Frontal restraint systems are currently designed to optimise the protection afforded to 50th percentile car occupants in one particular impact type at one particular speed, largely because of regulatory testing. The purpose of this work was to investigate active adaptive systems for vehicle occupants of different sizes and to quantify the benefits. A variety of active adaptive systems were evaluated in computer simulation using discrete and scaleable dummies and in tests on a sled rig using 5th, 50th and 95th percentile discrete dummies. The restraint system characteristics studied parametrically included:​ seat belt anchor height, pre-tensioner stroke and load, load limiter maximum force, airbag size and vent area, out of position occupant and a moving seat concept. The results indicated that adaptive systems can provide substantial benefits but disadvantages can also be introduced if the system is not properly optimised and tested. A moving seat concept was shown to have the potential to reduce injury substantially to smaller occupants and in some out of position cases, especially when coupled with occupant sensing and collision prediction.