The Physics of Tractor-Trailer Tanker Driving and the Art of Keeping Right-Side Up

The Physics of Tractor-Trailer Tanker Driving and the Art of Keeping Right-Side Up  (or, as we  truckers like to say: “Keeping the shiny side up and the rubber side down”)

“You can go down a mountain – or into a curve – too slow a million times with no problems. But go down that same mountain – or into that same curve – too fast just once and that will be your last time.” ~ Trucker

“We just put Sir Isaac Newton in the driver’s seat” ~ Tom Hanks (as Jim Lovell in Apollo 13)

Well, I begin my new job on Monday: Tanker Driver. I like science, especially physics, and driving a tractor-trailer has always been somewhat of a physics examination for me.  After all, when you think about it, driving a tractor-trailer up, over, and down packed snow and ice covered mountain roads, for example, is ALL about physics, isn’t it? And the driver keeping the truck on the road, and himself alive, which is always my aim. Tricky with my new job, though. Challenging, for me, I suppose, which is always good, because I hate being bored! LOL :) [Update: I only lasted two weeks on this job. My mind wasn't together enough for all that and everything else too. Too much stress. Like driving on eggshells, too, to me. I'm too distracted/distractible for that. I'm afraid I'd kill somebody, or myself. My hat's off to those guys.]

Modern Theoretical Physics is stuff like string “theory”, quantum gravity, dark matter, and stuff like that. See:

Applied Newtonian Physics (not to be confused with Modified Newtonian Dynamics) would be stuff like: constructing bridges, going to the moon, and driving heavy class 8 trucks with liquid bulk tank semi-trailers attached to them.

Theoretical physicist Michio Kaku probably doesn’t care about this outdated Newtonian stuff, but I certainly do, because my life – and the lives of others – depends upon it. For example, whenever truckers haul liquid bulk tankers the liquid cargo they carry is always in motion, which, considering all the places such trucks go and all the traffic they go through in order to get where they’re going, makes for some very complex dynamics and, as a driver, I need to drive accordingly. “Accordingly” as in: “According to Isaac Newton”, and not according to Albert Einstein. (Regarding my take on physics, time, Newton, and Einstein, see my book (beginning at page 101) here)

“Fluid Dynamics in a Tractor-Trailer Tank Trailer: A comprehensive directional dynamics model of a tractor-tank trailer is developed by integrating a non-linear dynamic fluid slosh model to the three-dimensional vehicle dynamics model. The nonlinear fluid slosh equations are solved in an Eulerian mesh to determine dynamic fluid slosh loads caused by the dynamic motion of the vehicle. The dynamic fluid slosh forces and moments are coupled with the vehicle dynamics model to study the directional response characteristics of tank vehicles. The directional response characteristics of partially filled tank vehicles employing dynamic slosh model are compared to those employing quasi-dynamic vehicle model, for steady as well as transient directional maneuvers. Simulation results reveal that during a steady steer maneuver, the dynamic fluid slosh loads introduce oscillatory directional response about a steady-state value calculated from the quasi-dynamic vehicle model. The directional response characteristics obtained using the quasi-dynamic and dynamic fluid slosh models during transient steer inputs show good correlation. Based on this study, it can be concluded that the quasi-dynamic model can predict the directional response characteristics of tank vehicles quite close to that evaluated using the comprehensive fluid slosh model.”


“Simulation of Dynamic Rollover Threshold for Heavy Trucks” See:

“The transient forces and roll moment caused by fluid slosh within partly filled circular and conical cross-section tanks, subject to a time-varying lateral acceleration field, are evaluated numerically and compared with those estimated from a quasi-static formulation. The variations in the centre of mass coordinates, vertical and lateral forces and roll moment are applied to the roll-moment model of a 6-axle tractor-semi-trailer articulated tank vehicle for analysis of the steady-turning rollover threshold. The results show that the magnitudes of transient lateral force and roll moment approach significantly higher values, than those estimated from the quasi-static formulations. The mean values of the force and moment, however, are similar to those predicted from the quasi-static solution. The steady-turning rollover-threshold accelerations of the vehicle combination with partly filled tanks are thus considerably lower when transient slosh forces and moment are considered in the moment equilibrium, specifically for the intermediate fill volumes. The results further show that the static roll stability limits of the combination with a conical cross-section tank are considerably higher than that with a circular cross-section tank.”


“The truck driver’s excessive, rapid, evasive steering maneuver triggered a sequence of events that caused the cargo tank semitrailer to roll over, decouple from the truck-tractor, penetrate a steel W-beam guardrail, and collide with a bridge footing and concrete pier column supporting the southbound I-465 overpass.”

