It branches off from A13 (also known as the Motorway of Normandy) at an exchange known as the Triangle de Rocquencourt located in the town of Bailly and merges with RN12 and RN10 at Bois-d'Arcy.

This project, started back up in 2004 by the transport minister Gilles de Robien, caused significant concern among locals, such as the inhabitants of South of Yvelines.

They object as they feel that this new section of highway will introduce transit of heavy lorries between the A10/A11 motorways and the western A86 tunnel (Rocquencourt), with traffic predictions as high as 100,000 vehicles per day.

In October 2006, following public consultation from March to June 2006, the Minister announced the choice of a 15 km long extension by median route 2C', comprising five interchanges and several covered trenches.

This route provides for an extension that begins in a tunnel at the end of the current motorway, at the junction with the national road 10, then runs along, partially covered, Montigny and the Trappes business area and crosses, partly in a covered trench, the communes of La Verrière and Le Mesnil-Saint-Denis, and ends by bypassing Les Essarts-le-Roi from the west to join the RN 10 at the interchange with the RD 191.