If a tank truck begins to roll over, what should the driver do?

Once a rollover passes the point of recovery — typically when the inside wheels leave the ground — the driver has almost no ability to prevent the vehicle from going over. The dynamics happen in fractions of a second. This is why the FMCSA manual emphasizes that prevention is the only reliable defense: slow before curves, smooth inputs, conservative speed, proper loading. By the time the driver feels the vehicle starting to roll, the outcome is largely determined by physics. If you suspect a rollover is imminent (you feel the vehicle leaning hard or you hear the cargo or chassis stressing), reduce speed immediately and steer toward straight-line travel. But again — prevent the situation; do not plan to recover from it.