See: NTSB Safety Recommendation for cargo tank heavy vehicles at

USDOT “Concept of Operations and Voluntary Operational Requirements for Vehicular Stability Systems (VSS) On-board Commercial Motor Vehicles”


Tire Condition and Pressure

Regular tire maintenance is an important component of preventing tanker truck rollovers. Checking the tires regularly for even wear and damage and ensuring the correct level of air pressure in all tires on the rig can greatly reduce tipping of these types of vehicles. Preventing blowouts or unexpected handling problems due to tire failure decreases the risk of rollovers, especially considering the already more difficult than average handling of tanker trucks.

Speed and Control

Slowing down, especially in places where hazards exist, helps drivers maintain control of their tanker trucks and prevent rollover accidents. Ice or water on the roadway can cause slippage or hydroplaning that greatly increases the potential for a rollover.

Approaching areas where this is a concern at a lower speed will improve the handling of the truck and make the driver less likely to experience loss of control. The driver should also take into account the unpredictability of other drivers on the road.

Inattentive drivers often fail to yield the right of way, and many of them drive above the speed limits regularly. Even if the tanker is an emergency vehicle headed to a fire, it is no guarantee that the driving public will properly yield to the oncoming tanker.


According to the Centers for Disease Control, tanker truck drivers should participate in ongoing driver training and take refresher courses at least twice a year. This will remind them of the vehicle’s capabilities and limitations as well as keep them current with training.

Weight Distribution

Weight distribution is an important factor in preventing rollover crashes in tanker trucks. The sloshing of liquid inside the tanker can be a powerful force that can shift the truck’s center of gravity and cause a rollover in some cases. Always check to be sure that weight in the tank, as well as the front and rear of the vehicle, is distributed evenly. Fill water tanks to appropriate capacities and do not exceed the gross axle weight recommended for the chassis.

Read more: Safety Tips to Reduce Tanker Truck Rollover Crashes |

RUHL Forensics: “Rollovers of Commercial Vehicles” See:

“An Assessment of Tank Truck Roll Stability” See:

9h30-10h00: “Safety Dynamics of Partly-Filled Road Tankers” – Subhash Rakheja, CONCAVE Research Center, Concordia University, Canada.

Abstract: Large amplitude slosh can be induced within a partly-filled road tank vehicle under mild to severe directional manoeuvres leading to additional stresses on the container, and reduced vehicle stability and control limits. The magnitudes of slosh-induced forces and moments depend upon a number of tank design factors such as tank cross-section, baffles and fill volume, apart from various operating factors. In this presentation, the role of tank design factors on the steady-state and transient fluid slosh are highlighted through analysis of three-dimensional models of the partly-filled tanks.

The steady-state fluid slosh model is applied to derive the dynamic response and stability characteristics of a partly-filled articulated liquid cargo vehicle with tanks of arbitrary cross-section under steering and braking-in-a-turn maneuvers. The directional dynamic characteristics under a braking-in-a- turn maneuver are evaluated in terms of moments induced by the moving cargo, wheel dynamic load factor, load transfer ratio, yaw and roll response, and braking performance of the vehicle. An alternate “Reuleaux triangular” tank cross-section is suggested to minimize the slosh loads in the roll plane.

The results of the study reveal that a partly-filled articulated tank vehicle, subject to braking-in-a-turn, is more susceptible to rollover on dry roads, while it exhibits a higher propensity of trailer swing on slippery roads. A three-dimensional computational fluid dynamic slosh model of the tank is further presented for analysis of forces and moments caused by transient fluid slosh. A comprehensive experiment is designed to study fluid slosh within a scale model tank with and without the baffles under continuous as well as single-cycle sinusoidal lateral and longitudinal acceleration excitations. The measured data are used to examine the validity of the fluid slosh model in terms of the slosh natural frequencies, and three-dimensional components of slosh forces and moments.

The fluid slosh characteristics are analyzed considering a full-size tank under different fill volumes corresponding to a constant load and excitations representing steady- turning, straight-line braking, braking-in-turn and path change maneuvers. The fluid slosh analyses are also carried out to explore the anti-slosh effectiveness of different designs of transverse baffles such as full, partial, single and multiple orifices, oblique and an alternating baffles arrangement.

