If English is your second language, the hard part of the Texas CDL knowledge test is usually not the traffic law. It is the fifty or sixty words the test uses as though everyone already knows them: slack adjuster, glad hands, out of adjustment, bobtail. You can understand how air brakes work perfectly well in your first language and still lose a question because you did not know that "secure" in an inspection question means bolted down, not safe.
Two things make this vocabulary matter beyond the exam room. Federal driver qualification rules require that a commercial driver "can read and speak the English language sufficiently to converse with the general public, to understand highway traffic signs and signals in the English language, to respond to official inquiries, and to make entries on reports and records" (49 CFR 391.11(b)(2)). Since June 25, 2025, a violation of that paragraph has been an out-of-service violation under the North American Standard Out-of-Service Criteria; the governing FMCSA enforcement memorandum was reissued on April 16, 2026, and CVSA amended the criteria on April 19, 2026 to follow whatever FMCSA guidance is current. On August 10, 2026 FMCSA published a proposed rule to write the out-of-service consequence into the regulation itself, with comments due October 9, 2026. Texas DPS has separately announced that it gives CDL and CLP knowledge tests in English only. Check DPS's current instructions before you schedule anything; they always win.
This page is a reference, not a lesson. It assumes you already know the overall licensing path, which our Texas CDL process guide covers. What follows is the vocabulary grouped the way the test groups it, with a one-line definition for each term and the document the term comes from.
Learn each noun with the verb that follows it. The test almost never asks "what is a slack adjuster"; it asks what you check on one. In the model CDL manual the pairs are consistent: you check slack adjusters, you connect glad hands, you drain air tanks, you chock wheels. If you memorize the noun alone you will recognize the question and still miss the answer.
Pay as much attention to the answer choices as to the question. Distractors are built out of near-synonyms that mean different things in this trade: loose and secure, worn and cracked, leaking and low. A candidate who reads English slowly tends to spend all their time on the question stem and then guess among four options they never fully parsed.
The roadside version of this test is different again. FMCSA describes its English language proficiency assessment as two steps: a driver interview, to see whether you can respond sufficiently to official inquiries, and then, if you pass that step, a highway traffic sign recognition assessment. That second half is why the sign vocabulary in the Texas handbook is worth studying even though it feels like beginner material.
If you want the pre-trip parts drilled with pictures rather than word lists, the illustrated inspection chapter in our Texas CDL study guide names each part on the diagram in the same words the examiner uses.
Air brakes: brakes that use compressed air instead of hydraulic fluid. The model CDL manual describes them as three systems in one vehicle: the service brake, the parking brake, and the emergency brake. Air compressor: the pump that fills the tanks. Governor: the device that decides when the compressor pumps, cutting out at around 125 psi and cutting back in at around 100 psi in the manual's example figures, with the manufacturer's specification controlling on any given vehicle. Air storage tanks: the reservoirs that hold the compressed air. Air tank drains: the valves at the bottom, because water and compressor oil collect there and water can freeze.
Slack adjuster: the linkage between the brake chamber pushrod and the brake itself. Pushrod stroke: how far that rod travels when the brakes are applied; 49 CFR 393.47 sets a maximum stroke by chamber type, and requires that the effective length of the slack adjuster on each end of an axle be the same. Tractor protection valve: the valve that closes automatically when air pressure drops into roughly the 20 to 45 psi range, keeping air in the tractor.
Glad hands: the coupling devices that connect the service and emergency air lines from the tractor to the trailer, sealed with rubber seals you clean before coupling. Fifth wheel: the coupling plate on the back of the tractor, with jaws that close around the trailer's pin. Kingpin: that pin, on the front underside of the trailer, which you check is not bent or broken before coupling. Landing gear: the trailer's front support legs, which you crank down before uncoupling.
This is the group most often underestimated. The words are ordinary English, but the inspection uses them narrowly, and 49 CFR 383.113(a) requires that a skills test applicant be able to identify each safety-related part and explain what to look for.
Leak: anything escaping that should stay inside, whether air, oil, coolant, fuel, or grease. The manual's air leakage check is a timed pressure drop, so "leak" can mean a number on a gauge rather than a visible drip. Cracked: split, in metal, glass, or rubber, most often used about the frame, mounts, hoses, and mirrors. Frayed: worn through at the edges, used about seat belts and webbing, where the manual's phrase is "not ripped or frayed."
Secure and securely mounted: fastened so the part cannot move, the phrase that repeats through the manual's inspection lists. Loose is its opposite and is a defect, not a description. Missing or damaged: parts absent or broken. Worn: reduced by use, used mostly about tire tread and brake linings. Chocked: blocked with wedges against the wheels so the vehicle cannot roll.
Out of adjustment: the brake condition where pushrod stroke has passed the legal limit in 393.47. The model manual states plainly that out-of-adjustment brakes are the most common problem found in roadside inspections, and warns that manually adjusting an automatic slack adjuster to bring stroke back within limits usually masks a mechanical problem rather than fixing it.
Hydroplaning: the loss of tire contact with the road when water or slush collects on it, leaving little or no traction. The manual notes it can occur at speeds as low as 30 mph if there is a lot of water, and is more likely with low tire pressure or worn tread. The recovery it teaches is to release the accelerator and push in the clutch, not to brake.
