Seeing, Communicating, and Speed Control - Complete Guide
Safe commercial driving requires knowing what's happening around your vehicle, communicating your intentions to others, and controlling your speed appropriately. Sections 2.4-2.6 of the CDL manual cover the critical 12-15 second rule, mirror use, signaling, and the stopping distance formula—all frequently tested on the CDL exam.
Seeing Ahead: The 12-15 Second Rule
Not looking far enough ahead is a major cause of accidents.
How Far to Look
Look at least 12-15 seconds ahead—the distance you'll travel in that time.
| Speed | 12-15 Seconds Ahead |
|---|---|
| City/low speed | About 1 block |
| Highway speed | About 1/4 mile |
Key Point: Looking ahead doesn't mean ignoring what's closer. Good drivers shift attention back and forth, near and far.
What to Look For
- Vehicles entering highway or your lane
- Brake lights from slowing vehicles
- Traffic signals that may change
- Hazards requiring speed or lane changes
Mirrors: Adjustment and Use
Mirror Adjustment
- Check adjustment before every trip
- Adjust only when trailer(s) are straight
- Each mirror should show some part of your vehicle as a reference point
When to Check Mirrors
Regular checks: Every 5-8 seconds to know traffic positions and spot vehicles in blind spots.
Special situations requiring extra mirror checks:
| Situation | Why |
|---|---|
| Lane changes | Check no one is alongside or passing |
| Turns | Ensure rear of vehicle won't hit anything |
| Merges | Verify gap is large enough |
| Tight maneuvers | Ensure clearance |
Lane Change Mirror Sequence
- Before signaling—check for room
- After signaling—check blind spots
- After starting change—double-check path
- After completing change—verify position
Convex (Curved) Mirrors
- Show wider area than flat mirrors
- Objects appear smaller and farther away than they really are
- Allow for this difference when judging distances
Communicating Your Intentions
Signaling Turns
Three rules for turn signals:
- Signal early—well before you turn
- Signal continuously—keep both hands on wheel during turn
- Cancel signal—after completing the turn
Signaling Lane Changes
- Signal before changing lanes
- Change lanes slowly and smoothly
- Gives unseen drivers time to react
Warning Others When Slowing
Flash brake lights to warn drivers behind you when:
- You see trouble ahead they can't see
- Making tight turns (you must slow more than cars expect)
- Stopping on the road
- Driving slowly—use four-way flashers if legal
Important: Don't direct traffic or signal others when it's safe to pass. This could cause an accident and cost you thousands.
Communicating Your Presence
| Situation | Action |
|---|---|
| Passing vehicles/pedestrians/bicyclists | Light tap on horn (assume they don't see you) |
| Hard to see (dawn, dusk, rain, snow) | Turn on low beam headlights |
| Parked on roadside | Four-way flashers + warning devices within 10 minutes |
Emergency Warning Device Placement
On divided/one-way highway:
- 10 feet, 100 feet, and 200 feet toward approaching traffic
On two-lane/undivided road:
- 10 feet from front/rear corners
- 100 feet behind AND ahead of vehicle
Near hill or curve:
- Place rear triangle so drivers can see it 500 feet away
Stopping Distance Formula
Perception Distance + Reaction Distance + Braking Distance = Total Stopping Distance
The Three Components
| Component | Definition | At 55 mph |
|---|---|---|
| Perception Distance | Distance traveled while seeing and recognizing hazard | 142 feet (1¾ seconds) |
| Reaction Distance | Distance traveled while moving foot to brake | 61 feet (¾-1 second) |
| Braking Distance | Distance traveled while braking | 216 feet |
| TOTAL | Complete stopping distance | 419 feet |
Exam Tip: At 55 mph, total stopping distance is 419 feet—longer than a football field (360 feet).
Effect of Speed on Stopping Distance
When you double your speed, braking distance is 4 times longer.
| Speed Comparison | Impact/Braking Distance |
|---|---|
| 20 mph (baseline) | 1x |
| 40 mph (2x speed) | 4x longer |
| 60 mph (3x speed) | 9x longer |
| 80 mph (4x speed) | 16x longer |
The formula: Braking distance increases by the square of the speed increase.
