You said you want it to follow a long straight path, but then you said it needs to go down and back (up and down?) and has many turns, which isn’t a ‘long straight path’.
Do you mean you have a curving, up and down road, but you want your vehicle to stay within the lines on the road?
Type ‘ai cars with nodes’ in the Search bar up top to have scripted movements of the cars.
The other way would be to put single rail tracks made of Parts hidden a few studs under the middle of each lane, then put 4 Parts around each track as a guide (1 per car) and use a CollisionGroup which only collides with itself for the rail parts and the guide parts.
I use this as a track for a boat to follow around between islands in one of my games.