Signal Control at Isolated Intersections (SCII) has been developed to emulate an adaptive controller using AI technology. It is an application of expert systems to the real-time traffic signal control. The first version of the prototype (SCII-1) was developed in 1987. Subsequent research works were conducted to develop the second version (SCII-2). SCII-2 can be applied to three different types of intersection geometries. It determines the appropriate cycle length, phasing pattern and split, and updates these based on the prevailing traffic demand. It is capable of switching the operation from pretimed to actuated mode and vice versa. Tests were performed to validate the prototype using field data as well as computer simulation. The field test verified the appropriateness of switching the signal operation from one mode to the other. The tests with simulations indicated the superiority of SCII-2 over pretimed and actuated controllers.