This work studies a lane reservation problem with optimally grouping tasks, which aims to design the routes for some special time-guaranteed transportation tasks by optimal lane reservation. Besides, the assignment of tasks to vehicles is optimal decided so as to reduce the number of vehicles and save transportation cost. On the other hand, negative impact on normal traffic such as increase of link travel time on adjacent general-purpose lanes may be caused by the reserved lanes because of the exclusive use of them by the special tasks. Then, the objective of the addressed problem is to minimize the total impact caused by the lane reservation. The lane reservation problem with optimally grouping tasks is an extension of the related problems studied in the literature. A mathematical programming model is then formulated and solved via a proposed approach strategy. Experiment results demonstrates the effectiveness of the formulated model and efficiency of the resolution approach.