This paper presents a multilane continuum traffic flow model for traffic operations at on- and off-ramps, which is based on microscopic principles. One of the main contributions of the derived model is that it takes into account explicitly the impact of ramp length on traffic flow operations, as well as the willingness of drivers to accept smaller gaps when approaching at the end of on-ramps. Different congested states were investigated with the proposed model for specific values of both the upstream main carriageway flow and the on-ramp flow. Several types of congestion states consistent with well-known traffic-congested styles in the literature, such as a moving localized cluster, two moving localized clusters, triggered stop-and-go waves, and homogeneous congested traffic, were found. The simulation results show the stability states of traffic flow for different ramp lengths.