Dynamic lane assignment to manage commuter traffic – St Nazaire Bridge

Work carried out for:
CG 44

Key dates
Study and deployment from July 2009 to 25/08/2010

The challenge

The St Nazaire Bridge is one of the crossing points of the LOIRE (North-South axis). The following stretch, composed of 3 lanes, is located about 60 km from NANTES.

Until 25/08/10, traffic on the bridge ran on 2 lanes going up and one lane coming down, with a passing zone, from two to one lane, on the central part of the bridge. 

Because of the residential development on the south bank of the Loire, it turned out that the road narrowing at the centre of the bridge (imposed by the single lane going down) created daily traffic jams in the morning in the South-North direction and at the end of the afternoon in the North-South direction. 

- Traffic jam backup of about 10 km
- Network congestion
- Increased pollution in the passing zones of the Loire crossing atea.
- The construction cost of a new crossing point for the Loire or the widening of the St Nazaire Bridge was much too great for the Department or the State.

Following this observation, it was decided to establish a commuter traffic system, automatically controlled from the ROUTE CONTROL CENTER of the CG44 in NANTES.

This system allows:
- Traffic on two lanes from South to North and one lane from North to South in the morning
- raffic on two lanes from North to South and one lane from South to North in the afternoon
- Traffic on one lane in each direction at night, in order to avoid accidents.
- Complete closure of the bridge in the case of special events (demonstrations or accidents)

And involves:
- Removal of the physical lane allocation by road markings

The LACROIX City solution


Design, manufacture and installation of BRA (Automatic Lane Closure)

Installing automatic road closing barriers with advance warning sign on both the North and South sides to direct traffic to the right lane, for the direction using only one lane.
Automatic road closure barriers


Design, manufacture and installation of gantries

Setting up 104 lane assignment signs above the lanes to indicate whether the lane can be used. These signs are spread over the gantries, every 200 meters approximately; n total, 19 gantries, of which 11 are on new constructions and 2 on beams on the metal part of the bridge.

- Study of the fixing system of the gantries on the bridge piers and the fixing of the beams
- Gantries and beams 100% aluminum, certified FN (French Norm)
- Design and manufacture of lane assignment signs
Supports: masts Lane assignment light signal structures


Design and manufacture of the barrier control elements

Installation of six barriers for the closure of the bridge. Placing 2 VMS (variable message signs) with pictograms and 2 VMS indicating the closure of the bridge and showing the deviation. 
Variable Message Signs


Design and manufacture of the housings

Set up of 29 control housings for embedded red light pads on the road surface. The light pads mark out the white line.
- Management of 14 cabinets by CPL.
- Development of the link CPL

Design and development of the supervision

Installation of an MMI for all equipment enabling management of the commuter traffic system in failsafe mode.

The benefits

Significant reduction of recurrent traffic jams
Installation of roadwork safety equipment and establishment of safety measures for interventions in case of an accident on the bridge.