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It's been a few years (at least 2 or 3) that we have it free of charge here in Paris too : http://www.sytadin.tm.fr/.

Realtime traffic for major highways, center of Paris, time estimation for the whole périphérique (the ring around Paris), traffic camera at critical locations, all provided by the regional gov. For once, they did a great job.

Nothing new in France either.
Roads have had sensors for at least a decade.
Used for different purposes :
- traffic monitoring (accidents, etc.)
- driver information by huge screens on the road, telling how long to this and this direction ; and I find it really nerve calming to know how long it will take and be able to organize (once it only said how long - in distance - the congestion is, which I don't care about)
- website for 4 years.

Here we have two type of sensors :
- simple loops, which only give information about the "coverage rate" (that is, proportion of time there is a vehicle on the loop. Funnily, this figure is heavily correlated with the state of traffic and the speed of the vehicles. 0.1 is heavy traffic and 0.2 is congestion. I do not recall exacly the figures but you get the highest throughput for a magic "coverage rate" which corresponds to around 57 kmph (~37 mph).
- double loops are simple loops 1 meter away ; correlating data from the two gives you the time decay between them and so the speed of vehicles, in a more reliable fashion than just simple loops ; in particular with these you can ajust the nominal traffic model with observed speeds so your model integrates real road conditions (snow, rain, saturday night...) and single loops can then give you very accurate information.
On heavily trafficked roads (eg Boulevard Peripherique in Paris) you have a single loop every 400m and a double every 2km AFAIR.

http://www.sytadin.tm.fr/tempsreel/parisint.gif
http://www.sytadin.tm.fr/

Great time saver, especially with itineraries now being calculated according to the current traffic data.

http://www.sytadin.tm.fr/tempsreel/parisint.gif
http://www.sytadin.tm.fr/

Great time saver, especially with itineraries now being calculated according to the current traffic data.

which is pretty-darn-close to realtime. a friend of mine
uses this almost as a live tool to tell him when to leave
work for his cross-paris trip home. paris traffic being
what it is, he still ends up parking a lot on the
peripherique, but this helps a bit. :)

ile-de-france traffic site

By the way, again the Paris link, I'm rusty on extrans rules and too lame to hit Preview: Sytadin (Paris/IDF system)

The same thing in Paris. I know one of the computer people working on the paris traffic system. The french have thousands of sensors planted all over the place, as well as hundreds of surveillance cameras.

There have been a number of projects to examine knowledge based "AI style" traffic management. Many small companies offer controller systems which claim to have "fuzzy logic" and are able to learn about traffic patterns. Every single one of them fails when presented with a few basic external factors such as "weekend", "snow", "construction" or "accident". But given a perfect grid system (which Paris is NOT!), and perfect drivers, and the AI systems had no problem finding a perfect solution. But the slightest change threw the whole system into chaos, and quite often killed the system. None of the marketing claims survived even a small real world test.

So Paris has gone to its own system. The computers are doing what they do best, calculating. The humans do what they do best, adding intelligence to the chaos. Together, Paris traffic is only a mess, rather than a permanent gridlock :-)

the AC