CDL · Tank Vehicles · 5 min read
Making Smooth Stops and Turns
- Explain how a high center of gravity and liquid surge require exceptionally smooth starts, stops, turns, and lane changes.
- Apply safe braking practices, curve navigation procedures, and stopping distance principles to prevent rollovers and crashes.
- Identify the causes of skids and jackknifes, the actions required to restore traction, and the three factors that dictate liquid cargo loading.
Handling Surge and a High Center of Gravity
Operating a tank vehicle demands continuous concentration and specialized vehicle control. To drive tank vehicles safely, drivers must follow all safe driving rules that apply to commercial motor vehicles generally, while also accounting for the unique behavioral characteristics of liquid cargo. Two physical realities define how a tanker behaves on the road: tank vehicles have a high center of gravity, and the liquid cargo carried inside them is subject to surge. Liquid surge is the movement of liquid within the tank as the vehicle accelerates, slows down, stops, or turns.
Because of this high center of gravity and the presence of liquid surge, ordinary driving inputs can become dangerous if they are performed abruptly. Start very smoothly because a tank vehicle’s high center of gravity and liquid surge make abrupt movements hazardous. Similarly, due to a high center of gravity and liquid surge, drivers must slow down very smoothly. Slow down very smoothly to help control liquid surge.
The requirement for gentle, controlled control inputs extends to every maneuver. Due to a high center of gravity and liquid surge, drivers must stop very smoothly. Furthermore, tank vehicle drivers must make smooth turns and smooth lane changes. Jerking the steering wheel shifts the liquid cargo laterally, which raises the risk of losing control. By planning every maneuver well in advance, you can keep the liquid cargo as calm as possible and keep the vehicle stable.
Common mistakes
- Releasing the brakes too soon when coming to a stop can make it harder to control surge; keep steady pressure on the brakes.
- Assuming that posted curve advisory speeds are safe for tank vehicles, when in fact the posted speed for a curve may be too fast for a tanker's high center of gravity.
- Believing that an empty tanker stops faster than a loaded one, overlooking that empty tank vehicles may take longer to stop than full ones.
- Making abrupt steering adjustments while applying the brakes, which can cause a tank vehicle to roll over.
Key points
- To drive tank vehicles safely, drivers must follow all safe driving rules and account for liquid surge and a high center of gravity.
- Due to a high center of gravity and liquid surge, drivers must start, slow down, stop, turn, and change lanes very smoothly.
- Drivers must keep a steady pressure on the brakes and not release brake pressure too soon when coming to a stop to help control surge.
- Tank vehicle drivers must brake far in advance, increase following distance, and use controlled or stab braking (covered in Subsection 2.17.2) if a quick stop is needed to avoid a crash.
- Wet roads double the normal stopping distance, and empty tank vehicles may take longer to stop than full ones.
- Drivers must slow down before entering curves and accelerate slightly through, keeping in mind that posted curve speeds may be too fast for tank vehicles.
- Over steering, over accelerating, or over braking can cause skids; on tank trailers, drive wheel or trailer wheel skids can cause a jackknife, requiring immediate action to restore traction.
- The amount of liquid loaded depends on three factors: liquid expansion in transit, liquid weight, and legal weight limits; tanks may often be only partially filled with heavy liquids like some acids to avoid exceeding legal weight limits.
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