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Scanning for Cars
Pedestrians must usually look both left and right to be sure it is clear to cross in both directions at the same time. This task can be difficult for some people with visual impairments -- if they glance or scan too quickly, they may miss seeing some of the vehicles. This page has suggestions for training students to scan or glance as quickly as possible without missing any vehicles.

Photo shows a man standing at a curb, holding a cane and wearing a vision simulator for narrow visual field.  In the street, about 20-30 feet to his left is a car approaching him. People with less than 5 degrees of central vision:
  • often need to learn to find and scan accurately along the street where vehicles may be approaching. It can sometimes be difficult for them to scan along the street without skipping any spots, and be sure they are looking in the correct places.
  • usually need to scan more slowly than they did when they had more vision because otherwise they'll miss seeing large objects.
    When looking for vehicles, if they glance too quickly from right to left, they'll usually miss seeing cars in what I call the "blind spot" (as shown in the photo to the left -- the man is wearing a simulator for a narrow visual field). This is where the driver would be unable to stop if the student suddenly started to cross -- yikes! (click here if you want to read story.)
  • The "blind spot" where people with narrow visual fields might overlook vehicles is about two car lengths to their left.
    photo shows a woman standing at the curb and looking to her left.  There is a car barely visible approaching from a distance. People with a central scotoma (assuming they are proficient with eccentric viewing):
  • usually need to hold their gaze long enough to see the cars' movement because they cannot see objects of low contrast or clarity unless the object moves. Thus these people cannot glance quickly from side to side to see if there are any cars coming from the left and right because they may miss seeing a car approaching unless they hold their gaze long enough to see it move.
  • The most difficult vehicles to see for people with central scotomas are cars approaching from a distance.

    Most people can learn to scan or glance effectively by using the following exercise:

    1. Find an appropriate street to practice, where the student will be challenged to see the vehicles.

    For all students, if you want to isolate the use of their vision so they can practice their glancing/scanning skills, use a recorded masking sound and/or ear plugs so they are unable to hear the vehicles approaching.

    2. The student stands facing the street.

    3. When the instructor gives the signal, the student turns to look for cars and then looks back and reports whether there are any cars coming. The student should look as quickly as she can without missing any cars.

    The instructor should give the signal to look many times when there is nothing coming, and many times when there is a car or cars that will be difficult to see without scanning properly:

    For narrow central vision, the difficult situation is when there is only one car and it's about 2 car lengths to the left.

    For central scotoma, the difficult situation is when the only cars visible are in the distance. These students need to learn to look quickly both to the right and to the left. Practice first glancing in one direction until the student is skillful, then the other direction, then practice looking quickly in both directions.

    4. If the student misses seeing a car, she should realize she needs to improve and try again:

    For the narrow central vision, scan more slowly and/or scan more accurately along the street.

    For the central scotoma, hold the glance a little longer.


    So far, the exercises on this page are for developing the skill of glancing to determine
  • if there are any vehicles approaching.

    However, the exercises can be adapted develop the skill of glancing to determine
  • if the approaching traffic is too close or fast to allow enough time to cross.

    This should be done after the student has learned to judge speed and distance of the traffic without glancing (see "Assessing Speed and Distance of Vehicles").

    Click here for an exercise to teach students to assess the speed and distance of vehicles at a glance.

    At two-way streets, in which direction do you look first and last?

    For people who take longer than normal to scan or glance in each direction to determine that it is clear to cross, the situation can change drastically in one direction while they are checking in another. For that reason, once they have determined that it is safe in all directions, it is important that the last place they look before starting to cross is toward the traffic approaching in the nearest lane, to make sure it is clear in the lane that they are about to enter. For streets with two-way traffic, that means they look to the left, and after they start to cross, they should look again to the right because in the time that passed while looking to the left, the situation to the right may also have changed.

    Return to Self-Study Guide: Preparing Visually Impaired Students to Assess and Cross Streets with No Traffic Control
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    This page is based on article from the Winter 2003 Newsletter, AER Orientation and Mobility Division