A brake control law for vehicle collision warning/collision avoidance (CW/CA) systems has been proposed in the paper. The control law has been designed for optimized safety and comfort. A solenoid-valve-controlled hydraulic brake actuator system for the CW/CA systems has been investigated. A nonlinear computer model and a linear model of the hydraulic brake actuator system have been developed. Both models were found to represent the actual system with good accuracy. Uncertainties in the brake actuator model have been considered in the design of the control law for the robustness of the controller. The effects of brake control on CW/CA vehicle response has been investigated via simulations. The simulations were performed using a complete nonlinear vehicle model. The results indicate that the proposed brake control law can provide the CW/CA vehicles with an optimized compromise between safety and comfort.