The influences of transient fluid slosh on tank vehicle safety dynamics are studied by incorporating fluid slosh model to an in-plane vehicle model. The roll stability analyses are performed for circular and “Reuleaux triangular” tanks under conditions of constant and variable cargo loads. The results attained are compared with the quasi-static solutions to demonstrate the role of transient slosh loads on the roll stability limits. The three- dimensional slosh model of a partly-filled tank with and without baffles is also integrated to a 7-DOF pitch plane model of a tridem truck to analyze its straight-line braking characteristics in the presence of fluid slosh. A degradation of the braking performance of the partly filled tank truck was evident in the presence of transient fluid slosh, particularly in the absence of baffles. The braking performance, however, is highly dependent upon fill volume, presence of baffles, and severity of the braking input.

For a clean-bore tank truck, the stopping distance increases monotonically with decreasing fill volume, while the addition of transverse baffles in general results in considerably shorter stopping distance. Although the analyses are limited to conventional single-orifice baffles, the proposed coupled vehicle–tank model could serve as an important tool for exploring alternative baffle designs and layouts.

Under sharp turn condition, side tumbling of tanker semi-trailer often happens. Aiming at dangerous accidents of this kind, in this paper, the ALE (Arbitrary Lagrange-Euler) method is employed to analyze the process of tanker semi-trailer during sharp turn. Under different liquid filling ratio, liquid sloshing influence on the steering stability is analyzed. Obtained the Y-direction force of some units located at middle of tank’s left side, the Y-direction acceleration and the Z-direction displacement of the key nodes at the right side of the tank. The results were significance for tanker semi-trailer’s steering stability simulation.”

“The Study of Tanker Semi-trailer’s Steering Stability on the Fluid-Structure Interaction“



Analysis of large truck rollover crashes – “The Large Truck Crash Causation Study” undertaken by the Federal Motor Carrier Safety Administration describes 239 crashes in which a truck rolled over. In-depth analysis revealed almost half resulted from failing to adjust speed to curves in the road, (mostly on-and off-ramps), the load being carried, condition of the brakes, road surface, and intersection conditions. A second major crash contributor involved attention: simply being inattentive, dozing or falling asleep, and distraction, all leading to situations where a sudden direction change resulted in a rollover. The third large crash contributor involved steering: over-steering to the point of rolling over, not steering enough to stay in lane, and overcorrecting to the point of having to counter-steer to remain on the road. Finally, loads are a frequent problem when drivers fail to take account of their weight, height or security, or when loading takes place before they are assigned. Instruction in rollover prevention, like most truck driver training, comes through printed publications.”


VIDEO – USDOT Cargo Tank Driver Rollover Prevention Video (also download here).

VIDEO – USDOT ROLL – CRASH – Tractor Trailer Combination

“You can go down a mountain – or into a curve – too slow a million times with no problems. But go down that same mountain – or into that same curve – too fast just once and that will be your last time.”

LCL Bulk Transport – Green Bay, Wisconsin
“Keeping the shiny side up and the rubber side down.”

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About ajmacdonaldjr

writer, author, blogger
This entry was posted in Accident Prevention, Science and tagged , , , , , , , , , , , , , , , , , . Bookmark the permalink.

3 Responses to The Physics of Tractor-Trailer Tanker Driving and the Art of Keeping Right-Side Up

  1. Anonymous says:

    Nice advice

    • Please search http://WWW.DEFORMABLE KINGPIN.COM that explains a simple to understand
      solution to forbid a Tractor to follow to It’s destruction during rollover accidents. The concept
      is the same as to why you have fuses or circuit breakers in electrical systems in your home,
      office or car — a failsafe — to prevent further destruction. This innovation is a simple modification
      of a component, the Trailer’s coupling kingpin, whose design has been a standard for over 70
      years, which can be made to deform and not allow an extremely stable Tractor to follow
      to destruction when the Trailer, that is the dominant controlling force, is in IMMINENT peril
      for rollover, that includes also blown over Tractor Trailers.
      The NHTSA & FMCSA continue to turn their backs and ignore their past funded research
      conclusions, as the trucking industry evolves greater unstable Tractor Trailers on our
      highways that have a primary attribute for increasing payload capacity. These catastrophes
      will continue to occur in thousands of accidents of this type each year as they have in the
      past, and continue to cause infrastructure damage, that does harm and kills many hundreds of
      Tractor occupants annually. These combination vehicles are incendiary bombs when
      carrying flammable material in Tankers, and the flash point for these fires starts with the
      Tractor’s involvement. A statement received from the FMCSA states “There are a variety
      of technologies for preventing rollover crashes and we believe motor carriers should have
      as much flexibility as possible in selecting technologies to prevent crashes.” Clearly the
      fox is allowed to guard the hen house!!! The harm, death & destruction will continue with
      commercial combination vehicle rollover accidents. Donald J. Kaleta

  2. Tarah says:

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