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Mechanical systems in cars are replaced by electronic equivalents. To be authorized for the road, validation that the replacements are at least as good as the old systems is required. For electronic braking systems (brake-by-wire), this goodness translates to safety in terms of maintaining timing constraints. Yet, in the future, the safety of braking maneuvres will depend, not only, on electronic brakes, but also on cooperative driving maneuvres orchestrated among many cars. Connecting both brake-by-wire on the microscopic level with cooperative braking on the macroscopic level allows for determining safety on a broader scale, as both systems feed from the same resource: Time. This paper discusses work-in-progress, introducing and combining two threads: electronic brakes and cooperative braking. Discussing safety on two levels simultaneously motivates connecting a Simulink model of an electronic brake-by-wire system with the traffic simulator SUMO for conducting the required combined validation. How safe is a car in relation to a given maximal braking distance? What is the optimal distribution of reaction time between electronic brakes and cooperative braking? The validation focuses on non-functional safety limited by temporal constraints (translated to braking distance). It can be exploited in an early validation approach to help reduce costs of more expensive real world experimentation. It can also determine the boundaries at which sufficient safety can be guaranteed.