Serious accidents and deaths on the roads of Britain have been greatly reduced over the last 20 years -- not because we are safer drivers but because of better safety engineering. Seat belts, airbags and crumple zones have all contributed to this decline. However, as Donal McNally from the University of Nottingham explains, it is very difficult to protect the body from the huge increase in the forces impacting upon it in an accident. The second most likely cause of death in a car accident is something called an "aortic rupture" and it remains a mystery. Under increased pressure the aorta always ruptures in the same place but no one knows exactly why. Like any good scientists or research engineer Donal is keen to test a particular hypothesis using real world simulations to discover the cause of aortic ruptures. Can he find the answer or will his hypothesis be disproved? This film is part of a project funded by the Royal Academy of Engineering to develop the on camera communication skills of engineers across the UK. The Ri is on Twitter: http://twitter.com/ri_science and Facebook: http://www.facebook.com/royalinstitution and Tumblr: http://ri-science.tumblr.com/ Our editorial policy: http://www.rigb.org/home/editorial-policy Subscribe for the latest science videos: http://bit.ly/RiNewsletter