Many patents and devices exist which purport to prevent or inhibit “jackknifing” of tractor-semitrailer vehicles. The feasibility of such anti-jackknifing systems (AJS), specifically those which are located about the fifth wheel of tractor semitrailers was investigated.Through computer simulation the characteristics of jackknife and trailer swing were identified. Methods of controlling articulation in a jackknife generally produced favourable results. When the same AJS was applied to trailer swing conditions, the swing instability was usually increased rather than decreased. These results lead to the conclusion that efforts should be concentrated on devices for controlling or preventing a jackknife from occurring while maintaining a more or less neutral affect on swing.