Railway timetabling in Sweden has traditionally been associated with long lead times. In order for the railway sector to be able to compete with other transport modes, the infrastructure manager must become better at meeting the demand for railway services whose need for infrastructure capacity is not well-defined 6-18 months in advance. Research at SICS is changing the Swedish timetabling process so that it will accommodate late capacity requests in a significantly better way than before. This paper describes the principle behind the new method, briefly describes the optimization model that has been developed to support the new process, and presents examples that show how optimization tools can support the new process.