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Mobility & Transport - Road Safety

Advanced Driver Assistance Systems (ADAS) can provide personal assistance in a road environment that cannot always take into account the possibilities and limitations of the older driver. An analysis of the strengths and weaknesses of the older driver has shown that the most important need for support stems from the difficulties that older drivers have to:

  • Judge whether fellow road users are approaching the same intersection and at what speed
  • Notice other road users while merging and changing lanes
  • Notice traffic signs and signals
  • React quickly in a complex traffic situation.

These difficulties stem from functional limitations such as a decrease in motion perception, peripheral vision, flexibility of head and neck, selective attention, and speed of processing information and decision making. ADAS that can compensate for these limitations, can contribute to a reduction of the crash involvement of older drivers. Such ADAS should have one or more of the following functionalities:

  • Draw attention to approaching traffic
  • Signal road users located in the driver's blind spot
  • Assist the driver in directing his attention to relevant information and/or
  • Provide prior knowledge on the next traffic situation.

ADAS that have these functionalities could improve the safety of older drivers. Examples of such systems are collision warning systems aimed at intersections and in-vehicle signing systems. There are, however, also ADAS that could improve the mobility of the older driver, or may reduce his injury severity. Examples of those systems are vision enhancement systems and mayday systems.

Using ADAS to improve the safety or mobility of the driver involves more than making sure that the supported subtask is carried out safely. It also involves that the support provided does not have any negative effects on the other elements of the driving task. Examples of negative side effects are increased task load due to a bad design of the human machine interface, and the effects of behavioural adaptation. ADAS that could improve road safety for older drivers

Several studies have mentioned ADAS that may be able to provide tailored assistance for older drivers. ADAS that, according to Mitchell and Suen, may be able to provide assistance for the difficulties resulting from limitations in motion perception, peripheral vision, selective attention and decreased speed of processing information and decision making are summarized in the table below:

Functionality ADAS
Draws attention to approaching traffic
  • Collision warning systems aimed at intersections
  • Automated lane changing and merging systems
Signals road users located in the driver's blind spot
  • Automated lane changing and merging systems
  • Blind spot and obstacle detection systems
Assists the driver in directing his attention to relevant information
  • In-vehicle signing systems
  • Special intelligent cruise control
Provides prior knowledge on the next traffic situation
  • Systems that give information on the characteristics of complex intersections the driver is about to cross

It turns out, however, that many of these systems are still being developed and not much research has been done on user acceptance and the effects on road user behaviour. As a result, little can be said on whether these systems - when available - will actually be used by older drivers and will actually improve their safety [23].


ADAS that could enhance mobility or lower injury severity

Systems that could enhance the mobility of older drivers, or that could lower their injury severity, are:

  • Night-vision enhancement systems
  • Navigation systems
  • Mayday systems

These systems seem to be helpful for drivers who have difficulties driving in the dark or driving in an unfamiliar area, and for those who have subjective feelings of insecurity respectively. Hence, these systems are particularly suitable to enhance the mobility of older people. Mayday systems can also reduce the time to medical treatment, thereby reducing injury severity. Usage of the other two systems may also lead to a reduction of the crash rate of older drivers by compensating for impaired nighttime visual acuity and by preventing search behaviour respectively. Whether this reduction in crash rate will also lead to a reduction in the number of victims is dependent on the magnitude of the reduction in crash rate. The latter reduction should be larger than the increase in mobility due to system usage (see also behavioural adaptation).


User acceptance

Several studies have shown that older drivers are to a large extent willing to consider using and buying ADAS that meet an existing need, such as reversing aids, and collision warning systems that are aimed at the prevention of crashes on intersections. Furthermore, older drivers are also willing to accept systems that (partly) take over vehicle control (like automatic speed or distance adjustment) or that give feedback messages. These results indicate that older drivers will also accept ADAS as a means to improve their safety. Whether the introduction of one of those systems will actually result in a reduction of the number of crashes will also be dependent on the design of that particular system.


