Hi,
The issue with using Clipping splines in this instance is that they don't affect the actual spacing and distribution, they can only remove objects that have already been distributed using the full length of the splines.
In the attached file I've resolved this in a different way, using 3ds Max's recently introduced Shape Boolean object to add the gaps directly to the base spline. Unfortunately Shape Boolean flattens the spline, but you can add a surface to the RailClone object and select the stadium model to reintroduce the stepping.
I hope that helps, please let me know if you have any further questions,
Paul