Driving in heavy traffic on a steep road is not quite convenient since frequent use of hand-brake is required. This paper presents the design of brake locking system to replace the use of hand-brake for this particular purpose. The system consists of a hydraulic valve, sensors and a logic circuit which can be fitted in a conventional brake system. Sensors are placed to monitor the engine speed, brake, clutch and gear positions as inputs to the logic circuit. The logic circuit, then, drives the hydraulic valve automatically according to an interlock diagram.