This paper starts with a review of accident situations requiring underrun bumpers and sideguards. Bumper design features discussed include height aboveground, strength, travel, and force-deflection characteristics. A joint programme between the Transport and Road Research Laboratory (TRRL) and TI Tube Products Ltd. is described for the design and development of a front underrun bumper using the plastic deformation of mild steel tubes to absorb energy, and results of car-to-truck front impact are summarised. The final design is able to protect seatbelted car occupants from intrusion from a frontal collision at a closing speed of 65km/h. for a totai bumper weight of approximately 60kg. it is recommended that any future legislation for front underrun guards require an energy-absorption capability, and a possible legislative test procedure is outlined.Tests carried out on sideguards fitted to an articulated goods vehicle, using a simulated pedal cycle accident, are described. It was found that the incidence of running over of the cyclist could be reduced to 40 percent of the test runs by using a guard that just met the United Kingdom legal requirements. An improved guard with lower ground clearance reduced the incidence to near zero. Better performance in other respects was obtained by making the guard flush with the side of the semitrailer and by extending the sideguard longitudinally, nearer to the trailer wheels and closer to the tractor.