It is well known that under the condition of high traffic volume lane-flow distribution becomes unbalanced; more traffic tends to use a median lane rather than a middle and outer lane, which causes the deterioration of traffic capacity at bottleneck sections. By employing the technology of ITS, balancing lane-flow distribution is one of the feasible solutions to increase the throughput of bottleneck flow. However, the mechanism of the unbalanced usage among lanes is still unclear and traffic flow models enabling online and network-wide evaluation of dynamic and strategic lane management have not been proposed due to the lack of the method to computing lane-based traffic flow including lane-changing dynamics. This paper developed the multi-lane first order traffic flow model, which depicts the dynamics of lane-changing. Assuming that each vehicle changes the lane to improve its utility or decrease its disutility, and the equilibrium of lane flow distribution is achieved as the condition of stochastic user equilibrium (SUE), it is revealed that the proposed model can represent the equilibrium curve of lane-flow distribution, and depict the propagation of traffic congestion at a lane-drop bottleneck section.