Effect of Weight on Stopping Distance
- Heavier vehicles need more braking work and generate more heat
- BUT: Empty trucks require greater stopping distances than loaded trucks
- Why? Empty vehicles have less traction because less weight pushes tires onto road
Key Point: Brakes, tires, and suspension are designed to work best when fully loaded.
Speed and Road Conditions
Slippery Surface Speed Reductions
| Condition | Speed Reduction |
|---|---|
| Wet road | Reduce by 1/3 (55 mph → 35 mph) |
| Packed snow | Reduce by 1/2 or more |
| Ice | Reduce to a crawl, stop when safe |
Wet roads can double stopping distance.
Identifying Slippery Surfaces
- Shaded areas—stay icy after open areas melt
- Bridges—freeze before roads (watch near 32°F)
- Melting ice—wet ice is more slippery than dry ice
- Black ice—looks wet, actually thin clear ice
- Just after rain starts—water mixes with road oil
Checking for Ice
Open window and feel mirror, mirror support, or antenna. Ice there = icy road.
Hydroplaning
- Tires lose contact with road surface
- Can occur as low as 30 mph with enough water
- More likely with low tire pressure or worn tread
- Response: Release accelerator, push in clutch, don't brake
Speed and Curves
- Slow before entering—braking in curves can cause skid
- Don't exceed posted curve speed limits
- Trucks with high center of gravity can roll over at posted curve speeds
- Be in gear that allows slight acceleration through curve
Speed and Visibility
Always be able to stop within the distance you can see.
- Fog, rain, darkness require slower speeds
- Low beams show less distance than high beams—slow down when using low beams
Frequently Asked 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 city speeds, this is about one block. At highway speeds, about a quarter mile. This gives you time to identify hazards and react smoothly rather than making sudden stops or lane changes.
Q: What is the stopping distance formula?
A: Perception Distance + Reaction Distance + Braking Distance = Total Stopping Distance. At 55 mph: 142 feet (perception) + 61 feet (reaction) + 216 feet (braking) = 419 feet total.
Q: How does doubling your speed affect stopping distance?
A: Doubling your speed makes braking distance 4 times longer. Tripling speed makes it 9 times longer. This is because braking distance increases by the square of the speed increase.
Q: Do empty trucks stop faster than loaded trucks?
A: No. Empty trucks require greater stopping distances because they have less traction. The reduced weight means less friction between tires and road. Brakes and tires are designed to work best when fully loaded.
Q: How much should you reduce speed on wet roads?
A: Reduce speed by about one-third on wet roads (55 mph → 35 mph). Wet roads can double stopping distance. On packed snow, reduce by half. On ice, slow to a crawl.
Q: What is hydroplaning and when does it occur?
A: Hydroplaning is when tires lose contact with the road due to water. It can occur at speeds as low as 30 mph with enough water. More likely with low tire pressure or worn tread. Response: release accelerator, push in clutch, don't brake.
Q: Why do objects in convex mirrors appear farther away?
A: Convex (curved) mirrors show a wider area but make objects appear smaller and farther away than they actually are. Always allow for this when judging distances in convex mirrors.
Q: When must you place emergency warning devices?
A: Within 10 minutes of stopping on a road or shoulder. Place at 10, 100, and 200 feet toward approaching traffic on divided highways. On two-lane roads, place 100 feet behind AND ahead.
Q: What three rules apply to using turn signals?
A: (1) Signal early—well before the turn, (2) Signal continuously—through the entire turn, (3) Cancel signal—after completing the turn.
Q: How do you check for ice on the road?
A: Open your window and feel the front of the mirror, mirror support, or antenna. If there's ice on these surfaces, the road is probably starting to ice up.
Next Steps
Memorize the key numbers:
- 12-15 seconds looking ahead
- 419 feet stopping distance at 55 mph
- Speed squared = braking distance multiplier
- 1/3 speed reduction for wet roads
Ready to test your knowledge? Start practicing with our Speed and Space Management questions.