The A51 autoroute is a partly completed motorway in southeast France. It is the long-term project to connect Marseille to Grenoble via Aix-en-Provence, the Durance Valley and the Hautes-Alpes department.
The motorway passes the cities of Aix-en-Provence, Pertuis, Manosque, Sisteron and then Digne-les-Bains and Tallard. In the Isère department, it passes Monestier-de-Clermont, Vif and Varces-Allières-et-Risset. The motorway provides access to the southwestern Alps for the residents of the South of France.
Its main section connects Marseille to Aix-en-Provence and the Durance Valley to the north of Sisteron (Saulce). Only 18 km is toll free between Marseilles and Aix-en-Provence, the remaining 128 km is a toll road operated by Escota between Aix-en-Provence and Saulce. At Aix-en-Provence, the autoroute becomes briefly the N296 dual-carriageway between the exits Jas-de-Boufan and Aix-les-Platanes. This section where it meets the N7 was originally proposed to be an autoroute but building has subsequently compromised the route. There is a speed limit of 50 km/h on part of the N296.
A section at the Grenoble end, Varces to Coynelle (17 km), was opened in July 1999. This was extended in March 2007 when the next section, connecting Coynelle to the Col du Fau (10.5 km), was opened in March 2007. This includes 4.5 km which is a single carriageway through the Tunnel of Sinard and over the Viaduct de Monestier. This northern section is also a toll road but it is operated by AREA. This has greatly reduced the summer congestion through the commune of Monestier.
The autoroute recommences 85 km to the north west.
The first section was built in 1953, it connected the Autoroute de nord (open in 1951) to Cabriès. It was only extended to Aix-en-Provence and the A8 in 1970. The construction of the section from Grenoble to Sisteron was subject to protests because of its environmental impact. In 1995 for example, demonstrators blocked work by chaining themselves to construction equipment.
Following many ministerial and policy changes, and tensions between local residents. As a result, the completion of the motorway has been on the agenda for 20 years.
Were all the sections are completed the road journey from Grenoble-Marseille would be 2h40 (instead of the current 3h30). However, there are several problems:
The motorway must pass through the middle of the South-Dauphiné (Trièves) Alps. There were two options for the route between the Col de Fau (Monestier-de-Clermont) and the end of the southern section near Gap:
Following a public inquiry organized between 2005 and 2006, the Minister Mr Perben announced in 2006 that A51 would be built on the Gap East route. However the 2011 edition of the National Scheme of Transport Infrastructure (SNIT) did not include the completion of this section. Completion before 2025 is unlikely.