One method is to create a horizontal alignment for the shape of the ramp and use it as a horizontal point control for the back of kerb. The template can be setup to contain constraints for the top face of kerb to lower as the back of kerb moves with the point control.
There are some short videos on constraints here that may help if this is a new topic for you communities.bentley.com/.../roadway-designer.aspx
Regards
Paul