Night, Weather, Mountain Grades, and Rail Crossings on the CDL General Knowledge Test

Where these topics sit on the CDL General Knowledge test

Four of the 20 federal General Knowledge areas cover this ground (49 CFR 383.111(a)): night operation, extreme driving conditions such as snow, ice, high wind, and hot weather, mountain driving (safe speed, the right gear, and braking technique), and fatigue and awareness. Railroad crossings come in through the first area, the safe operations regulations, which include the crossing rules in 49 CFR Part 392.

The numbers and methods below come from Washington's CDL guide, which follows the AAMVA model manual. Check your own state's manual, and know your own vehicle. The federal areas and crossing rules are the same for 2027 tests as now; the one pending change, a proposed exception to the crossing stop rule, is explained in the railroad section below.

Downgrades: pick the gear before the grade, then brake in pulses

On a long downgrade, gravity speeds you up. The manuals make engine braking the main way to control speed, with the service brakes as a supplement. Three decisions come in order.

1. Choose a safe speed. It depends on the total weight of the vehicle and cargo, the length and steepness of the grade, road conditions, and weather. Never exceed a posted limit or a "maximum safe speed" sign.

2. Choose the gear before you start down. Shift to a low gear before the descent, not after speed builds. Once you are going too fast, you may not be able to get into a lower gear, or back into any gear, and you lose all engine braking. Forcing an automatic transmission into a low gear at high speed can damage it and also cost you engine braking. The old rule of going down in the gear you would climb in does not always hold, because modern trucks may need a lower gear going down than going up.

3. Brake in short applications. Once you are in the right gear:

Here is a worked example with original numbers. You have chosen a safe speed of 45 mph for a long grade, and you are in a low gear. When the speedometer reaches 45, you brake just hard enough to feel a definite slowdown until it reads about 40, then release. Gravity carries you back to 45, and you repeat, all the way to the bottom. If you are in the right gear, the engine does most of the work and the brake applications stay short. Methods with an order, like this one, are easier to keep when a miss is explained, and full CDL prep is planned with an explanation for every answer.

The tempting wrong answers fail for one reason: heat. Leaning on the service brakes instead of the engine, or starting down in too high a gear and braking hard to make up for it, puts too much heat into the brakes. Hot brakes begin to fade: you have to press harder and harder for the same stopping power, until they may not slow you at all. Brakes out of adjustment stop doing their share first, which overloads the others, so adjustment must be checked often.

If the brakes fail anyway, use an escape ramp: a long bed of loose, soft material, sometimes on an upgrade, built to stop a runaway vehicle. Many steep downgrades have one, signs show where, and the manuals tell you to know their locations on your route. Washington's guide repeats the same braking method in its air brake section, so an air-braked truck uses it too.

The free CDL practice questions include a downgrade item, with every option explained, to try once the method above makes sense.

Slippery roads: black ice, melting ice, and hydroplaning

Traction is what lets you steer and brake, and many conditions cut it. Washington's guide gives rough speed cuts: slow by about one-third on a wet road (from 55 to about 35 mph), by half or more on packed snow, and to a crawl on ice, stopping as soon as you safely can. Wet roads can double stopping distance.

Learn the warning signs of a slippery surface:

• Shaded areas stay icy long after open areas have melted.
• Bridges freeze before the road does, especially when the temperature is near 32°F.
• Melting ice is wetter, and wet ice is far more slippery than dry ice.
• Black ice is a layer of ice so thin and clear that the road looks only wet. If the road looks wet and the temperature is below freezing, assume it may be ice.
• Ice on the vehicle, such as on the mirrors, mirror supports, or antenna, means the road is probably starting to ice up. A lack of spray from other vehicles also suggests ice.
• The first minutes of rain mix water with oil on the road and make it very slippery until the rain washes the oil away.

