* Well, I guess you must have modelled / key framed a first car plus associated spline track plus parameters plus spline plus tangent.
* Copying this tag to the new / blank 2nd / 3rd / ... car should allow you to just sweep all frames by some interval.
* As mentioned, I may not understand your problem. Maybe a screen shot or two may help.
I assume that all cars follow the same track (= spline), just with a time gap in between?
So, in my understanding, a single spline with offset start to stop positions must work. The splines are identical (there is only one as all pointers in the tags point the same constructor) but the parameters of the respective tags are different.