Integrity applied to cars

To transfer the statistics-based integrity approach from aircraft to cars, the horizontal alert and protection levels around the test car was stretched out from a circle to an elongated ‘lozenge’ shape, taking account of the fact that forwards and backwards collisions pose a greater risk than sideways collisions. The lengths and widths of these protection levels are guided by the local speed limit, with the overall safety level guided by the study of UK and European accident probabilities, aiming to maintain safety 99.999% of the time.