General Knowledge: Visual Search
21 questions in the bank cover this topic. Everything below is drawn from the sources those questions cite.
Sources: 49 CFR 392.9, 49 CFR 393.60, TC 21-305-20 para 18-100, TC 21-305-20 para 18-124, TC 21-305-20 para 18-125, TC 21-305-20 para 18-126, TC 21-305-20 para 18-97, TC 21-305-20 para 18-99, TC 21-305-20 para 2-14, TC 21-305-20 para 2-18, TC 21-305-20 para 3-55, TC 21-305-20 para 3-56, TC 21-305-20 para 3-66, TC 21-305-20 para 3-78, TC 21-305-20 para 6-18
What you need to know
392.9(a)(3) requires that cargo not obscure the driver's view ahead or to the right or left sides, with an exception for drivers of self-steer dollies.
Rearward view is addressed through the mirror requirements rather than this provision.
The commercial motor vehicle's cargo or any other object does not obscure the driver's view ahead or to the right or left sides (except for drivers of self-steer dollies).
49 CFR 392.9
393.60(e) returns to sight lines repeatedly.
The dimensional limits exist to serve that test: nothing may sit between you and the road or the signs that govern it. That means your view of the road and of highway signs and signals.
outside the driver's sight lines to the road and highway signs and signals
49 CFR 393.60
Vision, because it is what tells you where your vehicle sits in relation to the road.
Everything else confirms what your eyes have already told you.
Vision is the most important sense used while driving. It makes the vehicle operator aware of the position of the vehicle in relation to the road.
TC 21-305-20 para 18-97
Height and distance.
It is what tells you whether a bridge clears your trailer and how far away that stopped car really is, which acuity alone cannot do.
The vehicle operator needs good depth perception to determine height and distance, good visual acuity to identify terrain features and obstacles that lie along the road
TC 21-305-20 para 18-97
They are different capabilities.
A perfect daylight eye test says nothing about how well you resolve a dark shape at the edge of your headlights.
Wheeled vehicle operators with 20/20 daylight vision may not have adequate night vision.
TC 21-305-20 para 18-97
Technique beats raw acuity.
That is an encouraging finding: the part you can change matters more than the part you cannot.
A vehicle operator with average night vision who uses night vision techniques is more effective than a vehicle operator with superior night vision who does not use these techniques.
TC 21-305-20 para 18-99
Slow and regular.
Quick jumps skip over ground entirely, and your eye needs dwell time at low light to register anything at all.
To scan effectively, scan from right to left or left to right using a slow, regular scanning movement
TC 21-305-20 para 18-124
Off-center, by about 10 degrees.
A night blind spot sits at the center of your vision, so looking straight at a dim object is the one way to make it disappear.
This technique requires viewing an object by looking 10 degrees above, below, or to either side of, rather than directly at an object.
TC 21-305-20 para 18-125
Two or three seconds, then it bleaches to a flat tone and vanishes.
That is why the technique is to keep moving your eyes rather than to stare off-center. None of the figures offered is the one the rule gives.
the image of an object viewed longer than 2 to 3 seconds tends to bleach out and become a solid tone
TC 21-305-20 para 18-126
At night the mirror is most of what you have to the side and rear, so an error in its aim costs you far more than the same error by day.
A badly set mirror then leaves you very little warning of what is behind.
Vision to the sides and the rear is also greatly restricted at night. It is especially important at night that rearview mirrors are properly adjusted.
TC 21-305-20 para 6-18
12 to 15 seconds, measured in time rather than distance so it scales with your speed.
At low speed that is about a block; at highway speed about a quarter of a mile. None of the figures offered is the one the rule gives.
Most good operators look 12 to 15 seconds ahead. This means looking ahead the distance you will travel in 12 to 15 seconds.
TC 21-305-20 para 3-56
A quarter of a mile.
Expressing it in time rather than feet is what makes the rule work at every speed without recalculating.
at lower speeds the distance is about one block and at highway speeds the distance is about a quarter of a mile
TC 21-305-20 para 3-56
Moving between near and far.
Staring far ahead loses what is about to happen beside you; staring close loses the time you need to react at all.
Good operators shift their attention back and forth, near and far.
TC 21-305-20 para 3-56
Both at once.
Awareness is not a single place to look, it is holding the near picture and the far picture together so the two keep updating each other. Awareness is holding them together, not choosing one place to look.
Safe operators are completely aware of their surroundings. They know what is going on in the immediate vicinity of their vehicle and have scanned the areas far enough ahead
TC 21-305-20 para 3-55
Abrupt action, which is the thing that surprises everyone around you.
Looking further ahead does not make you faster, it makes your inputs smaller and earlier.
By not looking ahead, an operator may cause an accident because of having to stop quickly or change lanes quickly.
TC 21-305-20 para 3-56
Ahead.
Everything else is about what is happening to you; the space ahead is about what you are choosing to do next.
the area ahead of the vehicle – the space you are driving
TC 21-305-20 para 3-66
A crest or a curve takes away sight distance, and sight distance is what every judgment about passing, stopping and speed depends on.
You cannot see what you are committing to, which every judgment about passing and speed depends on.
On any curve or hill where visibility is less than 500 feet ahead.
TC 21-305-20 para 3-78
Yellow separates opposing directions, white separates lanes going the same way.
The color tells you what is on the other side before you can see any of it. Yellow separates opposing directions; white separates same-direction lanes.
Yellow centerlines indicate that there is two-way traffic flowing in opposite directions. White lines separate lanes of traffic going in the same direction.
TC 21-305-20 para 2-18
They regulate, guide and warn, which is why they are worth reading rather than just following.
A change in the marking is often the first notice of a hazard ahead.
Pavement markings are used to regulate the flow of traffic, as well as guide and warn operators of possible approaching hazards.
TC 21-305-20 para 2-18
That the people on the red have stopped.
The manual warns about the few who run reds, and a green light protects you legally rather than physically.
always be alert of the few drivers that will run through red lights
TC 21-305-20 para 2-14
The iris, working with the cornea and lens.
It takes time to open, which is the reason your eyes do not adjust instantly when you leave a lit area for a dark road.
The eye is similar to a camera. The cornea, lens, and iris combination gathers and controls the amount of light that enters the retina
TC 21-305-20 para 18-100
Check yourself
- In which directions must your view remain unobscured by cargo?
- Anything mounted inside the windshield must ______.
- Which sense does the manual call the most important while you drive?
- What is depth perception used to judge?
- What does 20/20 daylight vision tell you about your night vision?
- Who sees more at night, by the manual's account?
- How should you move your eyes when scanning at night?
- Where do you look to see a dim object clearly at night?
- How long can you hold off-center vision on an object before it fades?
- Why does your mirror adjustment matter more at night?
- How far ahead should you be looking?
- At highway speed, how far is 12 to 15 seconds of looking ahead?
- Where should your attention sit while driving?
- What does the manual mean by a safe operator's awareness?
- What does failing to look far enough ahead force you into?
- Which space are you actually driving into, and so must watch hardest?
- Why does a hill crest limit what you can safely do?
- What does a yellow line beside your lane tell you?
- What three things are pavement markings doing besides separating lanes?
- What should you still check when your light turns green?
- What part of your eye controls how much light gets in?
Answers are in the practice test for this topic.