Kinetic Energy Management, Haddon’s Matrix, and Road Safety

This paper is one of a series of ‘essential evidence’ papers which summarise key evidence from peer-reviewed literature which is used to strengthen the case for current transport policies and practice. All of the summaries are published on a single page on the Travelwest website in order to better disseminate academic research to practitioners for implementation within planning and policy.

Overview
Taking a system approach to road traffic injury prevention, road traffic injury is the result of energy transfer. Understanding the role of kinetic energy is important for all stakeholders in road traffic injury preventive activities.

In the concept of road traffic injury (RTI), mass and speed are properties of all the energy that can be transferred during a crash; and the two properties are connected to kinetic (mechanical) energy. The amount of energy interchange can result in injury severity that is equal to one half of the vehicle mass multiplied by the square of the vehicle speed. As researchers have noted, this means that the kinetic energy during a collision greatly increases due to velocity rather than mass and consequently, small increases in vehicle speed will result in major increases in the risk of injury.

Speed plays the most critical role in RTIs. In addition, the extent of bodily injury also depends on the shape of the objects involved and their rigidity as well as on what safety equipment is available. This is why kinetic energy management needs to focus more on speed, which can be an important implication in RTIs prevention. If a pedestrian is hit by a vehicle traveling at less than 30 km/h, the risk of bodily injury will be less than 10%, but this rises to about 50% if the vehicle is traveling at 45 km/h.

In the 1970s Haddon’s suggestion that injury prevention depended on controlling the agent—energy led him to develop strategies later applied to preventing RTIs. Haddon developed a two-dimensional matrix (The Haddon Matrix) to help conceptualize an injury event. This framework for analysis makes possible identification of factors related to the host, agent, and environment within the three phases before, during, and after the crash that might be explanatory and contribute to injury prevention strategies.