Why are doubles and triples combinations more likely to roll over than single-trailer combinations in the same turn?

ROLLOVER RISK IN DOUBLES AND TRIPLES is substantially higher than in single-trailer combinations because of rearward amplification — each articulation point increases the lateral force experienced by the next unit in the chain.

Physics: When a combination vehicle goes through a curve, centrifugal force acts on each unit. In a single tractor-semitrailer, the force is shared and controlled through one articulation. In a doubles combination, the second trailer's converter dolly introduces a second pivot point that can allow the second trailer to respond more aggressively to steering inputs.

Result: A moderate curve that a single-trailer would handle at highway speed could roll the second trailer in a doubles at the same speed.

Statistics: Doubles and triples have a significantly higher rollover rate per million miles than single-trailer combinations.

Safe speed adjustment: Reduce speed in curves far below what would feel necessary in a single-trailer; what 'feels' stable in the tractor may not be stable for the last trailer — mirrors cannot always detect the early stages of rear trailer sway until it is too late; the target is a curve entry speed conservative enough that the last trailer never approaches its rollover threshold.