As a kind of typical bottleneck influencing the transportation seriously, the lane reduction has seldomly been investigated with the optimal velocity model. In this paper, we study this issue using the optimal velocity model, in which two kinds of vehicles (fast and slow) are introduced. The asymmetric lane changing rules in the slowdown section and the lane squeezing behaviors at the bottleneck are taken into account. Under the periodic boundary condition, the numerical simulations are performed. The fundamental diagram is obtained. Then, the influences of speed limit and the length of the slowdown section on traffic are discussed in detail from the view of traffic control. The currents are dependent on the speed limit, but independent of the length.