Honey has become reactive to cars and lunges and barks as well, although she's acting from a fear base more than a herding instinct and is trying to get away from them usually.
When I see one approach I step to the side with her, we go about three feet into the grass so we're well away from the road and the car, and I have her sit.
I take out a treat so she knows I have one and can focus on it. I make her sit until the car has passed and any tension is out of her body and than she gets the treat. All the while I keep her focusing on me and the treat and I talk calmly to her telling her she's a good girl.
The treat is usually turkey, because that's her biggest motivator, although yesterday I tried mozzerella cheese and she responded very well to that. In the beginning we had to have treats everytime time with every car, now I bring them every couple of weeks just as a reinforcer.
I don't know how much success you'll have with this if Laddie, (I believe?) doesn't know the sit, stay or a listen command at his name. Honey is also trained not to take food from my hand unless I give her either a verbal or physical sign that she's allowed (a flat hand means it's okay to eat, a slightly cupped hand means don't touch it even if I'm shoving it under her nose. (I am prouder of this trick than any other she knows!)) Honey didn't start her actions until she was almost two, and before that she was already trained to move to the side and sit whenever a car went past. (Although sometimes I wonder if that didn't start her paying a little to much attention to cars)
You'll see small amounts of progress at first, it's a very hard instict for them to control, keep calm while you work with them. If they aren't getting it, try finding a park that has a path farther away from the road, where you can still see and hear the cars but they aren't as close. Possibly try to find an area with a low speed limit as well, maybe a school zone? For honey the faster the car the more she reacts. Sometimes if I know she's going to react extremely strongly, (a very fast moving vehicle, or a large white one are both strong triggers for her) I will kneal down beside her and put my arm around her as an additional support. The restraining hand reminds her what I want and that I'm there. If I know there's no hope she'll manage by herself, either because she's just having a really bad day or she's overly excited from seeing critters or playing with her freinds I'll pick her up and hold her instead of making her try.
It's also possible that a completely different area will kind of bypass this section in their brain. If I bring Honey to a nearby historical district, which has a nice square and lots of little shops and is very busy with people as well as cars she has no reaction at all to the vehicles, even if we're walking across or right beside the road.
Good luck on your work with him, don't give up even if it seems impossible at first, Honey has been dealing with this since this winter. She still has bad days, but more and more of them are becoming good ones, it just takes lots of time and lots of work and loooootttts of patience.
However I would hate a sail Fillion even more!!