For most of our history, horseback was as fast as any human could hope to travel but then came along the industrial revolution which saw the birth of steam powered and internal combustion engines. Cars transformed our world they made travel easier, more accessible and faster than ever before.

This speed however also brought danger with it and for more than 60 years Horizon and the BBC have reported on how scientists and engineers have worked tirelessly to make road deaths a thing of the past. These scientists have often immersed themselves in controversial and disturbing research. In this documentary we chart the key scientific breakthroughs and the struggle to apply them to the real world.