Douai is a city in France.
North towards Lille, Lens or Hénin-Beaumont
The best place to go is near the "Pont d'Esquerchin", close to the park "Pierre Brossolette".
To go there, you can take the tram line A or bus 8, 15 or 17 to get to the stop "Ecole des mines". There, you follow the road that go North-West for just 100m and you will see a trafic light that bring to a rapid road. You should hitchhike here. There is places to stop, people are driving slowly and lots of people goes directly to the highway A21.
If you are going to Lille or Lens, take a sign and wait for a car that goes directly there. I hitchhike there at least fifty times, and I have never waited more than 15 minutes. The perfect spot for you !
The spot is close to the hospital St Amé. To go there, you can walk, or you can take the bus line 15 to go to the stop "St Amé". When you get there, you will see a roundabout about 50m from you. Go there and you can directly hitchhike on it, just before the exit that shows "A1" or "Arras". There is place to stop and lots of people take the D950. Don't take a car if it doesn't go at least to Fresnes-lès-Montauban. You will easily find someone to Arras there.
If you wanna go to Paris, this place have also a junction with the highway A1 to Paris. There is 2 roundabout there. Ask your driver to let you at the roundabout that goes to Paris, and hithhike on it. There is place to stop and it's very easy to find a car that goes to Paris.