For occupants, Joksch (1993) found the probability of death for drivers in multi-vehicle accidents increased as the fourth power of impact speed Injuries are caused by sudden, severe acceleration (or deceleration); this is difficult to measure. For example, the elimination of head-on KSI crashes simply required the installation of an appropriate median crash barrier. Also, roundabouts, often with speed reducing approaches, encounter very few KSI crashes. Study conducted in Finland revealed that the fatality risk is increased most when a road accident type is either pedestrian or meeting of the vehicles. Interventions are generally much easier to identify in the modern road safety paradigm, whose focus is on the human tolerances for serious injury and death.
A comprehensive outline of interventions areas can be seen in management systems for road safety. The old road safety paradigm of purely crash risk is a far more complex matter. Contributing factors to highway crashes may be related to the driver the vehicle r the road itself Interventions may seek to reduce or compensate for these factors, or reduce the severity of crashes. In addition to management systems, which apply predominantly to networks in built-up areas, another class of interventions relates to the design of roadway networks for new districts. Such interventions explore the configurations of a network that will inherently reduce the probability of collisions. The autobahn fatality rate of 1.9 deaths per billion-travel-kilometres compared favorably with the 4.7 rate on urban streets and 6.6 rate on rural roads.
Interventions for the prevention of road traffic injuries are often evaluated; the Cochrane Library has published a wide variety of reviews of interventions for the prevention of road traffic injuries. A traffic circle applied to a four-way intersection as a means of improving its safety. This device, with a proven record of collision reductions and traffic flow improvement, turns the cross-intersection into four virtual three-way intersections. Most injuries occur on urban streets but most fatalities on rural roads, while motorways are the safest in relation to distance traveled. For example, in 2013, German autobahns carried 31% of motorized road traffic while accounting for 13% of Germany's traffic deaths. For road traffic safety purposes it can be helpful to classify roads into three usages: built-up urban streets with slower speeds, greater densities, and more diversity among road users; non built-up rural roads with higher speeds; and major highways reserved for motor-vehicles, and which are often designed to minimize and attenuate crashes.
Though not strictly a traffic calming measure, mini-traffic circles implanted in normal intersections of neighborhood streets have been shown to reduce collisions at intersections dramatically. For planned neighborhoods, studies recommend new network configurations, such as the Fused Grid or 3-Way Offset. These layout models organize a neighbourhood area as a zone of no cut-through traffic by means of loops or dead-end streets. On neighborhood roads where many vulnerable road users, such as pedestrians and bicyclists can be found, traffic calming can be a tool for road safety. Shared space schemes, which rely on human instincts and interactions, such as eye contact, for their effectiveness.