In the 1950s up to 8,000 people died every year on the roads in this country - a truly horrific figure. Thankfully it has now fallen to around 2,000 a year - still a terrible toll, but a vast improvement, particularly given the increase in cars on the road. Dallas Campbell looks back over decades of Horizon and BBC archive to chart the key scientific breakthroughs that have transformed road safety and saved millions of lives. However, it hasn't all been about innovative engineering and groundbreaking medical discoveries - scientists have also had to act as campaigners, persuading car manufacturers to install their life saving devices and urging the public to use them.