DM plays a critical role as long as the automation allows the driver to have some control over the vehicle. This section describes the interaction between DM and DA in the context of the six levels of DA deﬁned by the Society of Automotive Engineers (SAE) International (185), ranging from 0 (no automation) to 5 (full automation).

Table 1, inspired from the SAE J3016 Levels of Driving Automation Graphic, describes the role of each of the three key actors in the driving task, namely the driver, the driver-support (DS) features, and the automated-driving (AD) features, at each of the six SAE levels. We also integrated into this table a fourth actor, i.e., DM, as its role is crucial at all levels except the highest, to ensure that the state of the driver allows him/her² to perform the driving task safely, when applicable.

Table 1: This table shows the role played by each of the four key actors, i.e., driver, driver-support (DS) features, automated-driving (AD) features, and driver monitoring (DM), at each of the six SAE levels of driving automation (from 0 to 5).


	0	1	2	3	4	5
	No driving automation	Driver assistance	Partial driving automation	Conditional driving automation	High driving automation	Full driving automation


Driver	Driving and supervising DS features			Driving when AD features request it	Driving (if desired) when AD features reach their limits	/

Driver-support (DS) features	Warning and temporary support	Lateral or longitudinal support	Lateral and longitudinal support	/

Automated- driving (AD) features	/			Driving when AD features permit it		Driving

Driver monitoring (DM)	Monitoring	Monitoring with relevant indicators		Monitoring fallback- ready driver	Monitoring when driver in control	/

We now discuss some terminology. In Section 1, we introduced the term “driving automation (DA)” (as a convenient, companion term for DM) and, in the previous paragraph, the SAE-suggested term “automated driving (AD)”. While these two terms seem to further add to a jumble of terms and abbreviations, they both appear in the literature through their corresponding systems, i.e., the “driving-automation system (DAS)” and “automated-driving system (ADS)”. An ADS is a system consisting of the AD features, and a DAS is a system that includes, among other things, both DS features and AD features. One could also view the DS features as constituting a system, but this is not needed here.

In future cars with progressively increasing degrees of automation, the development of DASs—in particular ADSs—should go hand-in-hand with the development of driver-monitoring systems (DMSs). The next four paragraphs complement the information in Table 1.

At Levels 0 to 2, the driver is responsible for the driving task, and he/she may be aided by a variable number of DS features such as automatic emergency braking, adaptive cruise control, and lane centering. At Level 1, the DS features execute the subtask of controlling either the lateral motion or the longitudinal motion of the vehicle (but not both), expecting the driver to perform the rest of the driving task. At Level 2, the DS features execute the subtasks of controlling both the lateral motion and the longitudinal motion, expecting the driver to complete the object-and-event-detection-and-response (OEDR) subtask and to supervise these features. At Levels 0 to 2, a DMS should thus be used continuously. At Levels 1 and 2, for monitoring the state of the driver, a vehicle-related indicator of driving performance should be either avoided or used only when compatible with the DS features that are engaged. The speed cannot, for instance, be used as an indicator of the driver state when an adaptive cruise control is regulating this speed. As more and more DS features are introduced in vehicles, vehicle-related indicators of driving performance become less and less relevant for monitoring the state of the driver, whereas, driver-related parameters (both physiological and behavioral) remain reliable indicators.

At any of Levels 3 to 5, and when the corresponding AD features are engaged, the driver is no longer in charge of the driving task and does not need to supervise them. Additionally, at Level 3, and at any time, the driver must, however, be fallback-ready, namely, ready to take over the control of his/her vehicle when the AD features request it (i.e., ask for it). A DMS should, therefore, be capable of (1) assessing whether the current state of the driver allows him/her to take over the control of his/her vehicle if requested now or in the near future, and of (2) monitoring his/her state as long as he/she is in control. El Khatib et al. (51) discuss the potential need for a DMS even when the vehicle is in control and does not require the driver to supervise the driving or to monitor the driving environment. Whenever the driver has the option of, e.g., engaging in some entertainment activity, he/she must be prepared to regain control in due course. Therefore, at Level 3, despite that the driver is allowed to perform a secondary task, a DMS is still necessary to ensure that the driver is ready to take control at any time. Although the ﬁndings of various research studies are sometimes contradictory, Johns et al. (91) suggest that it may be beneﬁcial for the driver to maintain a certain level of mental workload while his/her vehicle is operated by a DAS, as this could lead to better performance during a transfer of control from automated to manual.

At Level 4, the AD features can only drive the vehicle under limited conditions, but they will not require the driver to respond within some speciﬁed time delay to a take-over request. The operational design domain (ODD) speciﬁes the conditions under which the DAS is speciﬁcally designed to operate, including, but not limited to, (1) environmental, geographical, and time-of-day restrictions, and/or (2) the requisite presence or absence of certain traﬃc or roadway characteristics. Still at Level 4, the AD features are capable of automatically (1) performing a fallback of the driving task and (2) reaching a minimal-risk condition (e.g., parking the car) if the driver neither intervenes nor takes over the driving task within the delay. If the driver decides to respond to the take-over request, one can assume that the DMS would check that his/her state allows for this, even though the SAE J3016 does not say so explicitly.

At Level 5, the driving is fully automated under all possible conditions, and no DMS is required as the driver is never in control, and becomes, in eﬀect, a passenger of the vehicle.

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