This presentation focuses on capacity drop at freeway merges that occurs when vehicles from the on-ramp insert at low speed. Such an inserting process leads in some circumstances to an active bottleneck with congestion upstream. The inserting process is first described on an individual basis using the moving bottleneck theory. Using the variation theory, we are able to integrate the local processes and derive the mean capacity value. We will show that the inserting position on the on-ramp plays a crucial role in the global process because it generates complex interactions between inserting and mainstream vehicles. Heterogeneous vehicle characteristics can be taken into account by carefully investigating the statistical distributions associated to the flow dynamics just upstream of the merge. Finally, we will show that the proposed analytical framework can easily be extended to account for multi-lane traffic on the freeway. Such a framework provides at the end implicit analytical equations that can be solved with any classical numerical solver to calculate the effective capacity on each lane when merges are active (head of the congestion).