The TERGV (for "Regional Express Train on high-speed line") is a model to run trains in Nord-Pas-de-Calais. The idea is to run regional trains on lines constructed for "express trains", instead of the "classic lines". This works only in the case that the high-speed line is used only rarely. Running regional trains on such lines slows down the express trains, and costs more than running them on the classic lines. Despite these problems, the concept is very promising for distances between 100 and 200 km. 