What forces can be tolerated the human body?
The tolerance of the human body to kinetic forces released in road traffic crashes is limited. Injury is broadly related to the amount of kinetic energy applied to the human frame. Biomechanical research reported over the years to international scientific conferences (e.g. IRCOBI, STAPP, ESV) indicate that the relationship between crash forces and injury is known for a number of parts of the body and types of injury for different categories of road user as well as for different age groups. For example, a crash load applied to the chest of a young male may result in a bone fracture, but if applied to an elderly female, may produce a life-threatening injury. Whereas current vehicle crash protection is focused on the average-sized male occupant, the driving population is set to become more vulnerable to injury as it ages in line with general demographic trends.
The energy of a crash is related to the square of the velocity, so small increases in speed produce major increases in the risk of injury. The human tolerance to injury of a pedestrian hit by even the best-designed car will be exceeded if the vehicle is travelling at over 30km/h . Studies show that pedestrians have a 90% chance of surviving a car crash at 30km/h or below, but less than a 50% chance of surviving an impact at 45 km/h . Research shows that the probability of a pedestrian being killed rises by a factor of 8 as the impact speed of the car rises from 30km/h to 50km/h . The best-designed vehicle on the road today provides crash protection currently up to 70km/h for car occupants wearing seat belts in frontal impacts and 50 km/h in side impacts .
It has been estimated that the Swedish traffic system as a whole probably tolerates speeds of between 30 and 60 km/h, allows use on most roads between 50 and 100km/h (through road speed limits) and possibilities of use (by engine capability) to more than 200 km/h  Against this background, in the Swedish Vision Zero strategy, the amount of biomechanical energy to which people can be exposed without sustaining serious injury is now promoted as the basic road and vehicle design parameter. Sweden is re-shaping its road infrastructure and encouraging appropriate vehicle crash protection accordingly. A similar process is also underway in the Netherlands within the Dutch Sustainable Safety policy.