General Knowledge: Hazard Perceptions

16 questions in the bank cover this topic. Everything below is drawn from the sources those questions cite.

Sources: 49 CFR 392.14, TC 21-305-20 para 3-24, TC 21-305-20 para 3-38, TC 21-305-20 para 3-46, TC 21-305-20 para 3-57, TC 21-305-20 para 3-70, TC 21-305-20 para 4-4, TC 21-305-20 para 6-19, TC 21-305-20 para 6-20, TC 21-305-20 para 6-24, TC 21-305-20 para 6-38, TC 21-305-20 para 6-39, TC 21-305-20 para 6-40

What you need to know

392.14 is triggered by hazardous conditions that adversely affect visibility or traction.

Fog is named in the regulation, and reduced visibility alone is sufficient to engage the extreme caution and reduced speed requirements.

Extreme caution in the operation of a commercial motor vehicle shall be exercised when hazardous conditions, such as those caused by snow, ice, sleet, fog, mist, rain, dust, or smoke, adversely affect visibility or traction. Speed shall be reduced when such conditions exist. If conditions become sufficiently dangerous, the operation of the commercial motor vehicle shall be discontinued and shall not be resumed until the commercial motor vehicle can be safely operated.

49 CFR 392.14

Wet leaves act like a lubricant between the tire and the road, so they reduce grip in the same way ice does.

The manual groups them with mud, loose dirt and sand as surface indicators that should make a driver slow down.

Fallen leaves often make roads dangerous because tires are more likely to skid on them when an

TC 21-305-20 para 6-38

The trap is familiarity.

You have driven the road all winter with a clear view through bare branches, and the sight line you rely on quietly disappears over a few weeks in spring. The change happens faster than most drivers notice, so the sight line is gone before it is missed.

Spring and summer foliage may greatly reduce sight distances, especially on curves and at intersections. An operator, though familiar with a road, may not realize how quickly sight distances have been reduced when spring foliage appears.

TC 21-305-20 para 6-40

The hazard is transferred rather than local.

Mud, loose dirt and sand on a paved surface all reduce grip, and the manual lists them as indicators to slow down. That tracked material increases the danger of skidding well beyond the site itself.

The wheels of vehicles turning from dirt roads onto paved roads track mud and dirt onto the pavement. At such places, there is an increased danger of skidding.

TC 21-305-20 para 6-39

Two or three seconds, and at 50 mph three seconds is 219 feet travelled essentially blind.

That is most of a football field covered without seeing.

It takes most operators at least two or three seconds to recover from the effects of glare. At 50 MPH, three seconds means 219 feet.

TC 21-305-20 para 6-19

Each speck scatters the oncoming beam, so the dirt itself becomes the light source.

A windshield that looks fine in daylight can be unusable facing headlights. Each speck scatters the beam until the windshield becomes a wall of light.

A dirty windshield multiplies the effect of glare. In the headlight beams of an approaching vehicle, the specks of dirt on the windshield seem to glow and turn the windshield into a wall of light

TC 21-305-20 para 6-20

Fatigue lengthens recovery, so the two hazards compound: the time of night when glare is worst is the time you are least able to shrug it off.

When an operator is tired, it takes longer to recover from the effects of glare.

TC 21-305-20 para 6-24

Slowing down, before anything clever.

Speed is the one input that makes every other escape easier, and reducing it costs you nothing if the hazard turns out to be nothing.

Many collisions can be avoided by simply slowing down.

TC 21-305-20 para 3-46

Right, and the manual goes further: better to leave the road on the right than to meet an oncoming vehicle head on.

Swerving left puts you into the one place the closing speed doubles.

It is normally safer to swerve to the right than to the left. It is also better to run off the road to the right than to collide head on with an oncoming vehicle.

TC 21-305-20 para 3-46

Rollover, and the faster you go the more room the swerve itself needs.

That is why slowing first is not timid: it widens the range of escapes still available to you. It also needs more distance to turn safely the faster you go.

When swerving a speeding vehicle, there is the risk of flipping the vehicle over. The faster a vehicle is going the more distance it takes to turn safely from a straight path.

TC 21-305-20 para 3-46

A drop-off and reduced traction.

The drop is what catches a steer tire and pulls you further off when you try to come straight back. The drop can be several inches, which is what catches a steer tire.

there may be a drop off of several inches from the edge of the road to the shoulder. Most shoulders provide less traction than the roadway surface.

TC 21-305-20 para 4-4

Yes, with the right procedure.

The crashes come from the instinctive reaction, yanking the wheel back, rather than from being on the shoulder in the first place.

They may be quite narrow and consist of loose gravel, grass, or mud. Despite these variables, pulling off onto the shoulder and returning to the roadway can be done safely.

TC 21-305-20 para 4-4

Vehicles turning or joining, because they enter your path from outside the lane you have been watching.

Brake lights on slow-moving vehicles are on the same list.

Turning vehicles or those entering the highway.

TC 21-305-20 para 3-57

It raises the chance of a death, separately from raising the chance of a crash at all.

Speed is the one factor that worsens both the odds and the consequences.

A high speed driving accident is also more likely to cause a fatality.

TC 21-305-20 para 3-38

For part of it you occupy both lanes, so you are a stationary obstruction to traffic arriving from either direction at whatever speed the road carries.

For part of the turn you occupy the whole road.

However, in some cases (such as a dead-end street or other tight space) the vehicle may have to be turned completely around.

TC 21-305-20 para 3-24

You are entering space you have not inspected and cannot stop within.

Anything already there, unlit or stationary, becomes unavoidable by the time it appears. Anything already there becomes unavoidable by the time it appears.

An operator should never drive so fast that they cannot stop within the distance able to be seen ahead with the headlights.

TC 21-305-20 para 3-70

Check yourself

• Does the extreme caution rule apply when fog reduces visibility but not traction?

• Why are fallen leaves on the road treated as a hazard?

• What is the effect of a hill crest or curve on your sight distance?

• What is the hazard created when vehicles track mud onto the pavement?

• How far do you travel at 50 mph while your eyes recover from headlight glare?

• Why is a dirty windshield worse at night than by day?

• What is the effect of fatigue on your response to glare?

• What does the manual give as the simplest way to avoid many collisions?

• How should you swerve to avoid a collision?

• The risk of swerving at speed in a large vehicle is ______.

• What two hazards does the manual name at the edge of the roadway?

• Can a drift onto the shoulder be recovered safely?

• What does the manual list as a hazard to watch for when looking ahead?

• What is the effect of speed on the outcome of an accident, not just its likelihood?

• What makes turning around in the road a hazard worth avoiding?

• What hazard does driving beyond your headlights create?

Answers are in the practice test for this topic.