The Mathilde Bridge in Rouen - a Study About the Impact on Mobility of a Main Road’s Closure in the Center of an Urban Area
SAVARY Michaël, Cerema, MARCHESSE Christelle, Cerema, SAVALLE David, Cerema
This study was launched in 2012, just after a main road bridge was closed in the center of Rouen Metropolis. It aims to reveal changes in mobility during the closure, with a focus on several transport modes.
The river Seine flows through Rouen city in Normandy, in the center of an urban area where 500,000 people live. Mathilde bridge, with highway characteristics, is the most used to cross the river.
Following an accident involving an oil truck which burned, the bridge was immediately closed for a period of nearly two years from October 2012 to August 2014.
Mobility within the metropolis was severely disrupted in several ways. Firstly, people using the bridge had to cross elsewhere, sometimes having to change their means of transport.
Secondly, those who previously did not use Mathilde bridge found that traveling was disrupted by increased congestion on the routes they used to take.
Since the disruption was effective, it was immediately announced that it would last for a long time, so users had to adapt to the situation. The study, conducted by Normandie-Centre Cerema, aimed to understand how mobility practices changed in the urban area as a result of the closure.
The approach involved limits the analysis to crossing the Seine, but takes into account all modes of transport.
The study initially focused on available data from traffic counts data for bridges and ridership on public transport crossing the Seine.
As shifts to these two modes of transport only do not make it possible to explain all shifts from Mathilde bridge, Cerema began a campaign of surveys and counts of pedestrians and cyclists on the bridges.
This innovative approach consisted in asking pedestrians and cyclists about their movements and practices prior to the event. That made it possible to reconstruct the volume of new users of these means of transport without regular counts. It was also an opportunity to test an interview method for cyclists which required the investigators to ride a bicycle too.
These surveys were conducted once during the closure period and once again on year after the reopening.
The following information were learned from this study during closure time:
- the closure of the bridge lead to a significant increase in road traffic on the other bridges;
- a general drop in the number of motor vehicles crossing the Seine;
- a significant increase in public transports attendance, in particular for lines crossing the Seine;
- a significant increase of the number of pedestrians and cyclists using the bridges (the surveys confirmed the link with the truck accident)
The second part of the study about changes in mobility after reopening Mathilde bridge gives the following results:
- a progressive increase in traffic on Mathilde bridge;
- a rapid drop in traffic on the other bridges (a return to previous situations);
- a stagnation of the attendance in public transports
- a slight decline of mobility by active modes on Seine crossings.
In addition, although it could not measure it precisely, the study highlighted other indirect consequences of this type of break in the transport network: a decline in general mobility, trips optimization (especially for non essential shifting), people deciding on which side of the river they are going to live (if possible), increase in carpooling, etc.
This situation is exceptional and contributes to identify in a real case the impact of important disruption in a major network. Conclusions can contribute to risks reflexions (natural or technological) or to the description of mobility behaviors.
Finally, a simulation of this situation with the multimodal travel model available at Cerema enabled to highlight the known limits of trip generation models in the case of a major disruption of the transport offer.
Association for European Transport