Sheri
The vast majority of roads in New Zealand are constructed of a granular type material similar to what you're constucting.
The main reason that you put filter fabric down is due to a concern that fines (mud and silts) will slowly move up from the insitu (existing) materials and into you...
We use the MX suite for all our civil design works. Roads, site, rail, drainage etc. this suite works in windows standalone and inside ACAD and Microstation so we are producing final drawings direct from the software. I have been using it for over 6 years and find it fantastic for the one off...