When I take chickens to shows and it's going to be a long trip, I usually keep chicken groups together who already live together. If you have a roo who is amorous, the hens will appreciate him riding separately.
We drive a hatchback. We drop the back seats and spread a tarp with the edges up a foot or so on all sides, to protect the car. On top of the tarp we place a large dog crate or carrier with a thick layer of straw on the bottom. The straw gives the chickens a much better ride, absorbing some of the bounces, and keeps them from being tossed around in traffic or curvy roads. But, sadly, nothing will absorb the smell of chicken poop. And chickens create a lot of dust and dander.
On the way, you will want to feed them and give them water. Feed can stay in the crate, but it's best to give them drinks just at your rest stops.
Be aware that they will sleep when it's dark, but if a truck with bright lights comes up behind you, or when you pull into a brightly-lit rest area or through a brightly-lit toll area, they will wake, and the roosters will crow.
If you are traveling while it's hot, you will need to take all the same precautions for overheating that you would with a dog or any other pet.
When you get to your destination, you will want to remove the crate and carefully remove the tarp and shake it out, then wash the inside of your car. Seriously, you will want to!
Hope this helps. We travel with chickens and ducks all the time, and it's not a big deal. It's actually quite a bit of fun to see their reactions to life on the road, and other people's reactions to them.