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| French leave - holiday season prompts new traffic management system in Avignon.
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20/8/04 |
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French traffic managers are hoping a major trial on one of the country's busiest holiday routes will pave the way towards significant improvement in traffic flows together with reduced congestion and fewer collisions.
Using specially written algorithms and a range of ITS technologies, the state-owned motorway construction and road operations company , ASF (Autoroutes du Sud de la France) based in Avignon, is spending the month of August testing a new management system on the A7. The north/south route linking northern France with Spain and Portugal as well as the Cote d'Azur, sees traffic flows increase from a daily average of 75,000 to around 110,000 during the holiday period resulting in serious congestion and an increase in the number of accidents.
"Relatively minor incidents" will often result in queues of up to 15 Km with the impact felt on all the surrounding routes," explained Nicolas Schwab, a Traffic Manager with ASF. "Diversions involve sending drivers considerable distances onto the already crowded A75 and A51. On top of this we expect the position to worsen with traffic volumes on the A7 forecast to grow by 3% a year between now and 2010."
In an attempt to deal with the problem, ASF began developing a proprietary algorithm designed to give advance warnings of congestion, based on historical traffic flow data from inductive loops buried in the carriageway. In essence, the algorithm allows traffic engineers to predict traffic jams up to 45 minutes before they become a problem.
"We began testing the system, off-line, in 2002 and 2003 to ensure that it would work under operational conditions," said Schwab. "This year, on 31st July - the day the French begin returning from holiday and known locally as Black Saturday - we set up a system of traffic management on the 90Km north-bound stretch of the A7 between the cities of Orange and Valence. Data, including vehicle classification, traffic volumes, speed of traffic and lane occupancy rates are all obtained from Traffic Counting Stations (TCS) linked to inductive loops in the roadway (1 TCS every 5 km on this stretch). The data is fed directly to a processor in the main control room in Avignon and two regional centres at Valence and Orange."
Any anticipated interruption to the flow of traffic results in an alarm signal to the control centre where the situation is checked by an operator using a PTZ (pan/tilt, zoom) CCTV camera. If necessary, the operator will alter the mandatory speed limit pictograms (70, 90 or 110 kph) mounted on overhead gantries and display the "Vitesse Limitee" (limited speed) text on an adjoining VMS. At the same time an ASF mobile patrol is dispatched to deal with the incident.
"Although the speed limits shown in the pictograms are mandatory," said Schwab, "we have, as road operators, no authority to enforce them. Instead, we used ANPR software linked to fixed cameras and take the average speed of the vehicle over a set distance. If this shows that it was speeding, a VMS illuminates showing the vehicle's number and warning the driver to slow down. Early indications show that three in every four drivers are keeping within the speed limits. Roadside surveys also suggest the scheme is highly popular with motorists who face fewer hold-ups on their journey home."
The trial, which ends on 6th September, will be evaluated with a view to extending it to other parts of the primary route network, including the southbound carriageway of the A7. Anticipated enhancements include fully automating the process of altering the permitted speed limit and posting messages to VMS from a menu of pre-prepared texts.
Results of the evaluation process are expected to be made public before Christmas.
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