Study guide
Darkness, weather, grades, and rail crossings each strip away some of the margin a commercial driver normally relies on, and cargo that is overweight or badly secured removes margin from the inside. This chapter covers night and winter driving, mountain descents and escape ramps, the railroad crossing rules, and the cargo weight, balance, and securement basics every general knowledge candidate must know.
Night Driving and Headlight Limits
Night driving is harder for one blunt reason: you can only respond to what you can see, and at night you see less, later. Low-beam headlights show you about 250 feet of road; high beams show roughly 350 to 500 feet. The operating rule follows directly — never drive so fast that you could not stop within the distance your headlights reveal. At 55 mph you need over 400 feet to stop, which is more than low beams show you, so speed has to come down after dark. Use high beams whenever it is safe and legal, because many drivers underuse them, but dim for oncoming vehicles and when following someone; most state manuals put the dimming distance at about 500 feet, though the exact figure varies by state. Glare works against you from both directions: meeting bright lights can leave your eyes needing seconds to recover, and at 55 mph you travel about 80 feet every second, so two seconds of glare recovery means more than 160 feet driven half-blind. Do not look directly into oncoming headlights — shift your eyes toward the right edge of your lane until the vehicle passes. Help your eyes with maintenance: a dirty windshield multiplies glare, and dirty headlamps can deliver only half the light they should, so clean both during the pre-trip. Keep instrument lights dimmed, never wear sunglasses at night, and be honest about fatigue, which arrives faster in the dark and degrades exactly the vision and judgment night driving demands most.
Fog, Winter, Black Ice, and Hot Weather
The manual's best advice on fog is simple: do not drive in it if you can avoid it — pull off in a safe place and wait. If you must drive, slow down, use low beams and fog lights, never high beams, which bounce back off the fog, and do not stop in a travel lane. Winter driving starts with the winter inspection: coolant level and antifreeze strength, defrosters and heater, wipers and washer fluid, tire tread and tire chains where mountain routes require carrying them — chain laws vary by state and season — plus lights, reflectors, and windows kept clear of ice and snow. On the road, everything gets gentler: turn, brake, and accelerate as smoothly as possible, and remember the speed rules from chapter two — half speed or less on packed snow, a crawl on ice. Bridges freeze before roadways because cold air reaches them from below. Black ice is a thin, clear layer that lets the dark pavement show through, so the road looks merely wet; when the temperature is near freezing and mist or drizzle is falling, suspect it, and check for ice building on your mirrors, antenna, or wiper blades as an early warning. Hot weather brings its own inspection rhythm: check tires about every two hours or every 100 miles, because heat builds pressure. Never bleed air from hot tires — the pressure will be too low once they cool — and if a tire is too hot to touch, stay stopped until it cools. Watch for bleeding tar, which is slippery, watch the engine temperature gauge, and never remove a radiator cap from a hot, pressurized cooling system.
Mountain Driving and Escape Ramps
In mountain driving, gravity is the extra passenger. Uphill it slows you — downshift and let faster traffic pass. Downhill it accelerates you, and this is where new commercial drivers get into the most trouble, because the service brakes on a heavy vehicle can only absorb so much heat. Used continuously on a long grade, they overheat and fade: you push harder and harder for less and less braking, until there may be almost none. The defense is to let the engine do the braking. Go down in a low gear selected before the descent begins — never try to downshift partway down, because you may not get the gear and will be coasting with no engine braking at all. On older trucks the habit was the same gear down as up; modern engines and transmissions usually need a lower gear going down than the climb required. Your safe speed depends on the load, the vehicle, the steepness and length of the grade, and the weather. Once you have it, use the proper braking technique: apply the brakes firmly enough to feel a definite slowdown, release when your speed drops about 5 mph below your safe speed, and repeat as speed climbs back — brief, firm applications with cooling time between, instead of a long light drag that cooks the linings. If braking is ever failing on a grade, use the escape ramp. Ramps of loose gravel, sand, or an upgrade are built to stop runaway vehicles with modest damage. A driver named Devon who takes the ramp trades a tow bill for his life; drivers who gamble on the next curve often lose far more.
