Merging locations are major sources of freeway bottlenecks. Microscopic simulation tools are receiving increased popularity in analyzing these bottlenecks and designing optimum geometric configurations and control strategies. In congested situations, acceptable gaps for merging are often not available and freeway mainline drivers often cooperate with the on-ramp drivers and create gaps for the merge. This is usually done either by decelerating or by changing to an inner freeway lane. Existing approaches do not capture these phenomena and as a result often over-predict congestion. MIT will develop a new system of driving behavior models, with specific focus on freeway merging behavior. The developed model will be an integrated driving behavior model for lane-changing and acceleration decisions of freeway mainline drivers approaching a merging on-ramp that explicitly captures courtesy and cooperative actions of the driver. Parameters of the model will be estimated with vehicle trajectory data collected by NGSIM at Interstate-80, California during congested periods. The models will be implemented in microscopic traffic simulator MITSIMLab to improve its performance in congested merge locations. The enhanced MITSIMLab will be open-sourced and can serve as an excellent tool for transport professionals to test different congestion management mechanisms.