Appendix A: 
Functional Abilities Addressed 
in Pilot Driver Screening Programs

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 surface.
  
• 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.

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