Texas Tank Vehicle Study Guide
This page covers the Tank Vehicle portion of the CDL exam as administered by the Texas Department of Public Safety in Texas. The endorsement code is N. Below you'll find what's tested, focused study notes, and a direct link to a 25-question Texas-specific practice test.
Take the TX Tank Vehicle Practice Test →
What's on the test
- Smooth-bore (unbaffled), baffled, and compartmented tanks
- Liquid surge and how it affects handling
- Outage (the empty space left for expansion)
- Center of gravity and rollover risk
- Loading, unloading, bonding and grounding for flammable liquids
- Driving techniques unique to tankers (slow lane changes, gentle braking)
- Special inspection items (tank shell, manhole covers, vapor recovery)
- Hazmat overlap when carrying placarded liquids
Study notes
Smooth-bore is the worst surge.
A smooth-bore tank has no internal baffles, so liquid sloshes back and forth freely along the entire length of the tank. The forward surge after a stop can push a fully stopped tanker out into an intersection. Always leave more space and brake earlier with a smooth-bore tank.
Always leave outage.
Liquids expand when warm. Federal rules require that the shipper leave a small percentage of the tank empty (the "outage") to accommodate this expansion. The exact amount varies by product, but the test concept is constant: never load to 100% of the tank's capacity unless the product is specifically allowed to be loaded full.
Bond and ground for flammable loading.
When loading or unloading a flammable liquid, you connect a bonding cable from the truck to the loading equipment first, before opening the manhole or starting the pump. This prevents a static-electricity spark from igniting vapor.
Curve speeds are not your friend.
Posted curve and ramp speeds are calibrated for cars. A loaded tanker should take curves at least 5 mph below the posted speed, and slow even more on cloverleaf ramps where the curve tightens.
Stop and re-check inspection items.
After about the first 25 miles of a trip, a tanker driver should pull over and re-check tires, cargo, and securement. Heat, vibration, and load shift can loosen things that were tight in the yard. This is a classic CDL test question and the wrong answer is usually "only at the destination".
Texas-specific notes
In Texas, the Tank Vehicle knowledge exam is one of several written tests administered at Texas Department of Public Safety CDL testing offices. Most applicants take it on the same day as the General Knowledge test. The vocabulary and question style match the official Texas CDL handbook closely, which is why we recommend reading the relevant chapter of the handbook in addition to working through our practice tests. Pay particular attention to the chapter's "key terms" sidebars — those are almost always the source of vocabulary-style multiple-choice questions on the real exam.
If your test vehicle is equipped with air brakes, you must additionally pass the Air Brakes knowledge test or the air-brake portion will be removed from your license as an L-restriction. The skills test (vehicle inspection, basic control, and on-road) is administered by Texas Department of Public Safety examiners or by approved third-party testers. Bring your CLP, your medical certificate, and proof of insurance for the test vehicle.
A handful of Texas-specific quirks worth knowing: the office may require a separate appointment for the skills test versus the knowledge test; many Texas testing offices do not allow rental commercial vehicles for the skills test; and you generally need to wait at least one business day between failed attempts on the same knowledge exam (your office may extend that further on subsequent failures).
Test-day strategy
Read every question twice. CDL exam writers love to insert a single qualifier — "always," "never," "only," "primary" — that flips the right answer. When two answers look almost identical, pay attention to the verb (is it "must," "should," or "may"?), and to any numbers (14 days, 100 air miles, 8 hours). On endorsement tests in particular, watch for trick framing where a true statement about a different endorsement is offered as the "correct" answer.
Don't second-guess yourself. Your first instinct is correct on roughly 70% of CDL knowledge questions, and changes most often turn a right answer into a wrong one. Mark the questions you're unsure of, finish the rest of the exam quickly, then go back and reconsider only the marked questions with the time you have left.