About how to improve / fix errors on the tutorial “Quick and Easy Traffic Simulations in Blender! CGC Weekly #19”

Hello.  I’m trying to create a traffic simulation using the blender particle systems with different car models. This is the tutorial that I have used as base :

https://www.youtube.com/watch?v=wWEwxtu9gGc&t=1s&fbclid=IwAR0TmMM3HDO3S-scNSGg4YO4cZsXTCHtFLcydgbTEPvBXrnFEix0S5OGQKQ

BTW my enviroment consists of a two-lane road. I wanted the cars crossed both lanes in opposite directions,so I created two planes called emitter_close and emitter_far with two different particle systems attached. 

These are the values that I have used for both planes :

1. Emissions Number = 300
2. Start / end = 1 – 320
3. Lifetime = 50
4. Random = 0
5. Emit From = Faces
6. Rotation = yes
7. Dynamic = yes
8. Render / Emitter = yes
9. Render / Group = Group_car_yellow / Group_car_green
10. Whole Group = yes
11. Size = 1.860
12. On the Physics tab is enabled the Force Field type = Curve Guide with minimum distance = 1.000

I have also created two mesh groups. Inside each group there are the main components of a car,like :

1. Empty_car_ yellow or green 
2. 4 wheels,parented to the empty_car_yellow,with a driver configured on the X rotation and X location,with :

• Expr = -var ;
• object = empty_car_yellow ;
• type = X location ;
• space = world

             3. another 4 wheels,parented to the empty_car_green,with a driver configured on the X rotation,with :

• Expr = -var ;
• object = empty_car_green ;
• type = y location ;
• space = world

             4. the car’s body meshes 

Each car follow a path,that’s represented by the NurbsPath_road_sx and the NurbsPath_road_dx,with the following parameters set :

• Path animation = yes
• Follow = yes
• Frames = 320

Below you can see how is working the simulation : Is there a way to position cars better than now ? because when they are emitted,some of them cross the ground and some others walk too far above it… thanks.