Current Definitions

The definitions of crash compatibility are reviewed in three literature groups:

3 This chapter is taken in part from an article [113] published in VDI Conference Vehicle Safety 2015. This article was prepared by Sadeghipour (main author) during his work. For more information, refer to the author’s contributions [113, p. 33].

1. Works before 2000, which tried to form a common understanding of crash compatibility as this topic was introduced and raised.

2. European research projects, which tried to develop an assessment approach for crash compatibility and implement it in safety regulations.

3. Individual researchers who supported the European research projects or criticized their works.

3.1.1.1 Before 2000

The term compatibility had been used in several publications before 2000. However, no strict definition could be found for crash compatibility in the literature review of Van der Sluis [114] between 1985 and 2000. He determined some common understandings among the variety of definitions and presented a list of definitions [114, p. 8] from the publications to give an overview of the objectives and aims of compatibility in the research community of that time:

1. EEVC WG 15 summarized its research activities until 1998 in a paper [115]

and defined the term compatibility as follows: “In protecting car occupants most activity has been associated with improving the occupant’s own car to aid his protection. In future, improvements should be possible from improving the front of the other car involved. The term ‘compatibility’ has been coined to describe this subject”.

2. Niederer et al. [116] investigated compatibility measurements for ultra-light vehicles, with a curb mass less than 600 kg, using real crash testing and lumped parameter models. They defined compatibility as follows: “In qualitative terms, vehicles are denoted as collision compatible if their deformation characteristics are such that they do not impose excessive loads on the occupants of the collision partner under a well-defined set of crash conditions. In particular, a collapse of the passenger compartment of the impacted car has to be avoided”.

3. Shearlaw and Thomas [117] reviewed real world accidents to investigate the relation between structural interaction and injury outcomes. They defined incompatibility as inequality in the distribution of deformations and structural characteristics between the vehicles.

4. Audi, Volkswagen, and Seat [118] investigated the potential of computer simulations as an aid to develop crash compatible vehicles and validated their results with full-scale car-to-car crash tests. They did not define crash compatibility, but explained its objective as follows: “The goal of compatibility is [...] to enhance partner-protection without decreasing occupant protection or to optimize occupant protection in such a manner that the overall safety of the vehicle is maximized”.

5. Klanner et al. [119] proposed a rating procedure to assess the aggressiveness and compatibility of cars. They defined compatibility as follows: “Compatibility of a vehicle is defined by both self-protection and partner-protection performance. A compatible car must feature good self-protection and low aggressiveness”.

Van der Sluis [114, p. 3] summarized the definitions and descriptions as one purpose for crash compatibility: “The capability of cars to protect their occupants in crashes, while at the same time produce as less harm as possible to occupants of opponent cars.”

3.1.1.2 European Research Projects

EEVC WG15 did not provide a definition for crash compatibility, which resulted in some disagreements when the working group investigated the PDB approach. EEVC WG15 illustrated several important physical processes and properties that influence the crash compatibility of a vehicle. However, the working group could not identify any validated quantitative method that translates these properties into criteria for assessing crash compatibility. Thus, EEVC WG15 [97, p. 33] declared the necessity for a rigorous definition of crash compatibility, which can evaluate the performance limits of vehicles and outline their requirements for assessing crash compatibility.

Similarly, the VC-COMPAT project did not provide any definition for crash compatibility and remained with the common understanding that crash compatibility considers both, self- and partner-protection.

The FIMCAR consortium also did not provide any definition for crash compatibility.

However, the consortium reviewed the previous works and provided a list of issues [98, p. 107] that are relevant to the objectives of crash compatibility:

• “Compatibility consists of self- and partner-protection”.

• “Improved compatibility will decrease injury risks for occupants in single- and multiple-vehicle accidents”.

• “Compatible vehicles will deform in a stable manner, allowing the deformation zones to be exploited even when different vehicle sizes and masses are involved”.

3.1.1.3 Individual Researchers and Other Experts

Kramer [6, p. 149] categorized the aggressiveness parameters of collisions into three groups of mass, stiffness, and geometry. He defined the compatibility as a term that includes strategies, design policies, and measures to make vehicles compatible against the aggressive properties of different vehicles. Kramer assumed the velocity change as a measure for the collision severity and associated it with the vehicle mass to describe the potential of crash compatibility for different vehicles (Fig. 3.1).

Figure 3.1: Potential of passive safety and compatibility for different vehicles according to the Kramer’s model

[6, p. 156]

Kramer used this model to explain the compatibility measures and their priorities [6, p. 156]. However, the model distinguishes the potential of self- and partner-protection from the potential of crash compatibility, which is not clarified by Kramer. Furthermore, the definition of Kramer does not demand any changes in aggressive designs.

Schwarz and Zobel from Volkswagen AG [120, p. 1] described crash compatibility as “a combination of self- and partner-protection in such a way that optimum overall safety is achieved,” which means that the “compatibility tries to minimize the number of fatalities and/or injuries, regardless of the vehicle in which the injuries or fatalities occur.” They added that customers expect further enhancements to occupant protection, and compromising of self-protection for more partner-protection is inadmissible.

In the same manner, O’Brien [95, pp. 122-128] considered the risk of injury to all road users and defined crash compatibility as “the optimization of vehicle design to minimize the number of injuries and fatalities that occur in all collisions in the accident environment.” He explained that the mean risk of injury in a compatible collision is equal to the mean risk of injury measured in crash tests.