Preconditions for safe use of ADAS by older drivers

Knowing which types of ADAS have the most potential to improve the safety of older drivers is not enough to actually improve their safety. Besides the fact that the user will have to accept, buy, use and trust the system, the driver should also be able to understand the information the ADAS sends to him (via a display or by sound). In case more than one ADAS is installed in a car, the systems should work together instead of fighting for the attention of the driver and giving him conflicting information. The support provided by the system(s) should not have any negative safety consequences. These preconditions can be met by complying with the guidelines for human machine interfaces, by making sure that ADAS work together, and by being aware of the effects of behavioural adaptation.

Design principles for the human machine interface

Older drivers are more susceptible to the consequences of poorly defined ADAS than younger drivers (Stamatiadis 1994; cited in Regan et al.). They generally need more time to carry out secondary tasks while driving. Hence it is critically important to bear in mind the possibilities and limitations of older drivers while designing the human machine interface for ADAS. There are several reports available which describe the current guidelines (see Green for an overview). have summarized these guidelines and in addition included a section on guidelines for older drivers. The design guidelines for older drivers are summarized below, along with the functional limitations of older adults they take into account:

Functional limitations Relevant design principles
General sensory deficits Use redundant cues, like auditory, visual and tactile feedback
Visual acuity Increase character size of textual labels
Colour vision Use white colours on a black background
Diminished low-light vision Use supplemental illumination for devices used in low-light conditions
Sensitivity to glare Use matt finishes for control panels and antiglare coating on displays
Hearing Use auditory signals in the range of 1500-2500 Hz range
Depth perception Where depth perception is important, provide non-physical cues, such as relative size, interposition, linear position and texture gradient
Selective attention Enhance the conspicuity of critical stimuli through changes of size, contrast, colour or motion
Perception-reaction time Give the user sufficient time to respond to a request by the system and provide advanced warnings to provide the driver with enough time to react to the on-coming traffic situation
Hand dexterity and strength Use large diameter knobs, textured knob surfaces and controls with low resistance

Functional limitations and relevant design principles (based on Caird et al. (1998) and Gardner-Bonneau and Gosbee (1997))

Whereas the guidelines in this table have all been selected based on the older adult's functional limitations, it should be kept in mind that designers should also take advantage of the experience that older drivers have. This can be accomplished by using familiar features that are common to them, such as traffic-related icons or features that are common to other products used by older adults.

ADAS should work together

When car owners install more than one ADAS in their car, the presence of several displays may introduce new problems. Each display will attract the attention of the driver. Older drivers will suffer the most from that, since age differences become more evident as tasks are becoming more complex. This will result in longer reaction times (see for example McDowd and Craik). Messages sent simultaneously from different ADAS will increase the pressure on the driver even further. Summing up, the presence of several, independently functioning systems increases the task load, leading to an effect in the opposite direction of what was the objective of the implementation of the ADAS: lowering the task load.

Some sort of coordination between the installed ADAS may overcome these difficulties. In addition, it can also prevent systems from sending conflicting instructions or, even worse, carrying out conflicting actions. The coordination between systems can be implemented in several ways. Heijer et al suggested that one ADAS should be able to support the driver in a set of problematic situations instead of separate ADAS each supporting the driver in a different situation. Another way of implementing coordination between ADAS uses mediation by a system that decides when which system is allowed to pass what kind of information in what kind of way. Several examples of mediators have been described in the literature.

Behavioural adaptation

The phenomenon of behavioural adaptation implies that people adapt their behaviour to some of the improvements of a system by taking bigger chances (See Dragutinovic, Brookhuis, Hagenzieker, and Marchau for an overview of the behavioural adaptation effects in response to Advanced Cruise Control). The term behavioural adaptation originates from Evans but the phenomenon is also known under the terms risk compensation and risk homeostasis. A form of behavioural adaptation that could arise among older adults, is the withdrawal of compensatory behaviour. This can be illustrated by the introduction of vision enhancement systems. Older drivers generally compensate for their impaired night-time visual acuity and sensitivity to glare by avoiding to drive at night. As a result, the number of crashes involving older drivers at night is relatively low. When the large-scale introduction of night vision enhancement systems makes older adults drive at night again, this will increase their mobility and improve their quality of life. However, it remains to be seen whether the use of night vision enhancement systems will provide similar risk compensation for impaired night-time visual acuity to the older driver's compensation strategy of not driving at night.