Jackknife: the folding of a tractor and trailer toward each other at a sharp angle. A tractor jackknife starts with the drive wheels; a trailer jackknife is the trailer swinging out to the side. Bobtail: a tractor driven without a semitrailer attached. The manual is specific that bobtails are hard to stop smoothly and take longer to stop than a tractor-semitrailer loaded to maximum gross weight, which is the opposite of what most people assume.
Escape ramp: a lane built beside steep mountain downgrades, using a long bed of loose, soft material, sometimes with an upgrade, to stop a runaway vehicle. Retarder: a device that helps slow the vehicle and save brake wear; the manual names exhaust, engine, hydraulic, and electric types, and warns to turn retarders off when the road is slippery because they can cause the drive wheels to skid.
Tandem: two axles set close together. On a semitrailer the tandem often slides forward and back to shift weight, held by locking pins that appear on the pre-trip inspection as the tandem release arm and locking pins. Related words worth knowing cold: downgrade, runaway, skid, and counter-steer, meaning to turn the wheel back the other way after an evasive move.
Endorsement: defined in 49 CFR 383.5 as "an authorization to an individual's CLP or CDL required to permit the individual to operate certain types of commercial motor vehicles." The codes in 383.153 are T for double and triple trailers, P for passenger, N for tank vehicle, H for hazardous materials, X for tank and hazmat together, and S for school bus. Restriction: the mirror image, a limit on what you may drive. It is not defined in the 383.5 definitions section, but 383.153 lists the codes: L, no air brake equipped CMV; Z, no full air brake equipped CMV; E, no manual transmission; O, no tractor-trailer; M, no Class A passenger vehicle; N, no Class A and B passenger vehicle; K, intrastate only; V, medical variance. Note that N appears in both lists with different meanings, so read the column, not just the letter.
Out-of-service order: 383.5 defines it as a declaration by an authorized enforcement officer of a federal, state, Canadian, Mexican, or local jurisdiction that a driver, a vehicle, or a carrier operation is out of service. On the vehicle side, 49 CFR 396.9 requires authorized personnel to declare and mark out of service any vehicle whose mechanical condition or loading would likely cause an accident or breakdown, and prohibits anyone from operating it until all repairs required by the notice are completed.
Placard: the diamond-shaped hazard sign on a hazmat load. Under 49 CFR 172.504(a), each bulk packaging, freight container, unit load device, transport vehicle, or rail car containing hazardous material must be placarded on each side and each end. Shipping paper: the document describing the hazardous material, required of the person who offers it for transport under 172.200(a). Manifest is a narrower word than most candidates think. In the hazardous materials regulations it refers specifically to the EPA hazardous waste manifest, Form 8700-22, required by 172.205 and carried during transportation the same way shipping papers are. Tank vehicle: 383.5 defines it by capacity, a vehicle designed to carry liquid or gas in a tank with an individual rated capacity over 119 gallons and an aggregate rated capacity of 1,000 gallons or more.
Hours of service: the driving and duty limits in 49 CFR Part 395. On-duty time is defined in 395.2 as all time from when a driver begins work or is required to be in readiness to work until relieved from work and all responsibility for performing work, which is why loading, fueling, and waiting count. For property-carrying drivers, 395.3 sets 11 hours of driving after 10 consecutive hours off duty, a 14-hour window after coming on duty, a required 30-minute interruption before more than 8 hours of driving time have passed, and a 60-hour limit in 7 days or 70 in 8 depending on whether the carrier operates every day.
Texas DPS has announced that it administers CDL and CLP knowledge tests in English only, aligning with the federal English language proficiency requirement. We were not able to load the DPS page directly while researching this guide, so confirm the current policy and its effective date on the Texas DPS commercial driver license pages before you schedule a test.
Reporting on the DPS announcement says interpreters are not permitted for CDL knowledge or skills testing, and that applicants must understand and respond to a skills test examiner's verbal instructions in English. Because we could not read the DPS policy page itself, treat that as a strong signal to verify rather than as our confirmed statement. Ask DPS directly.
Yes, at roadside, with one exception that matters in Texas: under FMCSA's current enforcement guidance a driver whose trip stays inside a U.S.-Mexico border commercial zone is cited but not placed out of service. 49 CFR 391.11(b)(2) requires that a driver read and speak English sufficiently for the four purposes it lists, and since June 25, 2025 a violation has been an out-of-service violation under the North American Standard Out-of-Service Criteria. FMCSA proposed on August 10, 2026 to codify that consequence in the regulation itself; comments are open until October 9, 2026, and it is a proposal, not a final rule.
An endorsement adds authority: it permits you to operate a type of vehicle you otherwise could not, such as a tank vehicle or a school bus. A restriction removes authority: it records something you may not do, such as drive a CMV with full air brakes. Both appear on the license as single letters listed in 49 CFR 383.153, and the letter N is used in both lists with different meanings.
For the pre-trip inspection, effectively yes. 49 CFR 383.113(a) requires an applicant to identify each safety-related part on the vehicle and explain what to look for. Knowing the part in your first language is not enough; you need the English name and the English defect word that goes with it.
Rules change. Where a figure or a procedure can move, the issuing agency’s current published instructions win over anything here.
