Driver Screening and Evaluation Program
Volume III: Guidelines for Motor Vehicle Administrators
Functional Abilities Addressed
in Pilot Driver Screening
The particular functional changes at the center of identification and assessment programs now
undergoing pilot testing in the U.S. and abroad can be listed and briefly described as follows.
- Reduced visual acuity -- pertains to the aspect of vision that is used to resolve fine detail;
used to see roadway targets that have high brightness or color contrast with the surrounding
background area, and which have sharply defined edges, such as letters on road signs.
- Reduced visual contrast sensitivity -- pertains to the aspect of vision that is used to see
targets that do not differ greatly in brightness or color from the surrounding back-ground area
and that may have "fuzzy" or ill-defined edges, such as the edge of the road where there is
a worn/faded or missing edge stripe and the color of the shoulder is similar to the paved
- Increased susceptibility to glare/slower glare recovery -- pertains to stray light entering the
eye that masks or interferes with focal vision, and the length of time after exposure to the
disabling effects of glare that roadway targets can be seen as well as before the glare was
introduced; this commonly results at night from oncoming headlights or headlights viewed
in rearview mirrors, but sun glare can produce similar problems during daytime driving.
- Reduced sensitivity to changes in angular size and motion -- pertains to judgments about how
far away an object is and how fast it is moving--for example, a car approaching as you wait
to turn left at an intersection; the accuracy of such judgments depends upon how quickly and
accurately a person's brain can interpret changes in the size of the image that is formed on
the retina at the back of the eye when his/her gaze is focused on a distant object.
- Poorer visual "pattern perception"/visualization of missing information -- pertains to an
ability to extrapolate from the visual elements in a scene to "construct" a whole image from
only partial information, as may be required to recognize a sign or other traffic control
device, or to appreciate the safety threat represented by a vehicle or pedestrian that is
partially obstructed (e.g., by a building or parked car) at the side of the road, but about to
move into the driver's path.
- Less efficient visual search -- pertains to the speed with which a person can direct his/her
gaze from one location to another where experience dictates that information important to
the task at hand will be found, as when a driver scans the roadway scene ahead to look for
a sign, landmark, or other directional information.
- Reduced area of visual attention -- pertains to that portion of the overall visual field where
a person not only is capable of seeing an object, but also is likely to pay attention to it, and
recognize and respond to the object in a brief enough time to avoid a crash if it is a traffic
hazard; the risk of colliding with vehicles, pedestrians, and cyclists entering from the side
of the road or at an intersection increases significantly as the area of visual attention shrinks.
- Impaired selective attention ability -- pertains to the ability--on a continuing basis--to filter
out the less important events and information while driving and "home in" on just those few
things that are most safety-critical at each instant; though not done on a conscious level, this
is absolutely necessary for the anticipation of and effective response to hazards, so that an
avoidable conflict does not become an emergency.
- Less efficient divided attention/slower attention switching -- pertains to the ability to monitor
and respond effectively to multiple sources of information at the same time; for example, a
driver entering a freeway must track the curvature of the ramp and steer appropriately, keep
a safe distance behind the car ahead, and check for gaps in traffic on the highway, while at
the same time accelerating just enough to permit a smooth entry into the traffic stream.
- Less efficient working memory processes -- pertains to a driver's ability to think about and recall
information while driving that will be needed at a later time, without any lapses in safely
controlling his/her vehicle; for example, being able to remember and apply a simple set of
navigational instructions memorized before a journey while driving in heavy traffic.
- Loss of limb strength, flexibility, sensitivity, and/or range of motion -- pertains to quickly
shifting (the right foot) from accelerator to brake when the situation demands, and applying
correct pressure for appropriate speed control; also, these physical abilities are needed (for
arm movements) to safely maneuver the car around obstacles.
- Reduced ability to rotate head/neck -- pertains to a driver's physical ability to orient his/her
gaze in each direction from which a vehicle conflict may occur in a given situation; this
includes the familiar "left-right-left" check before crossing an intersection, as well as looking
over one's shoulder before merging with traffic or changing lanes.