Nowadays, the capacity of the lock becomes more important, since ports become busier and waterways more crowded. Still, the management of locks has not changed very much. Especially since locks are one of the most important factors that determine the capacity of a waterway. A lock limits the capacity of a waterway in two ways. First of all, the lock restricts the dimensions that can pass through the locks. Secondly, the lock limits the flow of vessels that can pass through the waterway. Since the dimensions of a lock are not likely to change, the focus of this study will be on the flow of the vessels. The question that will be answered during this study is the following: Which lock operation policies should be applied under which circumstances in order to contribute to an increase of the efficiency of the locks? A lock operation policy is a way in which the lock can be managed. This concerns both the order of vessels as well as placing vessels in a chamber. The circumstances can be divided in two types; the factors that determine whether a new policy would contribute to better performances and the general characteristics of a lock which need to be present in order to apply such a policy. The following policies are taken into account: 1. First come, first served (FCFS). This category is commonly used in practice and focus merely on the arrival time of the vessels and does not take into account the use of resources for determining the order of vessels 2. Shortest Processing time First (SPT). By using this policy, the vessel which has the shortest processing time is chosen to pass through the locks first. 3. Resource-based selection (RBS). This policy ensures an efficient use of the resources, since vessels who need resources are planned before the vessels who do not need resources. These three alternatives are compared with each other by means of a case study at the port of Amsterdam. The FCFS policy is used as the initial situation, while the other two policies are compared with this policy. By just comparing these policies based on the current arrivals at the port of Amsterdam, the results are almost equal. The reason that the capacity of the lock is not a problem yet and therefor other policies will not be more effective than the current one. By increasing the number of arrivals some interesting insights could be gained. First of all, both alternatives gave better results than the FCFS policy. The SPT reduced the waiting time for the locks and decreased the number of lockages. As a result more vessels could be handled. The RBS policy reduced the waiting time for resources and therefore increased the number of vessels that could be handled slightly. It can be said that the choice between those policies is dependent on the factor that limits the capacity. The table below shows a small part of the results of the study. It can be concluded that the FCFS policy is most efficient considering the number of lockages. The total waiting time is more or less equal. If the number of arrivals increases, the waiting time of the FCFS policy starts increasing faster than the other policies. The number of lockages remain lower than the other policies. This trend remains if the number of arriving vessels keeps increasing. The next step that has been taken is the generalization of these results. This concerns the circumstances that determine the success of specific lock operation policies and lock operation policies in general. It should be noted that the factors which are present in a lock system, but do not influence the effectiveness of a lock operation are equally important, since these factors can be neglected during the choice of the lock operation policy. These factors are the size of the chambers as long as there are multiple chambers, the pattern of arrivals and to a certain extent, the fleet mix. The factors that influence the effectiveness of the tested lock operation policies mainly concern the physical characteristics of the locks. If there are obstacles such as other locks near the lock, the effects of the tested lock operation policies are almost diminished. A second factor is planning horizon. If the arrival time of the vessels is known just before the arrival itself, it is nearly impossible to optimize the order of vessels. A last factor is the place of the lock in comparison with the sea and port. If the lock is located far from sea, the influence of the tide is larger. This results in less possibilities for changing the order of vessels, since the timeframe for most vessels is smaller. The effectiveness of the lock operation policies might also be influenced by some external factors. The first one are the weather conditions. If the weather conditions are bad, the choices might be limited. It might for example not be possible to handle large vessels or use a certain chamber. A second factor is the hydrological conditions, such as tide and current. Those factors can limit the flow of vessels regardless of the policy. So it can be concluded that it is possible to apply the results of this study in more situations than just the port of Amsterdam as long as the factors above are either met or taken into account. Since it is clear that the results of this study can to a certain extent be applied in various locks, the main research question can be answered. Which lock operation policies should be applied under which circumstances in order to contribute to an increase of the efficiency of the locks? The first conclusion that can be drawn is that the availability of resources can influence the choice between those policies. If the resources are scarce, it is better to focus on the resources and select the RBS alternative. However, if the focus is of the managers is on the environment and reducing costs, it might be considered to use FCFS, since this limits the number of lockages, without complicated rules or algorithms for planning which can increase the costs of the policy. The second conclusion that can be drawn is that the RBS principle is only beneficial if the number of arrivals is high and the resources are scarce. Even then, the average waiting time is not likely to decrease. This is due to the fact that the benefits of the RBS policy are diminished by the increase in waiting time for the lock itself. The number of vessels that can be handled will increase nevertheless. The third conclusion that can be drawn is that the same conclusion can be drawn about the SPT policy. If the number of vessels that arrives at the lock is limited, the possibilities to change this order are limited as well. Therefore, the SPT policy will only be effective if the number of arrivals is larger. The choice between the RBS and SPT is mainly dependent.