Créteil became a prefecture after the creation of the department of Val-de-Marne, resulting in an increase in population, and a new extension was quickly begun in several stages. The line reached Maisons-Alfort – Les Juilliottes on 27 April 1972 in a tunnel. It enters Créteil on 2-km, open-air tracks in the median of a highway. The Créteil – L'Échat station, with a central platform, opened on 24 September 1973; Créteil – Préfecture, with three tracks and two platforms, opened on 10 September 1974. This was the first Paris Métro connection with the prefecture of a bordering department, extending the line to over and 37 stations.