This project examines the capacity of signalised intersections. The purpose is to determine the effect of various signal control forms and geometric changes on the capacity of the intersection. The project has been carried out in the micro simulation program PTV Vissim 11. A fictive intersection has been built in Vissim in accordance with Danish norms and practices. Five scenarios have been created, with each scenario featuring a change of one parameter. Each scenario is tested with a large number of different traffic volumes. In Scenario 1, there are only two phases with no turn phases. The model has one through lane, one left turn lane and one right turn lane in each of the four directions. In Scenario 2, there are unprotected left turn arrows for both left and right turning traffic. This increased the overall average delay per vehicle, but decreased the maximum delay in the intersection. In Scenario 3, the protected left turns are introduced. These improve the traffic safety, but drastically reduce the capacity of the intersection. In Scenario 4, an extra through lane is introduced to counter the negative effect of the protected left on the capacity. The capacity in Scenario 4 is vastly improved from Scenario 3. In Scenario 5, the economy of building the intersection is taken into consideration. There are only two through lanes in the area of the intersection, while the roads only have one lane outside the intersection. This meant a small drop in capacity from Scenario 4. Lastly, all five scenarios were tasted with an intelligent adaptive signal controller from the company Advanced Traffic Systems. This showed an overall improvement on the capacity. It was mainly in the scenarios with protected left turns and with high traffic volumes that the ATS controller had a vast positive effect.