Hydroplaning happens when water or slush lifts the tires off the road, leaving little or no traction. It can happen at speeds as low as 30 mph with enough water, and it is more likely with low tire pressure or worn tread. To regain control, do not brake. Release the accelerator, and if you drive a manual transmission, push in the clutch so the wheels can turn freely. If your truck has an automatic or automated transmission, follow its maker's guidance for slippery roads. Signs and responses like these are the material the 70 General Knowledge flashcards planned for full CDL prep are meant to keep fresh.

Here is an original scenario. At dawn the temperature is 29°F. The road over an overpass ahead looks wet, but the truck in front of you throws up no spray. The test wants you to read that as black ice: ease off the accelerator well before the overpass, keep the wheel steady, and avoid hard braking. The manuals also say not to use the engine brake or speed retarder on a slippery surface, because it can make the drive wheels skid.

Two more weather points from the same guide. After driving through deep water, keep light pressure on the brakes for a short distance to dry them. In very hot weather, check tires every two hours or 100 miles, and never let air out of a hot tire, because the pressure will be too low once it cools. Skid recovery itself is in the hazards, skids, and emergencies guide.

Night driving, glare, and fatigue

At night your headlights set the limit. Washington's guide says low beams let you see about 250 feet ahead and high beams about 350 to 500 feet. Drive slowly enough to stop within that range, or you will see a hazard too late to stop for it.

• Use high beams when it is safe and legal. Switch to low beams when an oncoming vehicle is within 500 feet, and when you are within 500 feet of a vehicle you are following.
• Avoid glare. Do not look straight at oncoming headlights. Look slightly to the right, at a lane or edge marking. Never answer another driver's high beams with your own.
• Keep the cab dark and the windshield and mirrors clean inside and out. Do not wear sunglasses at night.

Fatigue has its own federal area, and Washington's guide compares it to alcohol and drugs: it impairs vision and judgment. Warning signs include heavy eyelids, repeated yawning, drifting from your lane, and not remembering the last few miles. The guide's answer is blunt: the only safe cure is to get off the road and sleep, and caffeine does not replace rest.

Railroad crossings: required stops, hump crossings, and getting stuck

Federal rules require certain vehicles to stop before every railroad crossing, with a few listed exceptions. The list includes every bus transporting passengers, vehicles carrying certain placarded hazardous materials, and cargo tank vehicles used for hazardous materials, loaded or empty. The driver stops within 50 feet of the tracks but no closer than 15 feet, listens and looks both ways, and crosses in a gear that will not need changing, without shifting on the tracks (49 CFR 392.10). Every other commercial vehicle must approach slowly enough to stop before the nearest rail and may cross only after making sure the way is clear (392.11).

FMCSA has proposed one change. Its May 30, 2025 proposal, followed by a data notice on March 27, 2026, would add an exception to the stop rule at crossings with active warning devices, such as flashing lights or gates, that are not activated. No final rule had been published as of October 28, 2026, so the stop rule applies as written, and your manual's answer is the one to give on the test. Rules in flux are where it helps that full CDL prep, planned for launch, links each explanation to the rule or manual figure it rests on.

Every CDL driver also needs the crossing rules from the manuals:

• Never start across unless you can clear the tracks completely. Washington's guide says a typical tractor-trailer needs at least 14 seconds to clear a single track and more than 15 seconds for a double track.
• Know which rigs can hang up on a raised crossing: low-slung units such as lowboys, car carriers, moving vans, and possum-belly livestock trailers, and a single-axle tractor pulling a long trailer whose landing gear is set for a tandem-axle tractor.
• If you get stuck, get out of the vehicle and away from the tracks first. Then find the emergency number on the signpost or signal housing, call it or 911, and give the crossing's location, including the DOT crossing number if one is posted.

Here is an original scenario. Your lowboy, loaded with a small excavator, grounds out on a steep hump crossing on a country road. No train is in sight, and the tempting move is to rock the rig free or call dispatch from the cab. Both waste the seconds that matter. You leave the cab and move well away from the tracks, then make the call from a safe spot with the crossing's DOT number.

The free practice set also has a stuck-on-the-tracks item, with a reason given for why the other two options fail. For the full list of General Knowledge areas, see the General Knowledge test guide.