The Kinetic Energy Management Model (KEMM) was developed by MUARC as a conceptual model for defining and analysing the various factors influencing crash frequency and crash outcome severity. Five layers of “protection” are used to either prevent the crash (by deflecting energy) or mitigate its effects and limit the risk of serious injury to less than 10% (by absorbing energy). The KEMM concept is integrated with the four major risk areas in the Safe System: the human, the vehicle, the road and roadside, and system operation. In this study, the model was extended to analyse intersection crashes (model known as KEMM X) with the primary focus of better measuring the intrinsic safety of the intersection as a whole. The inner three layers of the KEMM-X, relating to the risk of serious injury or death, have been modelled mathematically to provide a tool for objectively quantifying the safety of individual conflicts within an intersection. Practical examples of risk reduction in each of the areas are provided.
Principles for safe intersection designs were then defined through the use of the model and are described in some detail in the body of the report:
- Fewer vehicles;
- Fewer intersections;
- Fewer conflict points per intersection;
- Impact speeds and impact angles constrained to biomechanically tolerable levels. i.e.,
a. For 90° collisions - impact (and, therefore, travel) speeds need to be less than 50km/h;
b. Where angle of impact can be somewhat reduced through layout design - impact speeds can be greater than 50 km/h but not greater than 70 km/h;
c. For conflicts between vehicles and unprotected road users (i.e. pedestrians, cyclists and motorcyclists), impact speeds should not exceed 30 km/h regardless of geometric layout, if pedestrian and cyclist risks of death are to remain below the nominated level of 10%;
d. Where the above speed and angle combinations cannot be met, crash risk must be reduced to a negligible level.