Seeing, Communicating, and Speed Control FAQ - Common Questions Answered

Quick answers to the most commonly tested questions from Sections 2.4-2.6 of the CDL manual covering the 12-15 second rule, mirrors, signaling, stopping distance formula, and speed adjustments.

Looking Ahead Questions

Q: What is the 12-15 second rule?

A: Look at least 12-15 seconds ahead—the distance you'll travel in that time. At low speeds this is about one block. At highway speeds it's about a quarter mile. This gives you time to spot hazards and react smoothly without sudden stops or lane changes.

Q: Why is looking far ahead important?

A: Because stopping or changing lanes takes a lot of distance in commercial vehicles. Looking ahead lets you see hazards early and make gradual, safe adjustments. Not looking far enough ahead is a major cause of accidents.

Q: Should you only focus on the distance ahead?

A: No. Good drivers shift attention back and forth, near and far. You need to see both distant hazards and immediate traffic conditions.

Mirror Questions

Q: When should you adjust your mirrors?

A: Check mirror adjustment before every trip. Mirrors can only be adjusted accurately when the trailer is straight. Each mirror should show some part of your vehicle as a reference point.

Q: What are convex mirrors and how do they differ from flat mirrors?

A: Convex (curved, fisheye, spot, bug-eye) mirrors show a wider area than flat mirrors. However, objects appear smaller and farther away than they actually are. Allow for this when judging distances.

Q: When should you check mirrors during a lane change?

A: Check mirrors: (1) before signaling, (2) after signaling to check blind spots, (3) right after starting the lane change, and (4) after completing the change.

Q: What can you check using mirrors besides traffic?

A: Check tires (spot tire fires), cargo security (loose straps, flapping tarps), and your vehicle's position during maneuvers.

Signaling Questions

Q: What are the three rules for using turn signals?

A: (1) Signal early—well before you turn, (2) Signal continuously—keep signal on through the turn, (3) Cancel signal—turn it off after completing the turn.

Q: How should you change lanes?

A: Signal before changing, then change lanes slowly and smoothly. This gives unseen drivers time to honk or avoid your vehicle.

Q: When should you flash your brake lights?

A: Flash brake lights to warn drivers behind when: you see trouble ahead they can't see, making tight turns (you slow more than cars expect), stopping on the road, or driving slowly.

Q: Should you signal other drivers when it's safe to pass?

A: No. Don't direct traffic. You could cause an accident and be liable for damages.

Warning Device Questions

Q: How soon must you place emergency warning devices after stopping?

A: Within 10 minutes of stopping on a road or shoulder.

Q: Where do you place warning triangles on a divided highway?

A: Place at 10 feet, 100 feet, and 200 feet toward approaching traffic.

Q: Where do you place triangles on a two-lane road?

A: Place within 10 feet of front/rear corners, plus 100 feet behind AND 100 feet ahead of the vehicle.

Q: What if there's a hill or curve blocking visibility?

A: Move the rear triangle back so drivers can see it from 500 feet away.

Stopping Distance Questions

Q: What is the stopping distance formula?

A: Perception Distance + Reaction Distance + Braking Distance = Total Stopping Distance

Q: What is the total stopping distance at 55 mph?

A: 419 feet (142 feet perception + 61 feet reaction + 216 feet braking). This is longer than a football field.

Q: What is perception distance?

A: The distance traveled while your eyes see a hazard and your brain recognizes it. Average time is 1¾ seconds. At 55 mph = 142 feet.

Q: What is reaction distance?

A: The distance traveled while moving your foot from accelerator to brake. Average time is ¾ to 1 second. At 55 mph = 61 feet.

Q: What is braking distance?

A: The distance traveled while brakes are applied until the vehicle stops. At 55 mph on dry pavement = 216 feet.

Speed and Stopping Questions

Q: How does doubling your speed affect braking distance?

A: Braking distance becomes 4 times longer. The formula: braking distance increases by the square of speed increase.

Q: If you triple your speed, what happens to braking distance?

A: It becomes 9 times longer (3² = 9).

Q: What happens at 4 times the speed?

A: Braking distance is 16 times longer (4² = 16).

Q: Do empty trucks stop faster than loaded trucks?

A: No. Empty trucks need greater stopping distance because they have less traction. Less weight = less friction between tires and road.

Road Condition Questions

Q: How much should you reduce speed on wet roads?

A: Reduce by one-third (55 mph → about 35 mph). Wet roads can double stopping distance.

Q: How much should you reduce speed on packed snow?

A: Reduce by one-half or more.

Q: What about icy roads?

A: Reduce to a crawl and stop driving as soon as safely possible.

Q: Where do roads get slippery first?

A: Bridges freeze before road surfaces. Shaded areas stay icy longer. Watch out when temperature is near 32°F.

Q: What is black ice?

A: A thin, clear layer of ice that makes the road look wet. Danger signs: temperature below freezing + road looks wet.

Q: How can you check for ice?

A: Open window and feel the mirror, mirror support, or antenna. Ice there = ice on road.

Hydroplaning Questions

Q: What is hydroplaning?

A: When tires lose contact with the road and ride on water instead, like water skiing. You lose steering and braking ability.

Q: At what speed can hydroplaning occur?

A: As low as 30 mph with enough water.

Q: What increases hydroplaning risk?

A: Low tire pressure and worn tire tread (grooves carry water away; shallow grooves don't work well).

Q: What should you do if you hydroplane?

A: Don't brake. Release accelerator, push in clutch to let wheels turn freely, and wait for tires to regain contact.

Curve and Visibility Questions

Q: When should you slow down for a curve?

A: Before entering the curve. Braking in curves can cause skidding.

Q: Can trucks roll over at the posted curve speed?

A: Yes. Trucks with high centers of gravity can roll over even at posted curve speeds.

Q: How should you handle curves?

A: Slow before entering, use a gear that allows slight acceleration through the curve, never exceed posted curve speed.

Q: What's the rule for speed and visibility?

A: Always be able to stop within the distance you can see. Slow down in fog, rain, or when using low beams.

Summary of Key Numbers

Ready to test your knowledge? Start practicing with our Speed Control questions.