travertine paver installation on a highly expansive soil
A: Yes, laying on top of crushed limestone and sand is the way to go. There is absolutely no need for a concrete base.
Travertine pavers have higher compressive strength than brick and cement pavers, almost double the strength. You should have no issues. On another note, we suggest 6x12 pavers for driveways in the same thickness (1.25 inch)
More information about travertine paver installation can be found here: http://www.travertinemart.com/travertine-installation