Railroad-Highway Crossings
Railroad crossings come in two kinds. A passive crossing has no gates or flashing lights — only signs such as the crossbuck — so the decision to cross is entirely yours. An active crossing controls traffic with flashing red lights and often gates. Either way, the physics are fixed: a freight train moving at highway speed can need a mile or more to stop, so the train will never yield, and trains are deceptively fast — their size makes them look slower and farther away than they are. Expect a train on any track, in either direction, at any time, and never rely on hearing one; modern cabs are loud. Slow down, look both ways, and never shift gears while any part of the vehicle is on the tracks, because a missed shift can leave you stalled in the worst spot on earth. Do not start across unless there is room for your entire vehicle plus clearance on the far side — remember that trains overhang the rails by at least three feet on each side — and know that low-slung equipment can hang up on raised crossings. Certain vehicles, including buses carrying passengers and trucks hauling placarded hazardous materials, must stop at every crossing, between 15 and 50 feet from the nearest rail, then cross in a gear low enough to clear without shifting; the exact list of vehicles that must stop varies somewhat by state. If you ever become stuck on the tracks, get out immediately, walk away from the tracks at an angle toward the direction any train would come from — so debris flies past you, not at you — and call the Emergency Notification System number posted on the blue sign at the crossing, or 911.
Cargo Weight, Securement, and Hazmat Placards
Even if someone else loads the trailer, the driver is responsible for the cargo: not overloaded, properly balanced, and secured so it cannot shift or fall. Start with the weight vocabulary. Gross vehicle weight (GVW) is the loaded weight of a single vehicle; gross combination weight (GCW) is the loaded weight of a tractor plus trailer plus cargo; GVWR and GCWR are the manufacturer's rated maximums for each. Axle weight is how the load presses down through each axle onto the road, and states set the legal maximums for axle and gross weights, so limits vary along your route. Balance matters as much as totals: a high center of gravity makes rollover more likely on curves and ramps, so load heavy freight low and spread it evenly. Too little weight on the drive axles means poor traction; too much on the steering axle means hard steering and wear. Securement uses blocking and bracing to stop movement and tie-downs to clamp cargo to the deck. The federal standards say cargo needs at least one tie-down for every ten feet of cargo length, a minimum of two tie-downs no matter how small the item, and a combined working load limit of at least half the cargo's weight. A header board protects you from forward-crushing cargo in a hard stop, and covers protect people from spills — many states require covering loads that could leak or blow out. Inspect the cargo before starting, within the first 50 miles, and then every three hours or 150 miles and after each break. Finally, hazmat basics apply to every driver: diamond-shaped placards on all four sides of a vehicle identify hazardous cargo, and driving a placarded vehicle requires a hazmat endorsement — without one, refuse the load.
Key terms
- Black ice
- — A thin, clear layer of ice that lets dark pavement show through, making an icy road look merely wet.
- Brake fade
- — Loss of braking power when overused brakes overheat on long downgrades, requiring more and more pedal pressure for less effect.
- Escape ramp
- — A bed of loose gravel or an upgrade beside a mountain road built to safely stop a vehicle whose brakes have failed.
- Passive crossing
- — A railroad crossing without gates or flashing lights, where the driver alone decides whether it is safe to cross.
- Emergency Notification System (ENS) sign
- — The blue sign at rail crossings listing the phone number and crossing ID used to warn the railroad of a vehicle stuck on the tracks.
- Gross vehicle weight rating (GVWR)
- — The manufacturer's maximum rated weight for a single vehicle and its load.
- Gross combination weight rating (GCWR)
- — The manufacturer's maximum rated weight for a tractor, its trailer, and the cargo together.
- Center of gravity
- — The point where cargo weight balances; the higher it sits, the more easily the vehicle rolls over in curves.
- Working load limit (WLL)
- — The rated strength of a tie-down; the combined limit of all tie-downs must be at least half the cargo's weight.
- Header board
- — The barrier at the front of a trailer or behind the cab that protects the driver from cargo shifting forward in a sudden stop.
- Placard
- — The diamond-shaped hazard sign displayed on all four sides of a vehicle carrying regulated amounts of hazardous materials.
- Bleeding tar
- — Road tar softening and rising to the surface in high heat, creating a slippery film on the pavement.
Exam tips
- Pair the headlight numbers with the rule: low beams show about 250 feet, high beams about 350 to 500, and your speed must let you stop within what you can see.
- The downgrade braking sequence is tested often: low gear chosen before the descent, brake firmly to a definite slowdown, release at about 5 mph below your safe speed, repeat.
- For required railroad stops, the answer is between 15 and 50 feet from the nearest rail, and never shift gears while crossing the tracks.
- Memorize the securement trio: one tie-down per ten feet of cargo, at least two tie-downs always, and combined working load limit of at least half the cargo weight.
- Cargo inspection timing is a favorite: before the trip, within the first 50 miles, then every three hours or 150 miles and after every break.