I believe the fast way to animate this , especially in poser 7 would be for each car to be a seperate figure , then

• animate the first car paying close attention to starting position ,
• copy the keyframes from it to each of the other cars offsetting them the right number of frames  (might need a little experimenting .) the animation layers can help keep it neat

it wont take as long to animate as it would to set up complex erc code .

nice train set !

ockhams follower script might work for this .  I think it was in vanishingpoint freestuff . or ockhams bungalow .