This paper presents an interactive planning system for forest road location. This decision support system is based on an interactive heuristic approach referred to as interactive large neighborhood search, within which the user contributes in a cooperative manner to the optimization process. The objective of this cooperative optimization process is to exploit the problem-domain expertise of the user in order to, on the one hand, guide the search for a solution towards intuitively interesting parts of the solution space, and, on the other hand, generate more practical solutions that integrate aspects of the decision problem that are not captured by the heuristic objective function. This paper more specifically presents the user interface, the interaction mechanisms and the heuristic developed to support the cooperation between the computer and the user. We also present experimental results based on real problem instances, with an expert user. A comparison shows advantages for using the proposed interactive approach over a pure manual or pure automated approach.