In my first couple of years in France, I did not understand that it was not a good idea to travel on August 1st or 15th. As a result my family and I insouciantly left for Paris from Normandy at about six o'clock one evening. It's a two-hour drive. In the small hours of the morning, exhausted, we found ourselves on a route nationale (a smaller highway which we had taken to escape a horrendous traffic jam on the autoroute), 70 miles from Paris, absolutely stationary. People were having picnics on the roofs of their cars.
To avoid this scenario, I quickly learned to take advantage of the Bison Futé ("canny buffalo" or "clever bison"), a French-government-run program to help people avoid traffic jams. Today, for example, its webpage looks like this:
It also has an English version-- annoyingly signaled by the British flag, even though very few of the world's English speakers are British and we actually fought a couple of wars not to be-- which offers a "Live Informations Map" (no need to find a native speaker, apparently).
The former logo of Bison Futé, a green buffalo, has recently been replaced with this one: