The crash performance of emergency locking retractor (inertia reel) seat belts is examined by in-depth field investigations and by laboratory simulations. It is found that the inclusion of the retractor increases body excursions for the wearer of a lap/sash seat belt. The increase is not excessive and in general, crash performance is found to be satisfactory. The Australian Design Rule requirements for emergency locking retractor seat belts are examined and a number of efficiencies are discussed. It is concluded that a revised dynamic test is required, based on the limitation of excursions of a specific validated anthropomorphic dummy.