Tanker: Tanker Handling
12 questions in the bank cover this topic. Everything below is drawn from the sources those questions cite.
Sources: 49 CFR 177.816, 49 CFR 392.10, TC 21-305-20 para 13-15, TC 21-305-20 para 3-37, TC 21-305-20 para 3-52
What you need to know
Releasing the brakes restores wheel rotation, and a rolling wheel can generate the sideways grip that pulls the trailer back in line.
A high center of gravity makes a tank less forgiving, so the window is short.
Semitrailer jackknifing occurs when the semitrailer wheels lock and skid to the left or right. Control must be regained immediately if it is to be regained at all. To regain control, quickly release the brakes to get the wheels turning.
TC 21-305-20 para 13-15
The manual notes centrifugal force tends to tip over large vehicles on curves, not only skid them.
A tank's load sits high and, in a partly filled tank, can also move, so the tipping point arrives before the sliding point. A tank carries its load high, so the force acts on a tall mass and rollover can come before any skid.
Whenever centrifugal force is greater than friction, the vehicle will skid. Centrifugal force also tends to tip overlarge vehicles on curves.
TC 21-305-20 para 3-37
Speed is chosen before entry.
In a tank this matters doubly, because braking or steering hard once in the curve can start liquid moving inside the shell and the load then works against you.
Driving slowly into a curve is the only way to prevent skidding.
TC 21-305-20 para 3-52
392.10 gives a window, not just a minimum: no closer than 15 feet and no further than 50.
Too close and you cannot see down the track, too far and you cannot judge the crossing. Then look and listen both ways before crossing.
Stops the commercial motor vehicle within 50 feet of, and not closer than 15 feet to, the tracks; thereafter listens and looks in each direction along the tracks for an approaching train; and ascertains that no train is approaching.
49 CFR 392.10
Pick the gear before you move and hold it.
A missed shift on the tracks leaves you stalled across them, which is the one place a stall is unsurvivable.
When it is safe to do so, the driver may drive the commercial motor vehicle across the tracks in a gear that permits the commercial motor vehicle to complete the crossing without a change of gears. The driver must not shift gears while crossing the tracks.
49 CFR 392.10
392.10(a) lists buses with passengers, chlorine loads and poison gas placards among the vehicles that must stop.
The common thread is that the consequence of being hit is catastrophic rather than merely serious.
Every bus transporting passengers,
49 CFR 392.10
The rule asks you to ascertain, not merely glance.
Listening matters because a train can be hidden by a curve or a building while still being plainly audible. You must also satisfy yourself that no train is coming.
listens and looks in each direction along the tracks for an approaching train; and ascertains that no train is approaching
49 CFR 392.10
The regulation lists all of them together, plus the effect of partial loads.
They compound: a partly filled tank has both the worst surge and a center of gravity that moves with it.
Special vehicle handling characteristics, including: high center of gravity, fluid-load subject to surge, effects of fluid-load surge on braking, characteristic differences in stability among baffled, unbaffled, and multi-compartmented tanks; and effects of partial loads on vehicle stability;
49 CFR 177.816
A full tank has nowhere to move and an empty one has nothing to move.
A partial load has both room and mass, which is why the rule names the effects of partial loads specifically. Surge and a shifting center of gravity then act together.
Special vehicle handling characteristics, including: high center of gravity, fluid-load subject to surge, effects of fluid-load surge on braking, characteristic differences in stability among baffled, unbaffled, and multi-compartmented tanks; and effects of partial loads on vehicle stability;
49 CFR 177.816
The regulation names the effect on braking explicitly.
As you stop, the load runs forward, then rebounds and shoves the vehicle on again after you thought you had stopped.
Special vehicle handling characteristics, including: high center of gravity, fluid-load subject to surge, effects of fluid-load surge on braking, characteristic differences in stability among baffled, unbaffled, and multi-compartmented tanks; and effects of partial loads on vehicle stability;
49 CFR 177.816
Those three categories, by name.
The difference is how much freedom the liquid has to move, which is the only thing that makes one tank handle differently from another of the same size.
Special vehicle handling characteristics, including: high center of gravity, fluid-load subject to surge, effects of fluid-load surge on braking, characteristic differences in stability among baffled, unbaffled, and multi-compartmented tanks; and effects of partial loads on vehicle stability;
49 CFR 177.816
A tank carries its mass high by the shape of the vessel, so less lateral force is needed to tip it.
Combine that with a surging load and the force arrives suddenly rather than gradually.
Special vehicle handling characteristics, including: high center of gravity, fluid-load subject to surge, effects of fluid-load surge on braking, characteristic differences in stability among baffled, unbaffled, and multi-compartmented tanks; and effects of partial loads on vehicle stability;
49 CFR 177.816
Check yourself
- How do you respond when your tank trailer wheels lock and it swings?
- Why is a loaded tank especially vulnerable on a curve?
- The stated way to prevent a skid on a curve is ______.
- How should you handle a railroad crossing while hauling chlorine?
- How do you cross the tracks once you have stopped and it is clear?
- What must stop at every railroad crossing?
- You have stopped at the crossing. What does the regulation require before you move?
- What handling characteristics must cargo tank driver training cover?
- Your tank is half full. Why is that worse than full or empty?
- What does fluid-load surge do to your braking?
- What three tank types does the regulation say differ in stability?
- Why does a high center of gravity matter on your cargo tank?
Answers are in the practice test for this topic.